What is the purpose of a filament choke in the filament of a triode grounded grid amplifier
The design of the small-signal amplifier may be based on the small-signal AC parameters of the valve, mutual conductance (g m), dynamic anode resistance, r a, and gain μ which are described in Introduction to Thermionic Valves (Vacuum Tubes). Watts Output 1500W . trans- mitters in the 50- to 100-watt range required to drive the grounded-grid brutes have become widely distributed. If all negative feedback is bad, then we should never use triodes, input cascode circuit features a slight twist: the top triode's grid is not grounded, Oxide Cathodes, Thoriated Tungsten Filaments, R-F Power Amplifiers, Use of EIMAC Tube Perfor. 4) exposure is terminated thru a grid controlled (triode) xray tube. “Filament Fuse” for HV – See “The Care and Feeding of Your 30L-1” Necessary (See pg. Inside the tuned input enclosure. The control grid serves the same purpose as the grid in a triode, while a second grid with the same number of bars as the control grid is mounted between the control grid and the anode. 2 below) See “30L-1 Instability – A Don Jackson Analysis” Recommended Other than these important and well-engineered changes, we recommend that you just enjoy your amplifier until it gives you a problem to consider. Grounded grid RF amplifier feeds an autodyne converter to produce the 200Kc/s IF. Tubes with cathodes (indirectly heated) are versatile. The plate supply can be choke or capacitor input. s. A 5 to 5. 1 and No. One thing not discussed thus far is the option of resonating the filament choke on the lowest frequency band, and then add shunting inductance to get higher bands. capable amplifier for use in the ham shack. 01 capacitor from grid to ground is to “tune out” the the weight of the HV xfmrs, filament xfmr, filament choke and other items. 29 inch. Filament Choke - AG6K - "For a HF application, a garden-variety 0. My friend reported that it was also on his grid-choke 300B SET as well as on the D3a-E180F RIAA preamp. The input tuning uses a Oct 1, 2005 Input impedance of grounded-grid triode amplifier Advantages: Inexpensive, tough, directly-heated filament simplifies cathode. Could this grounded grid grounded grid Fig. 1) is a popular topology for many different operating frequencies. Hum from the heater (filament) is the easiest to take care of. Tubes With Cathodes. Trim the circuit board wires to length and solder their connections. D. Looks like a 500K pot with an SPST switch that I can get at AE (Used the same one for a 1947 Magnatone M-197-3-V that I just repaired). The Dummy Tube. - 15 Khz (± 1db max. differs from general-purpose voltage regulators in a number of ways:. Do a thorough final inspection before startup. However, no grid and no screen is perfect--so some of the damped wave VHF signal at the anode is capacitively fed back to the input--and amplified. The two HT (250v + 100v) rectifier valves are type CV493 or 6X4. The 4S Universal preamp is a super simple single stage line level Hi-Fi preamplifier that will work with any of the 9-pin miniature 12A*7 twin triode tubes (12AU7 12AV7 12AY7 12AT7/12AZ7 12AX7). A good example of a valve with a directly heated filament cathode is the 300B triode, manufactured since the 1930s and still in use today (we will discuss the triode in more detail later). The source of electrons from the cathode is through the big 25 watt 880 ohm cathode resistor that goes to ground. e. The 3-500Z is a relatively inexpensive tube and has been around for a long time. chokes must be employed in the filament circuits to prevent oscillations. Pleasures and Pitfalls of Linear Amplifiers 4Tuned Input for the Grounded Grid GS-35B triode. From this, the output tube 833 A is powered through the reverse drive transformer. T he use of the grounded grid amplifier using triode valves (Fig 10. Tuning is by a high voltage 150 pF variable capacitor. It There are five main parts inside a pentode tube, which are the cathode, grid, screen grid, suppressor grid and plate. A unique application is possible with 20B, called the OTA amplifier. The purpose of this paper is to explain the selection process and trade-offs involved in choosing the circlotron as the optimal topology for a high-power OTL amplifier. A reduction in filament voltage will lower the filament temperature, which will substantially increase life The control grid serves the same purpose as the grid in a triode, while a second (screen) grid with the same number of vertical elements (bars) as the control grid is mounted between the control grid and the anode. A trifilar-wound filament choke (6. The directly heated type, are found in most all of the glass enveloped power tubes, using Thoriated-Tungsten as the filament element. ) Expired - Lifetime Application number US182101A Inventor William R Baker So, the grid is often plated with a metal that is less prone to secondary emission, such as gold. 9 again shows the basic amplifier circuit but this time it uses a valve with the input-connection (the grid) connected to ground. Except for heater The Ameritron AL-80A uses a single 3-500Z triode to produce over 1KW of power MOV's from the filament wires to ground near the filament choke bypasses. The 12AU7 tube's filament is driven directly from the 12. If you choose to omit this stub from your amplifier, you MUST add an RF choke from the amplifier antenna output to ground. dia) forming the bridge of the "T," and a 10-75 pF variable capacitor for the arm. , Marion, Ind. cathode filament, control grid and an anode. The parasitic suppressors are made from silver plated wire, 6 turns on a 1/4 inch form and paralleled by a 100 ohm 2 W non-inductive resistor ending with the ceramic plate caps. 3 Volt heaters, the 6A6 and 6N7 are equivalent to the 53. This group of amplifiers was referred to as the EL6400 series. R. 3 V Direct inter electrode Cin capacitance (grounded C grid) oul Cpk Amplification factor (average) Frequency of maximum rating cw DC Plate Voltage (max. (Sometimes the cathode IS the filament — this is called a Directly Heated Triode or DHT) In a typical amplifier like we will be building, the plate (a. the filament and varying the screen, or number 2, grid voltage from zero to nominal positive potential. leakage current at 5kV between Anode and filament. The screen-to-grid amplification factor of most tetrodes, such as the 4-65A, 4-400A, and similar tubes, is approximately 5. 6 filament by-passing 60 3. This can allow the filament to pull to a high voltage of 1000 volts or more. Assuming a floating filament circuit, each of the two supply sides will have some, different, capacitance to ground as well as some, different, capacity to each tube grid. Peck, W6SNO One-Band Kilowatt Amplifiers Using the 4-125, 4-250, and 4-400 in Kilowatt Amplifiers— Raymond F. The schematic for the amplifier is shown in Figure 1. Oxide Cathodes, Thoriated Tungsten Filaments, R-F Power Amplifiers, Use of EIMAC Tube Perfor- Cathode-Driven Amplifiers, Grounded-Grid Ampli-. SV811-3 is a power tube developed by Svetlana, Russia basing on the transmitting tube 811A. These are: A. The SUPPRESSOR GRID (GRID #3) regulates the flow of electrons in the tube in the same way as is the case for Control-grid #1 and Screen-Grid #2. Grid. Fig. Yet there is an alternative. Circuit of the grounded-screen amplifier with the control grid returned to a tap on the bifilar filament choke. they have filament, use solid state rectifiers and have as a side benfit a HV teminal and a low HV terminal, you can run this rig off the low HV terminal and run an added amplifier off the Hv terminal itself. At the rated (nominal) filament voltage the peak emission capability of the tube is many times that needed for commu - nications service. The filament is also the cathode, and the output is equally sensitive to noise voltage on the grid or cathode, so the power source must be especially quiet. Watts Input 90W. The VHF signal is fed into the triode of a 6BL8/ECF80. Miller 8107 choke (digikey # M9842-ND On the 12AX& that is used for the Normal and Brilliant channels. A 3CX800A7 External Anode Triode with forced air cooling and modern stripline circuitry, insure efficient and conservative operation. stages and the 807 audio stage. filament warm-up time of five seconds is normally sufficient before commencing operation at full power. The 3CX3000A7 high-mu forced air cooled power triode provides relatively high power output as an amplifier, oscillator, or modulator at low plate voltages. b. Individual Test data, such as: Matching Data, Grid Current, Vacuum, Filament Current, etc. There are at least 2 different purposes for multiple filament chokes that may impact the selection. , no choke etc). 26 DHT Gen3 ready to be tested. 5", Mu=125 rod, 3" long can be used to . A bifilar wound choke isolates the RF section of the cathode from the filament winding of the power transformer. "Grid Stopper" Resistors The AC-30HW had 3300 ohm control grid or "grid stopper" resistors installed on each of the four EL84 power tubes in the output amplifier stage. The piece has a filament transformer mounted under the chassis. Commission rating the a approve Of carrier Tuned Input for the Grounded Grid GS-35B triode. A Line Stage pre-amplifier needs to offer the facility to select between different sources, to provide some means of attenuating the chosen source and then deliver it in an The plate choke is a simple 3 to 30 MHZ variety with a value of 55uH. Special surface finishing is also used to help prevent secondary emission. The 833-A Stereo Amplifier: When I first began building single ended triode amplifiers the vacuum tubes of choice were the 300-B, the 2A3, and the 45. The Commander Il is a Grounded Grid class Ab2 Linear Power Amplifier that operates on the Amateur 2 meter band. The length of the coax between the driver and the tuned input affects the interaction. Take a look at this scan from the RCA Receiving Tube Manual. bifilar 10 µH filament choke part. Note that on the EL34 CCSs, the screen grid is bypassed by a large capacitor to the cathode of the tube. - All board inlets and outlets by screwed terminal blocks and IDCs with flat ribbon cables. It is essentially a low gain power amplifier with a voltage gain of under 4dB. At the IF frequency, the circuit is resonant and therefore high impedance; that is, the amplification of the stage is reduced. parasitic choke was required with this grounded grid triode and filament chokes in parallel, the RF drive coupling caps and. Testing Firing up an amplifier for the first time can be a scary proposition. As we can see on the diagram above, there are some interesting topologies for consideration: Two regulators with fixed bias (Circuit 1): Each DHT valve has its own fixed bias at the grid (circuit omitted for simplicity) and each filament has its own Rod Coleman regulator. The screens typically take around 5-10mA each, and the preamp tubes draw about 1-2mA or so (for the typical 12AX7; 12AT7's are usually biased for around This power supply is powered by the unfused filament-transformer. In pentode mode with fixed Eg2 and fixed grid bias the Ra measured could be 40k and this does not mean the Ra is equal to a 40k resistor. In summary: The screen grid, control grid, and cathode are used as a grounded screen (plate) crystal oscillator, while the cathode, control grid, and real plate are used as an amplifier. 3V filament winding, use the lower wiring that produces the lower voltage. Jul 31, 2017 · The most popular SET amplifiers use three types of triode tubes: the Thomas Mayer SE 45 Triode Amplifier The 45 is a filament type triode RADIO FREQUENCY LINEAR AMPLIFIER Interelectrode Capacitances' (grounded filament connection) ated as a grounded-grid rf amplifier, the use of. during an 'event'. I haven't decided on a design, and I bought several homebrew amplifiers, and have been looking at the designs and construction for ideas. Each tube has a 5 Volt/20 Amp filament requirement. The center-tap of the filament winding is grounded to a lug of the 6X5-GT socket ring, and the 6. Thorough fluid cooling and individual pantographic suspension of the filament strands provide'a thermally stable structure. The purpose of the choke in these type supplies is not for filtering and voltage regulation, but just for filtering the DC supply to the screen grids of the output tubes and the preamp section. RCA 1933 AN-14 Operating Conditions for the Type 53 - The high-mu twin triode type 53 can get ten watts in zero-bias class B operation. The following illustrations show the structure of a directly heated thoriated filament valve of the 1920s-1930s (similar to a Mullard ORA), compared with a The driver stage uses a high-gain 12AX7/ECC83 dual triode that operates as a grounded cathode amplifier. The most widely used small triode, the 12AX7, is a dual triode which has become the standard small-signal amplifier in guitar amps. Comments? in normal Amateur amplifier service? Should I care about It wasn't just the amount of voltage between grid and filament that Thus, the triode functions as an amplifier of the incoming AC signal (taking To do so leads to unbalanced currents in the filament choke and hum modulation of the RF output. The triode tube has two sections, and one is used for each channel. The Harbach fan mod has been around for a while. The amplifier is based on a single 3-500Z in grounded grid. The high-Mu grid employed in this tube The amplifier is a grounded grid triode tube pair connected in a push-pull manner. The L between the 2 capacitors in a pi-section filter, or the choke of a choke input critical L filter, does this. neutralized triode amplifier, a small portion of the output signal is purposely fed back to the grid circuit. The preamp design is straightforward, using EL34 pentodes wired as CCSs as the plate load for the low-mu triode. Thus, if a filament-to-grid short occurs, and the amplifier is not switched off promptly, the filament-transformer will literally melt-down and short-out. The filament of the amplifier tube is lighted, the positive plate-supply lead disconnected**, and r-f excitation from the driver stage applied. Check the #47 lamps and filament A signal is applied to the grid circuit of the screen grid tube 4 causing current to flow through the block diagram 1, creating the bias function heretofore described, also through the resistor 18 thereby putting a negative bias on grid 17 of the triode 8, blocking its plate current so that there would be no voltage difference across its plate chosen as most appropriate for the purpose. Grounded-grid &AM4 HEATER AND FILAMENT SUPPLIES: Valves are designed to operate. The third meter of 0-10 volts range, meters the filament of the power amplifier, and the fourth meter, a 0-100 ma. The grid chuck assembly of each tube is combined with a resistor 549 surrounded by a choke 550 to further stabilize the grid circuit. Best grid geometry ensures uniformity and linearity of the tube curves. This is necessary to keep the triode from oscillating at IF frequencies. 1 Khz). Specified in hexode unit; P, pentode unit; T, triode unit; TR, tetrode unit. The tube has a low inductance cylindrical filament tank circuit for VHF operation. The filament of this direct heated triode are connected directly to ground via the center tap ( midpoint ) of the heater winding. 5 Volts AC for the filament supply so there is a 100 ohm potentiometer across the filaments. I tried D3a, C3g, 18040 (old Philips predecessor of Germany C3g). 2) a charger button is pressed immediately prior to exposure to charge the capacitor. Variable Vacuum Capacitors from Surplus Sales Try Here! you can also get the diodes, isolating capacitors (1000pf 20kv) the bifilar choke, the electrolytic capacitors, filament transformer, the tube, base and chimney, in fact most of the bits can be obtained The 1 ohm resistors in series with the 12BY7 filament reduce the filament voltage a little so the tube runs cooler, thus reducing hum and noise pickup. As a class B linear amplifier in single-side- band service, a triode-connected 7094 with forced-air cooling can handle a peak-envelope- power input of 350 watts with only 1750 volts on the plate and zero bias on grids No. :?' It was known by the writer that triode amplifiers do not function properly when signals of the very high frequency range are encountered? As a general rule, put circuits for grounded-grid applications and is conveniently terminated in a ring between the plate and filament terminals. In parallel with the tube, there is a rectifier and a buck converter module that step down the 12 volts into a usable 6. The sound of the amplifier is characteristic of triodes: smooth and The Hammond HL1000A HF Linear Amplifier is a one-stage linear amplifier using one glass envelope 3-500Z Eimac Triode. The triode section of V1 serves as a voltage amplifier with a gain of approximately 10-15x and the pentode section is a power amplifier with an audio output of around 4 watts. Less hum in the output is the result. (Cascade. ) SV811-3. Forum • DHT preamp with 1920s UX Oct 03, 2018 · DIY DHT filament strategies. The passive grid configuration has a couple of advantages compared to a grounded grid design. Overall voltage gain is determined by the mu of the triode which is ~8 for both the 01 and the 26, the winding ratio of the plate to line the grounded side of the first filter capacitor connects to the star ground through a wire that is physically separate from the return wires in the rectifier loop; this wire connects to the capacitor terminal, not somewhere along the rectifier return wire. The GS35b is a Russian triode that is relatively cheap and easy to get hold of. GROUNDED GRID TRIODE HF LINEAR AMPLIFIER Installed the 3CX3000F7 filament transformer, two 30 amp filament chokes in parallel, the RF drive coupling The Eimac 3CX1500D7 is a compact power triode with an anode dissipation rating of 1500 watts. If you haven’t built a DHT preamplifier then do it. 12 power supply consideration 75 3. Inside the Anode Compartment . Only the filament voltage needs to be changed. I suppose that it could be triode strapped, but the output power would be fairly low, about 1 wat or slightly less. However, the tuned input circuitry for multi band Class AB1 grid-driven operation is comparatively simple. Is highly negative with respect to the plate and returns secondary emission to the plate, increasing the permissible gain and the tube efficiency B. Grid-wire-to-filament-strand spacing is 0. The first and most important is to provide a dc path to ground should the plate blocking capacitor fail. No voltage regulation or semiconductors are used in the design. Obviously with 88dB efficient speakers you can tolerate a couple of mV of ripple at the output of the amplifier before it starts to become obnoxious. ) Expired - Lifetime Application number US363185A Inventor William O Brooks POWER TRIODE 3CX1500D7 The Eimac 3CX1500D7 is a compact power triode with an anode dissipation rating of 1500 watts. Power outpout is 1100 watts. POWER TRIODE 3CX1500D7 The Eimac 3CX1500D7 is a compact power triode with an anode dissipation rating of 1500 watts. 1. function of grid voltage for a high power thoriated tungsten filament. In a grounded grid amplifier using a triode vacuum tube, the input signal is applied to: brought through a filament choke. A final note: The tube manuals instruct you to tie screen grid, suppressor grid, and plate together to make the triode connection for a 6AU6, with a maximum plate supply voltage of 250 VDC. The pre-amplifier topology is a zero feedback common cathode direct heated triode stage transformer coupled to the load. , Renton, WA 98055 full output when triode connected. 3-(a) View of vacuum triode and (b) inter-electrode parameters of the triode Table I-Technical specifications of triode 3CW30,OOOH7 Type Filament Voltage Current, at 6. One grid tank capacitor 502 is mounted close to the grid and filament connections of each PA tube to keep the grid-filament RF circuit short in order to prevent the possibility of parasitic oscillations. The primary purpose of these resistors was to block parastic oscillations (squealing) and radio frequency interference in the output stage of the amplifier. If you have an older model AL-811H which does not have these design updates, I urge you to install them, or send the amp back to Ameritron for rework to current specs. k. This must do modification is detailed at item 4. Freced— ing the modulating valve is a voltage amplifier (V-5) for the purpose of raising the level of a dynamic type microphone (impedance 50 ohms) value for adequate excitation of the modulating valve (V-4) The modulating voltage developed across a modulation choke (T—4) is Matt describes the design and construction of the 4S Universal Tube Preamplifier. A DC of 30 to 40 V is sufficient for the tube to draw 400 mA as the grid is connected to the anode. Filament Tap. Actually, it is best to use a driver that is capable of 100 watts p-e-p, to assure that sufficient driving power is available on 21 and 28 MHz, the frequencies at which the efficiency of coupling circuits is In a grounded-grid amplifier, the grid appears to shield the input from the output. 5 volt DC supply could be used here, less the resistors. The input resistor provides a constant value load for the exciter to work into, and there is no requirement for a filament choke and associated pi-network. Reduces interelectrode capacitance between control grid and plate making plate efficiency about 10% greater than a triode amplifier limiter output resistance input Prior art date 1953-06-22 Legal status (The legal status is an assumption and is not a legal conclusion. 13 stabilizing the amplifier 76 Recommended Air Socket for Grounded Grid SK-1320 The EIMAC 3CW40,000A7 is a ceramic/metal power triode designed for use as a high power RF ampliﬁer for indus-trial and scientiﬁc applications. ElectraPrint sells quality filament chokes for 2a3 or 300B. Here we have a grounded grid 304TL running on 80M, 40M, and 20M using the technique just described. The screens typically take around 5-10mA each, and the preamp tubes draw about 1-2mA or so (for the typical 12AX7; 12AT7's are usually biased for around In a grounded grid amplifier using a triode vacuum tube, the input signal is applied to: brought through a filament choke. 7MHz resonant plate load at frequencies below resonance, is inductive. You definitely want to avoid the filament current ground introducing hum in the output stage so you want to keep the three star ground points separate. 3V) filaments are wired in series and driven by the 12. The following illustrations show the structure of a directly heated thoriated filament valve of the 1920s-1930s (similar to a Mullard ORA), compared with a 8-22C4 A logarithmic IF amplifier is preferable to a linear IF amplifier in a RADAR receiver because it: A. Such a complete amplifier works only one tube: The 20B. E. 8Mhz. Cathode-Driven Amplifiers, Grounded-Grid Ampli-. Since the input is to the filament, coax could be appropriate. He comments "I have a particular love of the 807 as an audio valve, so here is my simple grounded grid amplifier. Filament chokes: A choke in the filament line is an absolute must on a "directly heated" cathode, but on an "indirectly heated" cathode such as an 8877, it is not always needed. I think there is a very real possibility of filament breakage over the service life of these tubes if you don't limit the inrush current somehow. The electrons are accelerated down the column through a hole in the anode, which operates at a high positive potential (generally 15 or 20 keV) with respect to the filament. Install the circuit board. No iron anywhere in the audio path use of a large resistive plate load. 17th edition, by Bill Orr comes the closest with a grounded grid circuit that allows for General Description of the Coleman Regulator for Filament-Heating. The cir cuit worked, but the results were only fair. The pair of Chinese 845's were the tubes used to design and test the amplifier. A grounded plug was used, this is critical for safety. Notice the grid's position BETWEEN the cathode and anode. The term most commonly applies to a three-grid amplifying vacuum tube (thermionic valve), which was invented by Gilles Holst and Bernhard D. -3 o plate gridi filament plate grid, filament o- 0-5 milliammeter plate. Th. dia. A twisted pair of wires run from the rectifier socket to the right-hand 6AQ5 socket (figure 23). Blower protection fuses for operator safety, as blower is not switched by amplifier off switch. To give some idea of the scale, the tiny tube on the left (by the multimeters) is a 12AT7 double triode, the larger tube on the right hand is a 3-500Z, a modern 500 watt triode. This will extend the life of the 6AF11 tube. The purpose of this article is to present and review each one of them. Driver tubes are cathode biased with a 1. The simplest vacuum tube — the triode — is made up of 4 parts — the plate, the grid, the cathode and the filament. Instead, use a separate cathode choke. Later the idea occurred to try this method of exciting the tube as a linear amplifier. May 15, 2015 (A) In higher frequency applications r. Within the last few years, the grounded-grid mode of operation has become popular because an amplifier of this type is s mple to bui'd and stabilize, and also because commercial s. The most prized of these tubes put out only a watt or two and sound spectacularly musical through a high efficiency speaker. In its factory configuration it uses a single 3CX1200A7 (triode) tube, grounded grid configuration. To avoid this, the tetrode was invented, having a second grid (the screen grid) between the triode grid (called the control grid in multi-grid tubes) and the plate. RF Amplifier. Drive levels are modest at around 25 - 30W pep. 8-22C5 The high-gain IF amplifiers in a RADAR receiver may amplify a 2 microvolt input signal to an output level of 2 volts. The net result of this circuit is a hum producing voltage induced into the grid unless all capacitances are exactly equal. 9 protection 65 3. The triode’s internal resistance is its saving grace and makes a triode an inherently linear amplifier. Notice, in figure 210, that the grid is like a screen between the filament and plate. " Photo of tuned input used on the G2DAF amp by From one of my receivers. The high-Mu grid in this tube provides excellent isolation and permits stable operation as a grounded grid linear ampliﬁer in class AB or B. Feb 7, 2020 The 12B tube is in the family of 20A, 20B, 30B. 3 volts to power the 6V6 tube. See full list on robkalmeijer. A small-core common mode choke can be tried instead, since the current float is opposite directions. tuned input in a grounded-grid amplifier, filter reactance interacts with the input reactance in the tuned input. But if you use the tube as a plate detector, it should be a sharp cutoff style. It can be used as a medium gain driver tube, or as an output tube for smaller amplifiers, This amp uses a single 3CX3000A7 ceramic triode, in grounded grid configuration, and there is a The filament chokes and transformers are Peter Dahl. B. The side of the choke connected to the If the grid resistor opens, the grid no longer provides a grounded barrier that shields the filament from anode voltage. The drive method here is a grid / choke drive in consideration of the grid ion current effect mentioned above. In the 90's, Ameritron added MOV's from the filament wires to ground near the filament choke bypasses. The plate circuit of the driver is tuned to resonance, which is indicated by a dip in the driver plate current or by maximum d-c grid current in the amplifier stage. 6 The Grounded-grid (Grounded-base) Amplifier ** Fig. No, you don't need DC filaments! The filament is powered directly by AC from the power transformer in your amp. grid thorough Shielding input and output for grounded-grid and is a ring plat. cathode. Output stage. The linear amplifier operates in a grounded-grid circuit. Although there was some amount of current through the grid, it was very small; much smaller than the current through the plate. bronze fingers and an Eimac center filament bushing, so the associated socket was the result. Best 73s, A 1mH choke that can withstand 3A needs a lot of iron; sich chokes are heavy, big and pricey. Pins 1 and 5 are the filament 2. H. This tube features a filament designed to operate at 5 volts, a value that is common to other power grid tubes and allows a single 3CX1500D7 to replace two 3-500Z in many applications. Apr 19, 2020 The answer depends on the triode's amplification factor (mu), use a constant-current source and choke to isolate the filament from the Aug 22, 2016 I wonder, shall I ground (connect to chassis ground) one end of the 6v In that schematic, both triodes are run without grid bias or any The point of having a 0. 4 NEUTRALIZING GROUNDED-GRID AMPLIFIERS Constant current curves for a zero-bias triode with a µ of 200 6. But we have good reasons to consider the tetrode as a cathode-driven performer in its own right. Has a lower noise figure. Consequently, the grid bias for the 811A is: V=0. The heater in the tube, of course, is hot and can source electrons, just like the cathode. Depending on the tube type, they can be used as driver tube, pre-Amp Output, Head Phone, or low output speaker amplifier. The first view shows the mains transformer and two HT chokes ZA44291, plus the LT filament choke ZA44292, on the right. The issues involved in making this selection include circuit simplicity, balanced performance under small- and large-signal operation, and achieving low output impedance (and Voltage is adjusted by paralleling the first choke with high-power resistors to push the filament voltage above 10V in operation. If the filament voltage is much higher than 6. One amplifier with dual 811s has this large bifilar choke in the filament line. However much more interesting is the other end of the tube - the filaments (which double as cathodes) are connected to a direct AC filament heater transformer which means that there is an additional modulation at the 60Hz mains Grounded Grid Following a number of reader enquiries, Graham noted that there seemed to be very little published on the internet on the subject of grounded grid amplifiers in audio. #20 gauge Type-WL high-temp electric motor rewinding wire will carry 5A with ease and it has excellent RF properties. over a wide range by varying the grid bias. Heath W3-AM. Take two 100 ohm resistors and attach them from each side of the filament supply at the pilot lamp to ground. - Blower delayed stop, after amplifier switch off ~ 3 minutes, to evacuate accumulated heat in tube. Only then were the tubes fitted to the amplifier and the filaments run for around 10 hours before HV was applied. Listening to the 26 is a fantastic experience. Cut this wire off from the pins to ground. , JMI used a wire from pins 4 & 5 to ground to keep the filament supply grounded. Grounded-grid operation is attractive flexible leads on the base for grid and filament An Economy Grounded -Grid Linear Amplifier A Pi- Network Amplifier for C -W 673 30 -3 General Purpose Triode Class 30 -4 A 10 -Watt Amplifier- Driver 30 In a grounded grid amplifier with directly heated tubes it is necessary to isolate The filament voltage for the 572B is taken directly from the 6. The grid bars of the second grid are mounted behind the control grid bars as observed from the cathode surface. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Multi-purpose. I have changed that tube for an 3CX1500C7/ 8938 which is a rugged coaxial base power triode designed for use as a cathode driven. 3 volt filament connection, (2) the grounded-filament and B - connection, (3) 300 to 325 volt B + for the exciter stages, and (4) 450 to 600 volt B+ for the final amplifier. PHILIPS , EL6471 , QB3. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed. The choke should offer sufficient impedance to elevate The AL-811H is a grounded grid linear amplifier developed by resistance and impedance, filament choke resistance, and filament wiring resistance. The tetrode is a four-element tube with two grids. 3) exposure switch is depressed to start exposure. Tuned input networktunes out reactive (C) component, and also linearizes tube input impedance via flywheel effect. Filament caps are located in the raised box with the four filament chokes bolted to the top. A few years back I went down the path of exploring different DHT in pre-amp stages for sonic improvements on detail and dynamics. electronics in 1988 -- the newsgroup was connecting the control, or number 1, grid to •5518 Lincoln Blvd. This operates as a grounded grid RF amplifier stage and thus suits a low impedance input. It is DC isolated from ground, (RF grounded thru two 1000pf The purpose of this page is to present the full unedited Eimac Filament Management program to readers as applicable to amateur radio amplifier systems, and to show proper filament voltage measurement techniques before people injure or electrocute themselves, diminish amplifier performance, or damage tubes. 5Volt for all 4 tubes. Originally designed as power triode for UHF Radar applications it has a plate dissipation of about 1500W. amplifier features fast warm up and 1500-Watt RF output with 100-Watts of drive. Thus providing a speaker output, and a normal signal input. Then supply a "high voltage" of about 35 V and set the voltage to a current of 400 mA. Rinaudo, W6KEV A High-Power Amplifier and Power Supply triode mode with Ia = 25mAdc and with fixed grid bias and fed with Idc to anode from CCS from B+ may measure 1,400ohms, 1k4. Amplifiers that connect the drive to the grid don't have filament chokes. The heater in the tube is powered by filament wiring coming from the power supply. Rules for Setting Filament Voltage grounded-grid circuits. It is purpose designed for 2 3CX800's and also has the 13 volt 3CX800 filament supply. The unit is a completely self-contained table top unit capable of 1000 watts input. filament, two grids, and a plate (thratron) rk-6i and xfg-i are triodes. The impedance of the 10. 5 volts which is still pretty bright. Anode) has a positive voltage applied to it. There are a total of 3 separate power supplies that are all turned on by one switch. This is done to maximize power output from the tube, but it is not necessary for demonstrating basic operation. wear out as their filaments (and some- times other parts) deteriorate use the circuit board traces themselves driven (grounded grid) amplifier as. Proper method of grounding Dentron GLA1000 Modifications Tuned Input for the Grounded Grid GS-35B triode. The flow of anode-cathode current is controlled by the voltage which is impressed between the grid and cathode connections thus, if the grid is to be earthed, the The cathode choke for the 4P1L is of TC60-35W (60H/35mA, DCR: 730 ohm) ex-Tango which was originally designed for the plate choke use (for the small power tube use). 5V @ 1. Some of the nice features of this amplifier include; Peter Dahl transformer. LC Limited Connec- tion-Do Not. The grid bias voltage is 1. Loop Bias explained. Always double-check your work first. In the 1950’s and 60’s , Philips in Holland produced a number of pro-use amplifiers, spanning from 2-4 channel pre-amplifiers to small, medium, high , super high and extremely high power amplifiers. TRIODES ratinded. Figure 209 shows the construction of a triode. 10 keying 70 3. 5", Mu=125 rod, 3" long can be used to make such a filament choke. All that existed was the power supply and the amplifier chassis which contained a 4-250 tube, an RF choke for 27 MHz, a filament transformer, several meters, and the cooling system for the tube. A Compact 3-500Z Linear Amplifier . By loading a triode voltage amplifier with a high impedance, Bottom View Showing Tube Sockets and Filament Choke The amplifier uses a conventional grounded grid design. The input in parallel in a grounded-grid configuration. 024 x 730=+17. also a good source of 300 pf variable caps and I think a slightly smaller I realized in 1976 a 144 MHZ amplifier with a 4CX1500b. 5—AMPLIFIER CONSTRUCTION An 811 A 200-Watt Grounded-Grid Linear Amplifier . The SEA-1 amplifier is a straightforward single-ended audio power amplifier that delivers about 11 watts, using only medium and low-mu triodes. If you use a filament transformer with a center-tapped output, ground the center tap and eliminate the 220 ohm resistors. The black tar that comes out of the overheating transformer makes an unpleasant mess inside the amplifier. Idle Current 150mA. The 5V phasing must be correct, the easy way to test this is to try both orientations and monitor the 6. Why Should I use a Coleman Regulator to heat my directly heated triodes? across the filament causes corresponding changes in the grid-cathode voltage. In a grid-driven Class AB1 amplifier, The RF-grounded screen appears to shield the input from the output. I chose instead to use some 12 VDC fans, which pressurize the final compartment, and provide better cooling. Only half that amount is needed to drive its class-ABI Ameritron AL-1200 to GS35B Conversion. 3V, it would be a good idea to trim the voltage with a small dropping resistor in series with the filament winding. Except for 6. The grid bars of the screen grid are mounted directly behind the control-grid bars, as observed from the cathode surface, and serve You will notice on the amplifier schematic that both triode elements inside the 12AX7's glass envelope are being used, in parallel: plate connected to plate, grid connected to grid, and cathode connected to cathode. RCA 1933 AN-5 Application of the 79 Tube - A push-pull class B amplifier for automobile radios. In short, to make a 300B power amplifier, use AC filament, cool transformers and good tubes with high quality capacitors, and a large chassis. Heat the tube 30 minutes with a filament voltage of 4. I explored all sorts of different DHTs as have posted in the blog and many more I never got around to write up about. Indirectly heated tubes have a cathode sleeve around the filament heating it. Bottom of the RF Deck showing the G3SEK Triode Board and Tuned Input Box . This tube features a filament designed to operate at 5 volts, a grounded grid circuit to insure simplicity of design and measure the filament voltage at pin jacks on the back panel of the RF chassis. has rugged. 3 volt leads from the transformer are attached to pins2 and 7 of the same socket. a. does not require the use of filament chokes. The output of 2A3 (C) driven from the first stage tube is obtained from 3 W to 3. Try it again with the output tubes installed. and there is no requirement for a filament choke and associated pi-network. 5 lead lengths 58 3. The filament choke is near the bottom. The side of the choke connected to the In a grounded grid amplifier using a triode vacuum tube, each side of the filament is connected to a capacitor whose other end is connected to ground. If you do not know anything about how vacuum tubes work, you might want to read the sidebar before reading further. Wolfram grids allow the most precise grid wire distance, because wolfram is an extreme hard metal. 5", All the hybrid amplifier use as voltage amplifier vacuum tubes and transistor or D3A specifications in triode connection: filament current: 315mA Tuned Input for the Grounded Grid GS-35B triode. employing a beam tetrode valve (V—4) as the power amplifier. Grid Current 260mA. 12AY7 is the type of tube and it's really two tubes in one (dual triode). TANK CIRCUIT. No negative feedback is used, other than local cathode degeneration. A 4-400A requires 40 W of drive power for '18754 130th Ave„ S. It serves as the second-amplifier stage and also as a diode rectifier to supply the AtvIC bias for the grid of the 12BA6. . There is room for a large power supply cap if you want one (to the left of the volume control), although it doesn't seem to make much difference. The control grid is the common element in the two circuits, and they are only coupled by the common electron stream within the tube. The pentode consists of an evacuated glass envelope containing five electrodes A good example of a valve with a directly heated filament cathode is the 300B triode, manufactured since the 1930s and still in use today (we will discuss the triode in more detail later). Designed for general purpose or replacement use in push-pull tube output circuits. Tellegen in 1926. When tube manufacturers state the cathode driving impedance in grounded-grid operation, they are talking about an average value. I use a Lundahl filament choke and 47000uf capacitor in front of your regulator. RF chokes are used for plate and cathode loads. Frequency response: 150 Hz. long) isolates the cathode and filaments of the 3Cx800A7. A triode is an electronic amplifying vacuum tube consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode). This does not mean the tube works just like a 1k4 resistor. The detail and colour of this stage is unique. C. 1) kvp/mAs is chosen. cylindrical filament-stem linear filament tank for V H _ F. operation of capacitor discharge unit in mobile xray units (4) terminates the exposure. The Viking II leaves the suppressor grid grounded and supplies B+ to the screen through a 22K screen resistor. A triode has three electrodes, a grid, cathode and plate (anode). 3 V ac The AL-811 is a grounded grid linear amplifier Relay: keys amplifier when grounded. Feb 15, 2017 A 211 SE Triode Amp 845/75TL Single Ended Amplifier . I was the Chief Engineer and I sure do not remember using a > triode > > in the amplifier a > > >filament choke. Predicting Distortion In a graphical representation of these three qualities, gm rp and mu, as they vary with plate current, gm rises markedly with rising plate current, rp falls proportionately, and the product remains virtually constant. Cathode choke RFC1 provides DC return path for plate feed, and allows cathode to “float” at RF potential. The grid is the 'control valve' that controls the flow of electrons through the tube. heater (filament) A pentode is an electronic device having five active electrodes. a coupling capacitor with a safety RF choke to ground at the output. , are on the Certificate that is on the outside of the tube box. The only ground connection for the filament circuit comes from the center tap between the two 6AU6 tubes, this provided the lowest hum. Pentode circuit showing the parts of the tube (inside the circle) and the signal path. Operation with zero grid bias in many applications offers circuit simplicity by eliminating the bias supply. The grid always operates at around zero voltage anyway, so plug in what you have. The 57 is a directly heated pentode, the G3 suppressor grid is connected to the center of the filament. 3. This signal is equal in amplitude and opposite in phase to the signal fed back through the plate-to-grid capacitance, thereby canceling this feedback signal. dot is gas multiple cells or a battery fixed resi stor r. Amplifier Wiring The filament wiring should be done first. It could be attached directly to the chassis for grounded grid or mounted below the chassis with small insulators for a conventional grid driven amplifier. Power it up without any tubes plugged in. Has a greater dynamic range. Build or buy a cabinet. nl In a grounded grid amplifier using a triode vacuum tube, each side of the filament is connected to a capacitor whose other end is connected to ground. long, 3/4 in. The dual-triode grids are connected directly to the signal input. ode (i. Another view of the bottom showing input cover in place and HV wiring attached The passive grid configuration has a couple of advantages compared to a grounded grid design. Complete the Amplifier Startup Procedure. The CT of the filament winding ties to the star ground point. Provisions are made for an external bypass capacitor from the B+ side of the output transformer to the output tube filament (ground). Although there are a number of different types and arrangements of the triode (see figure 210), they all place the grid between the cathode and the anode. 5/750 PP , 1955. grid* grid3 The RE604 output stage is biased the same way as the previous amplifiers, however the grid is AC vice ( Read: signal ) strapped to a grid choke. For the directly heated triodes, filament supplies have long been problematical. 3 typical rf amplifier circuit designs 52 3. unique grid- and filament-terminal arrangements. Jim Mueller _____ 10: The Grounded Grid Amplifier. All grids I connect to the anode via Kiwame or some other low value CC resistors. First, the drive requirements are reduced. The electron gun is of triode design, with a tungsten filament, a grid cylinder, and an anode. You will notice on the amplifier schematic that both triode elements inside the 12AX7’s glass envelope are being used, in parallel: plate connected to plate, grid-connected to grid, and cathode connected to cathode. During normal amplifier startup a 150 watt light bulb's filament will glow bright red as the amp's capacitors are charged, then dim as the amp's power stabilizes. Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode, the triode was the first practical electronic Safety Code 6 sets limits for contact currents that could be drawn from ungrounded or poorly grounded objects (33% chose this) D. This is the "textbook example" Williamson amplifier with an ultralinear output. A tube with only one grid is a TRIODE. filament frequency conductor grid Prior art date 1950-08-29 Legal status (The legal status is an assumption and is not a legal conclusion. Right, that brings us to the weird “loop bias”. The grid current for the 811A is 12mA in resting condition, so that actual current through the choke is 36-12=24mA. 6A131 - What is the primary purpose of the suppressor grid of a pentode? A. Intense-cooling technioues are applied to the copper anode structure for the purpose of providing high The circuit uses output transformers and a sophisticated full valve rectified, choke smoothed, regulated power supply including a 300B triode as the series element. The GS-35B amplifier requires a driver that can deliver at least 80 watts p-e-p. The input impedance is 100 kΩ. During neutralization, a "dummy" tube (one without filament Fig. PICTURE 4 above. A negative voltage applied to the grid with respect to the filament would tend to choke off the natural flow of electrons, whereas a positive voltage would tend to enhance the flow. ). With this circuit (grounded grid triode amplifier), the cathode is the input. Plate-to-grid capacitance transforms this inductive load below resonance into a negative resistance at the grid. Output Circuit: The amplifier output circuit is a common pi-network. A semi-remote cut-off tube is used in this stage rather than the conventional sharp cut-off pentode to allow smooth distortionless AMC action. transmitting tubes in grounded-grid linear amplifier circuits. When the tubes are plugged, the filament voltage should be very close to 6. it is filament A' a result of the use of install or remove without the aid Of tools. 6V supply. Reduced ratio (6 to 1) vernier drives on all tuning controls allow smooth and easy tuneup. Each tube has an anode dissipation of 500 watts, 20-Watt grid dissipation and plate voltage up to 4000 volt. This has two anodes which are wired together as a single-phase rectifier in the circuit shown above. Has higher gain. FILAMENT BY-PASSING 60 5. 2. control grid. The circuit of the amplifier and power sup- ply is shown in Figure I. 11 amplitude modulation 73 3. This way you can check the various secondary voltages. This is critical to the sound of the amplifier, starving the filaments will kill the dynamics of the music. First is reducing ripple voltage to the filament. 015 inch. f. And it must be quiet in both common-mode and differential mode, a distinction that is often neglected. One example is J. In a grounded cathode gain stage, the tube will amplify any signal it sees between the grid and the cathode. The circuit below shows two stages of a triode valve audio amplifier. HPB you are correct in that the switch is not working. This kit, along with the capacitor/rectifier kit is a good way to modernize your Heathkit SB200/201. 5-kΩ resistor, and 145-V plate voltage. The Ameritron AL-1200 Amplifier is in current production. Best sounding 2A3 Single Ended Tube Amplifier Single Ended Triode Stereo The 45 is a filament type triode power amplifier designed for service in the An introduction to ferrite and chokes, and how to use them to stop RFI bias and metering cir- cuitry 's conventional for a grounded grid amplifier. W. The input circuit consists of a coaxial coil made to offer 50-Ohm impedance at 52. Triode "inverted" operation, that is, use of the control grid structure as the anode, and use of the plate structure as control grid. This grid is connected to a positive voltage close to the plate potential, but grounded to high frequencies through a decoupling capacitor. The attached image is from a W6SAI Radio Handbook, printed in 1951. Many radio amateurs have used this beast as a power triode in HF linear amplifiers in typical grounded grid configuration. 5 W. High-transconductance twin triode designed for use in VHF circuits as a cathode follower, grounded-grid amplifier, or frequency converter. The filament takes a massive 18 amps at 17 volts although the only slightly suitable transformer I have drives the heater to about 15. It is simple, the entry level is not high, everyone can build it without exaggeration. The filament transformer outputs 12 volts AC to power the filament on the 12AX7 tube. For details of the effect, please refer to the explanation above. Grid- anode spacing is 0. The classic cathode driven or "grounded grid" circuit is used. choke (RFC2) in the filament circuit iso- lates the filament transformer. 6V supply, the two 6AU6 (6. Power flows in series through the light bulb filament and then to the amplifier. DOUBLE. Prior to fitting them to the amplifier, all the socket’s grid pins were grounded to chassis. tub. The 2A3 tube is called a directly heated triode (DHT) which means that the filament also acts as the cathode. 4 uH, 10 turns on 1/2 in. With plate Class AB1 grid-driven amplifiers look more complex than Class AB2 grounded-grid amplifiers. Safety Code 6 sets limits for induced currents, electrical field strength and magnetic field strength from electromagnetic radiation (9% chose this) In large tubes having directly heated filaments, the mains frequency filament supply voltage will appear in the cathode (filament) to plate circuit, so some precautions against hum injection are essential - usually a grounded centre-tapped filament supply is adequate however some designers prefer rectified and filtered direct current. 5V These triode tubes are found mostly in grounded grid amplifiers. The RE604 output stage is biased the same way as the previous amplifiers, however the grid is AC vice ( Read: signal ) strapped to a grid choke. In conventional "Pentode" configuration, the Suppressor-grid is directly connected to the Cathode either internally by the tube manufacturer or by the user. e choke 5 voltmeter ma duo or dual 2 triode sect- ions in glas envelope pentode 5 elements; filament, 3 grids and a plate grid grid. 3V. A triode valve when configured as a grounded cathode amplifier suffers from one major drawback. It makes a good display Completed amplifier. To date this amp is still in Contests operation. The grid capacitance of tubes that are commonly used in Class AB1 grid-driven amateur radio power amplifier service ranges from about 15pF to 130pF. Then put on some safety glasses. working amplifier based on a high vacuum triode around 1916 – he named it ”The The “retardation coils” = chokes are meant to isolate the filament 5. 75A Pin 2 is the plate, pin3 is the control grid G1, and pin 4 is the screen grid G2. The AC guitar audio signal charges the grid positively and negatively as it alternates. A filament transformer was wound that could be used with the socket. /ed B employing a beam tetrode valve (V—4) as the power amplifier. This provides very low "plate resistance", making output transformerless single ended operation feasible. never been able to use an open-frame relay socket with the filament choke in place The plate load choke also isolates the output stage from the power supply. Is more easily aligned. and impedance, filament choke resistance and filament wiring. Filament Choke - AG6K - "For a HF application, Triode Tube Design. The cathode lead can be grounded as a filament tube would be, or components can be connected to that lead. Use, Except AI>. There are various opinions and solutions how to do it, but with a 3-500Z it can be relatively simple. A High-Power Linear—Floyd K. ref. The filament uses 2. THE AMPLIFIER CIRCUIT. Thermionic emission from the heated filament is the source of free electrons. At all frequencies other than the IF, the grid is loaded. This is a broadband circuit (beyond 40 to 60 MHz. In large tubes having directly heated filaments, the mains frequency filament supply voltage will appear in the cathode (filament) to plate circuit, so some precautions against hum injection are essential - usually a grounded centre-tapped filament supply is adequate however some designers prefer rectified and filtered direct current. 4 component parts 57 3. Filament chokes are used in grounded grid amplifiers. Topic of this particular trivia quiz was "general, pre-microprocessor electronics" when posted verbatim to sci. The 3CX2500A3 may be. core, 2 in. Note that the filament A typical circuit configuration for a grounded-grid amplifier using a filament choke is shown in Fig. F. The input network is a T-network, with two inductors (8 turns, 1 in. type, is front panel switched for measurement of the plate current of all other r. (I. (For single ended use, see our 125 SE series - optimized for single ended tube output circuits). TYPICAL CATHODE DRIVEN (GROUNDED GRID) AMPLIFIER CIRCUIT FOR TWO 3-500Z TUBES Direct lnterelectrode Capacitance (Grounded Filament) This amplifier uses a pair of 813 beam power pentode tubes. Freced— ing the modulating valve is a voltage amplifier (V-5) for the purpose of raising the level of a dynamic type microphone (impedance 50 ohms) value for adequate excitation of the modulating valve (V-4) The modulating voltage developed across a modulation choke (T—4) is Another good source of parts is the old ft 101 series radios. This is a very beautiful tube having a brightly shining thoriated-tungsten filament with plain plate encapsulated in a large-size perfectly transparent glass tube without getter. 8 grounded-grid circuits 63 3. On the back of the chassis is a four-prong socket to which are supplied (1) the hot 6. 1) is a filament current has to be fed into the cathode by high current RF chokes, (cathode driven, both grid and screen grounded) What is the gain in dB of the stage Hi Tom, what will you use for the filament choke? Henry 8K is a ham radio amplifier that uses this tube. Start studying IFC_ELEX_Q&A_3. The high-Mu grid employed in this tube I've been hoarding parts over the past year considering building a linear amplifier using vintage parts & design. 7 screen and suppressor grid by-passing and screen tuning 62 3. the cathode and the filament are the same tube element) and are designed to warm up instantly. The same is true for 2A3 245 71A single-ended amps. The circuit used is a classic two stage amplifier. The fan has high quality bearings and will last a long time. 9 V. The tube doesn’t particularly care if that is an audio signal or an induced signal from some other part of the build. They use the same inexpensive socket. Figure 4:. The net voltage at the plate of the triode is only around 550V DC which is consistent with a choke smoothed circuit. As with most all tubes, there is an input and output circuit. If the amplifier has a short circuit the light bulb will light up to its rated brightness. Mount the speaker into the cab. attributes of grounded-grid operation can grounded-grid circuits. I figured that this would make the start of a nice linear amplifier for the 600 Meter band. 4 NEUTRALIZING GROUNDED-GRID AMPLIFIERS Reactance of an RF choke vs. A low cost 600 watt ultra TUNED INPUT ADJUSTMENTS FOR GROUNDED GRID TUBES Leave tubes Mu=125 rod, 3" long can be used to make such a filament choke. - Grid 1 PTT control via fast switching relay ( 7/3 ms ). ) On my 300B and 6C33C SETs, all triode mode pentode drivers sounds more comfortable and relaxed. In keeping with the past tradition of the HL500 and HL750 series amplifiers, only the highest quality components were used in the design of this Grounded Grid Following a number of reader enquiries, Graham noted that there seemed to be very little published on the internet on the subject of grounded grid amplifiers in audio. Finish the amp, install faceplate, knobs and insert the chassis into the cab. The secondary of the filament transformer is isolated from the vacuum tube with a homemade bifilar choke wound on a 1/2" diameter six-inch long ferrite rod. The model number is 6107A (not 61V07) and the grid-cap tube is a "57". The 12AT6 stage fulfills a dual purpose. The use of the grounded grid amplifier using triode valves (Fig 10. At the time, I was inspired by the realization of our friend Daniel F1DRR (SK) with some modifications. Input impedance of grounded-grid triode amplifier Is low, complex, and also non-linear (decreases at onset of grid current). This amp is not the only grounded grid tube amp that needs this protection; it has become a problem, due to inferior tubes of today. In 2003, I decided to build another amplifier with a triode GS35b for the 144 mhz. Data for the 8938 are the same as for the 8877 but the coaxial base is more suited for VHF/UHF operation. It is similar to the 8877 triode in Triode neutralization is used around the first FM-IF stage.