cathode follower circuits

The biasing of the gain stage is not particularly important, and follows normal conventions. Designing the Gain Stage The first two design considerations are the 6922's the plate current and plate voltage. You can make a cathode follower have gain (they don't sound very good), but here's the skinny: Paraphase. Regards, Larry. The second schematic is a simplified version that can be used when the following tubes have no grid current. Most other circuits use a series connected output stage, with either a single or push-pull input to this stage. These circuits can achieve very low distortion and output impedance as well, but suffer from the same issues as a cathode follower output stage. Cathode follower. This voltage swing will be roughly the same as the grid, but the current swing will be larger, ideal for the low impedance tone stack (meaning you loose lots of current to ground in it). Kemper profiles, from own circuits designs. A cathode-follower power output stage is driven by a novel drive stage to provide with low distortion the large signal required to drive the output stage. The output is also in-phase with the input. However, it does exhibit Buy Transistor IRF820 N-Channel MOSFET 500 Volt 4 Amp TO-220. Long Tail Pair According to the Cathode Follower calculator, the voltage gain for the DC-coupled cathode follower is near unity (-0.1dB) and the output impedance is a very low 615Ω. Figure 14 - Valve Cathode Followers. « Reply #35 on: December 12, 2015, 04:00:12 pm ». Fortunately, cathode-stopper resistors can usually be quite . The load Rl. Two stage 12AU7 preamplifier with low impedance output stage. Cathode follower design (amp and modulator needed) I need a cathode follower circuit that can cover from 75KHz-16MHz using 1/2 of a 6SL7. This means that the cathode resistor is tied to a more negative voltage of something more than twice the bias voltage, so it can pull the output tube grid negative. An IRF 820 has both enough voltage rating and more than enough current and power ratings to do the job. Input is fed to the grid, and output is taken from the cathode. Dave Hecht 12ax7 cathode follower is pretty common in guitar amps. Last Updated on Tue, 01 Jun 2021 | Electron Tube Circuits. However, in the latter voltage amplifier circuit, a signal level where distortion occurs is lower than the cathode follower circuit case, and thus a . One issue is the use of cathode followers, which are used heavily in these designs for speed and for driving the low-impedance diodes. A cathode-follower power output stage is driven by a novel drive stage to provide with low distortion the large signal required to drive the output stage. Sozo Blue caps were used to modify the overdrive circuit (and other parts) making it smoother and more bluesy, more like the Fender Bassman tone stack with a Bassman/Marshall cathode follower circuit. This circuit is normally used to drive a coax output (low impedance). Circuit #3. The cathode follower (officially known as a common anode circuit), like the common cathode, takes its signal at the grid, but the output is taken at the cathode, not the anode/plate. It deploys two triodes: the first generates the required voltage gain while the second acts as a current amplifier The preamp circuit in these blackface amps, and the tone stage in particular—which also evolved into the silverface amps of the late '60s and '70s—was an original creation from Leo Fender and co., and very different from the cathode-follower stage of the tweed amps (as discussed above). The cathode resistor for the second stage voltage amplifier is not bypassed by a capacitor, creating negative feedback from cathode degeneration. Input impedance. The cathode follower (officially known as a common anode circuit), like the common cathode, takes its signal at the grid, but the output is taken at the cathode, not the anode/plate. Midrange gain, from the grid of the voltage amplifier to the grid of the cathode follower, is therefore 37.8dB. The other is the cathode-follower output from the 6V6. The Overdrive circuits boasts a separate OD bypass cap 0.68uf that is exactly a Marshal spec. The cathode follower is often used in this 'buffer' configuration specifically to provide low output impedance. In the cathode follower you use the the voltage swing across a resistor between ground and the cathode. You will need double the heater current. The author of the article used a cathode follower circuit ahead of the grid leak detector to isolate the detector from the tuned circuit to counteract the grid loading. A constant current source IC (10M45) is the load for the driver tube, and an FET source follower is the current amplifier (replacing the cathode follower). Often the driver can't keep up with this reactive swing leading to distortion. The first version with E82CC/5814 should be considered the starting point. The board on the left is the logic board. Both are effective for DC but only the 2200 ohm sets the output impedance. As discussed, the cathodyne can't work as expected until its input is below 1/2 of B+, and doesn't get "right" until 20%-35% of B+. Tubes have a maximum heater to cathode voltage. I'm looking to build some digital logic circuits using vacuum tubes and germanium diodes, as was done in the 1940s and 1950s. The AC signal floats on the DC value of the cathode. Anode follower. 6-8. The White cathode follower may have an advantage in gain bandwidth over the conventional cathode follower by a factor of five. So what makes this circuit so interesting? The overall gain is about 8 times. The plate current is selected at 8.5mA and plate . The 12AU7 contains non-linear triodes. Note that the same number of resistors is used in both circuits. You want to buffer a stage from the circuit which follows it (perhaps cable capacitance from the output of a standalone unit). This reduces gain and increases output impedance. Also a 1 meg resistor connected to the grid is in series with a . The second circuit used in the module is the cathode follower, which is essentially a buffer; its low-impedance output let it drive other circuits. But suppose I have a circuit that's functionally similar, but in which *every* voltage gain stage is followed by a DC coupled cathode follower (including each side of the splitter). One of the circuits, using only Z$ double . There are two features that give this amplifier its superior performance. It is the simplest buffer that can be made with tubes: one tube, one resistor. The output will be feeding a resistor network of a little less than 1K through a .001uF cap. Cathode Follower is irrelative to Cathode Biasing. The output is also in-phase with the input. An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal (a time-varying voltage or current).It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. To put it (almost) simply, a cathode follower is an impedance conversion stage within an amplifier circuit that transforms a high-impedance signal into a low-impedance signal. The SRPP circuit has also been referred to as a SEPP, Totem Pole, Mu Follower, Mu amplifier and Cascoded Cathode Follower. Gain. With minor changes as to how the output cathode followers circuit connections are configured you can drive class A, AB, or B push-pull outputs or even a totem pole output circuit. A) shows a cathode follower with an input capacitor (C1a) and biasing resistors (R1a and R2a), which operates as a stand-alone circuit with an input from any suitable source. In many cases, cathode followers are simply directly connected to the anode circuit of the preceding stage as shown in B). Complete schematic diagram of direct-coupled 6V6 cathode-follower amplifier. The first series of models, is inspired by the tone of vintage amps, but they have they own circuit design. You may need some amplification ahead of the cathode follower to adequately drive a 6146 as a common-cathode power amplifier. Cathode follower has a voltage gain of slightly less than 1, a low output resistance of about 1 KOhm, a high output resistance of about 500 MOhm, and is a non-inverting circuit. The grid leak resistor and the input coupling capacitor are required as before. 333k. If the grounded-cathode Amplifier is the quarter horse of tube circuits, then the cathode follower is the work horse. My favorite for this sort of thing was the 6SN7-GTA dual triode, which may still be available as . Since there is a 1k resistor in the cathode circuit, whatever voltage you measure across the resistor . A cathode follower circuit (as you have here) is a current amplifier, not a voltage amp. M1 is the top follower which provides a fixed DC voltage using the resistor divider formed by R7 and R8. The lowest prices in the industry. The former is a design choice to create the amount of gain desired within the context of system input sensitivity and the stage's position in the . Comparison Of The Cathode And Anode Follower. The effect on the transient respcnse of varying the circuit parameter is discussed and throughout the paper the White cathode follower is compared with the well-known conventional cathode follower. The calculator calculates a cathode follower's unloaded voltage gain (the gain without being connected to the next stage) and output impedance based on the triode's characteristics and the cathode resistor value. Because you are not logged in, you will not be able to save or copy this circuit. The common cathode circuit has plenty of voltage gain, some current gain, and high output impedance. Feedback in Cathode Followers Think of a cathode follower like a grounded cathode amplifier in that the grid modulates conduction through the tube and load resistor. The gain for the above circuit is: Av = 19.5 / (19.5 + 1) = 0.95 Here is a PDF link to the original Ongaku schematic. The former cathode follower circuit can achieve a wide dynamic range of output, that is, the range between the lowest level limited by residual noise and the largest level limited by distortion. All profiles were made using: Focusrite ISA 428, AKG C-414 ,Electrovoice RE-20, Neumann TLM 103, Brauner VMX, SE Electronics RNR1 Ribbon. Re: Cathode Follower Reverb Circuit. The self-biased cathode follower, shown below, uses the voltage drop across the first cathode resistor to set the negative grid voltage (negative relative to the cathode). The cathode-follower section is direct-coupled to the input stage for low phase shift and stability. The drive stage comprises two series connected vacuum tubes which share the large static and dynamic voltages of the drive stage so as to provide a drive signal having a large voltage swing, without generating audible distortion and without . In fact, the tube current source circuit looks much the same as the JFET current source we covered in the previous article. This is plausibly a cathode follower circuit with regenerative feedback. The second most common circuit in use is the cathode follower. This situation is identical to the conditions of the cathode follower and emitter follower. The neat thing about tubes and JFETs is that they can be biased with a simple resistor. The cathode followers are directly coupled to the plate of and bootstrapped back to the driver stage's resistors. For other applications, as Jim mentioned, 12at7 or 12au7 would be a better choice. 2) The reason it was not done with "self bias" (cathode bias) is because it's a cathode follower, and the designers wanted a specific level of output impedance and plate current. The cathode follower This circuit, shown in above, is the valve equivalent of the emitter follower and has the same advantages. Cathode follower has a voltage gain of slightly less than 1, a low output resistance of about 1 KOhm, a high output resistance of about 500 MOhm, and is a non-inverting circuit. The latter is less susceptible to interference and can have a beneficial effect on tone. The headphone amplifier circuits (figures 3a, 3b and 3c) use a single-ended triode class A gain stage and a paralleled-triode cathode follower output stage. In this example, it is 250 Ω. As such, the type makes a poor voltage amplifier. One of the circuits, using only Z $ double triodes, has an input-output voltage . And the IRF820 is about $2.00 each, doesn't need heater current, and won't wear out like a tube will. The current is determined by Vg, the cathode resistor, and the capability of the tube to provide the corresponding current. In a SE cathode follower there is only one tube, and it's cathode "follows" the grid. One of the cathode follower's virtues is its low output impedance, so it seems a shame to raise it by adding series resistance. The 'Hobbydyne' circuit is another way to isolate the detector load from the tuned circuit and doesn't require an extra tube section. The components of the FET circuit show: R o = R s / (1 + g m R s) R o = output impedance (resistance . You should be able to throw together a cathode follower fairly easily. C4 provides the bootstrapping between cathode and anode to force constant voltage operation at all times. The cathode follower has negativevoltage gain: the output voltage is less than the input voltage. This splitter takes the signal out of the 1st tube, passes it through a voltage divider and injects it into another tube to obtain the inversed signal. 2. Earlier research (1-7) about toroidal output transformers has shown that the toroidal transformer is very well suited to function as the impedance converter between the high The higher these are in value the smaller C4 is. US3020486A US712251A US71225158A US3020486A US 3020486 A US3020486 A US 3020486A US 712251 A US712251 A US 712251A US 71225158 A US71225158 A US 71225158A US 3020486 A US3020486 A US 3020486A Authority US United States Prior art keywords cathode transistor circuit tube resistor Prior art date 1958-01-30 Legal status (The legal status is an assumption and is not a legal conclusion. Output impedance. Remember there is LOTS of BS posted on other forums . CiteSeerX - Document Details (Isaac Councill, Lee Giles, Pradeep Teregowda): Summary-Some direct-coupled augmented cathode-follower circuits are described suitable for power-tube grid drivers, coaxial cable drivers, high-input impedance isolation stages, active elec-tronic filters, and frequency selective circuits. This phase-splitter is also called "anode follower" or "see-saw". 1. In guitar amps a cathode follower is most often used in place of a gain stage, it gets its name because the signal is outputed through the cathode instead of the traditional plate output. 10.2.2 Intermediate amplifier with cathode-follower The VOX-circuit (Fig. In general, there are only a few reasons to use a cathode follower: 1. R36 is the tail resistor that creates the relatively high voltage (34v DC in the Bassman) needed for the cathode follower function of the upper cathode. Designing the Gain Stage. Direct-coupled Amplifier.4 It is possible to build a type of cascaded amplifier without reactive elements and, in principle at least, secure a very broad band . The voltage out should be very close to the voltage in (if the grid bias is correct (which it seems to be)). The previous plate is probably at 70% of B+. (The cathode-follower [Figure 24] is of use for coupling a high impedance to a lower impedance level, serving the same function as the emitter-follower transistor circuit.) 1. C gk To a good approximation, Av = μ / ( μ +1), so for an E88CC ( μ ≈32), Av =0.97, Cag =1.4 pF and Cgk =3.3 pF. There is also a 6 Volt heater version with the superb Russian 6N6P tubes. The grounded-grid circuit provides step-up impedance characteristics, paralleling the function of the common-base transistor circuit. On the PC-1T you can have "degenerative cathode feedback", know as local feedback, or no local feedback. The cathode follower has a high input impedance and a low output impedance. This minimises the distortion of the valve. While the schematic (below) looks similar to the inverter, it has the opposite effect since the output is from the cathode, not the plate. The follower is set up so that its cathode sits at the normal negative bias voltage of the output tube, maybe -10V to -40V depending on the tube type. In an application where the follower is driving a transformer or other inductive load this will include a swing below ground into negative voltage. Figure 3b. Summary-Some direct-coupled augmented cathode-follower circuits are described suitable for power-tube grid drivers, coaxial cable drivers, high-input impedance isolation stages, active elec- tronic filters, and frequency selective circuits. As far as I'm concerned the jury is still out that the 12AX7 LPS can not tolerate the higher Cathode voltage from a Cathode Follower circuit. Yes the V2 position on the MAZ is a Cathode Follower which drives the Tone Stack, like most Tweed and Marshall style amps do. May 10, 2017 - A Direct-Coupled 6V6 Tube Amplifier with Cathode Follower by Raymond H. Bates from Radio & Television News magazine November 1949. The first two design considerations are the 6922's the plate current and plate voltage. Backyard Tube Amps. This leads to several differences. The cathode follower does not need a plate resistor because, well, it is a cathode follower. The grid bias voltage is derived in exactly the same way as for other valve amplifiers, by the DC . Note that the cathode circuit has two resistors - one is bypassed and the other is not. What it does offer is CURRENT gain, and is useful for driving current-hogging circuits like tone stacks. Education is what you're left with after you have forgotten what you have learned. Cathode followers can't be easily used . It also supplies a near constant current flow shared between the two cathodes--as current increases through the upper cathode the current decreases through the lower and vice versa. Diode Cathode Follower. You need a low output impedance. The drive stage comprises two series connected vacuum tubes which share the large static and dynamic voltages of the drive stage so as to provide a drive signal having a large voltage swing, without generating audible distortion and without . The input impedance of this follower is equal to the three 1M input resistors in parallel, i.e. Drops right in, drain for plate, gate for grid, source for cathode. Fender, Marshall, Hiwatt, Orange have all used a 12ax7 follower on many of their models. upper tube acting as both a cathode fol-lower and a plate load for the lower tube. Figure 94 (Schaltbild 94) This is the most intriguing circuit in the collection, in that a tuned tank circuit with a grounded centertap is driven on both ends by the . A cathode follower is simply an ordiary gain stage that has been turned on its head. The common cathode circuit has plenty of voltage gain, some current gain, and high output impedance. It has good sound but with some distortion because noval (new 9-pin . The resistor bridge divider imposes a constant voltage Vg on the tube's grid; the tube attempts to reflect this very voltage on its cathode. A cathode-follower stage, biased by a resistor bridge. Cathode follower and directly heated tubes. > direct coupled to the preceding triode stage. 10.2.2) differs from the Fender-circuit not just in the sequence of the partial systems but also in the build of the second amplifier stage. The cathode of the follower will be at about 150V or so, more than enough room to justify sticking in a tube. Transistor IRF820 N-Channel MOSFET 500 Volt 4 Amp TO-220 available at Jameco Electronics. One is direct coupling between the plate of the 6SJ7 and the grid of the 6V6. If you really need line stage gain, the linked PCB will work fine, with 12BH7 s populating the sockets. Given 100% local current NFB, the 'U7 is OK in the cathode follower role. A cathode follower never has a voltage gain of more than 1, so generally Vin = Vout. The Grounded-Cathode Amplifier Circuit A cathode follower is also known as a grounded plate amplifier, since the plate is kept at ground potential for RF. Can't see any reason why this one wouldn't work as well as any other new 12ax7 in those type of circuits. If needed, the purpose of a cathode-stopper resistor is to buffer a capacitive load from the (slightly inductive) output impedance of the cathode follower. . In such cathode follower circuits low-impedance loudspeakers have an advantage in that the voltage requirements from the driver are not so serious as is usually the case. The tail resistor and presence circuit resistance creates the relatively high voltage (around 32.5v DC) needed for the cathode follower function of the upper cathode. It is used to match a signal from a high impedance source to a low impedance load. A cathode follower never has a voltage gain of more than 1, so generally Vin = Vout. A 6J5, 6C5, 6P5G, or a 6SN7 would have worked great in this section, but I preferred to use a shoulder-type tube for aesthetic reasons. Click to enlarge. Some experimentation with circuit simulation with LTspice could reveal the characterstics of the circuit. The original name for this circuit is a Balanced Direct and Alternating Current Amplifier (Maurice Artzt, Radio Corporation of America, February 9, 1943, Patent 2310342). 6DJ8 / ECC88 SRPP Tube Preamplifier Schematic The cathode follower has a high input impedance and a low output impedance. Figure 3c. is in the cathode lead. Oct 6, 2016 - 12AU7 (ECC82) Cathode Follower Tube Preamplifier Schematic. The circuit universally consists of an ECC83 gain stage, DC coupled to an ECC83 cathode follower (usually in the same envelope), each with 100k load resistors. Series Connected Output Stages. It also supplies a near constant current flow shared between the two cathodes--as current increases through the upper cathode the current decreases through the lower and vice versa. Cathode followers are, generally, used as buffers - to isolate one stage from another, so their gain is less than unity. The input to the grid comes through a 100pF cap. In addition to its simplicity, direct coupling eliminates the . It is similar to the board shown above except the low voltage signals are routed through a ribbon cable to clean up the layout and fix a few pesky oscillations. It is also used for impedance matching. What it does offer is CURRENT gain, and is useful for driving current-hogging circuits like tone stacks. Figure 3a. The only potential trouble is that 100 volts on the cathode. This leads to several differences. THE CIRCUIT. Other Active Boards include a dual 12AU7 CCGC (Grounded Cathode/Follower) circuit with moderate gain and low output impedance. Although the load is in the cathode circuit rather than the anode, a load line can still be drawn in the usual way (see the basic triode gain stage ). It is also used for impedance matching. A cathode follower is usually fed by 200 to 300 volts on it's plate, and biased to put a given voltage at the cathode, and it acts as a unity gain buffer. It was measured that the output impedance of the source follower is fairly lower than the 1000 Ω of source resistor R2. The cathode follower amp is the PC board on the right. 250v is not going to hurt a 12AX7. I don't know what RF level the BC221AA provides. Notice the cathode follower feeding the 211? This design takes a different path a single gain stage using a low-mu triode with very low plate resistance (Photo 2). The FET can operate at a bias current of 20 to 100Ma (much more than a vacuum tube cathode follower) which insures a low driving impedance for the output tube. 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