Choke cathode follower driver

Cathode-follower-based output stages are rare—surprisingly rare. A conservative guess would be that Yet the cathode follower produces far less distortion and a much lower output impedance than the comparable grounded-cathode amplifier does when working into the same load. Furthermore, the cathode follower is not straddled with the Miller-effect capacitance that the grounded-cathode amplifier is burdened by. So, the big question is, Why isn't the cathode-follower configuration used more often?

Dang good question. Of course, the obvious answer is that by offering no voltage gain, the cathode-follower output stage requires too high an input drive signal. This got me thinking: well, why not use two power supplies, one Vdc for the output stage and a Vdc power supply for the input and driver stages?

In this configuration, the cathode-follower output stage could get the huge input voltage swings that it requires, without having to withstand V on its plate.

But wouldn't sourcing a power transformer with two high-voltage secondaries be a pain? Probably so, but says that we need two high-voltage secondaries. This power supply is identical to a bipolar power supply, with positive and negative rails, except for where the signal reference ground, in other words falls.

Sure it can. If the ground were placed at the very top of the power supply shown above, we would have a purely negative power supply with a Vdc and Vdc rails. Well, you can use a tube rectifier for the output tube and two solid-state rectifiers for the input and driver stages. Before going any further, pause and consider just how cool this power supply topology is.

The 60V rail could be used for powering a solid-state output stage; the V rail, the tube input and driver stage. The idea behind the single-ended power amplifier shown below is that the MOSFET is configured as a source follower and that the 2mH inductor replaces the resistor. Don't you mean 2-Henry inductor? Thus, an air-core inductor isn't the slam dunk easy option that it might seem at first, in spite of offering such benefits as no saturation and no core hysteresis. For example, a typical 2mH air-core inductor might present a DCR of 0.

In other words, a larger-valued air-core inductor will be needed, say 10mH, but then it must incur a larger DCR. Okay, let's get back to pure-tube circuits. With two power transformers, it's easy to get two voltage rails. Moreover we need the extra heater windings, as the output tube's heater should attach to a floating heater winding referenced to its cathode, as the cathode will swing hundreds of volt up and down from ground.

The purpose of the negative supply in an A2 driver is so that the follower can swing equally as far negative as it can swing positive when direct-coupled to the grid of the final tube.

Diogenio said:. Click to expand You get more swing, but that just means you can drive the grid harder! You still get complete degenerative feedback, as you still have a cathode follower. You can now sing well below 0V, and maximum voltage swing is greatly increased.

To obtain this larger max voltage swing, you must apply more voltage to the grid. This is still a cathode follower with degenerative feedback and it won't have more than unity gain. Last edited: pm. Yes to more swing, but no to more gain. JMFahey Member. JMFahey said:. You read and repeat the words, but do not understand the concept. Plus "inductive collapse" is a poor description. Analyze it better. I used a 6LW6 sweep tube because I know how much abuse they can take without issue. The screen grid rating is volts, I ran it all day at volts.

The plate dissipation rating is 40 watts, I had it at 80 watts for about 2 hours, and up to watts for brief testing. At 80 watts there is no hint of plate or screen grid glow. At watts the plate gets a dull red glow after about 2 minutes. Consider the requirements if you choose a different tube.

All 6LW6's are not created equal either, some are not capable of this abuse. You need to choose a tube or parallel combination that can take this for extended time periods, you also need to plan the chassis for some heat dissipation.

Am I going to build one of these? First, I need to find a bigger OPT. Then, I plan to do some further testing. See those empty sockets, I plan to fill them up! I haven't decided which tubes yet, or just how much power it will make.

I probably will settle for a reasonably powered SE cathode follower, but I plan to build an insanely powerful P-P cathode follower if all of my other circuitry works out.

The Schematic. Today I revisited the cathode follower test circuit. I could only get 9 watts out of that amp during testing even when I cranked the tube dissipation up to watts. That just isn't right. I suspected my grossly mismatched output transformer, which turned out to be the correct assumption.

I was seeing almost volts peak to peak across the primary, but only 9 watts out. With almost ohms of DCR, all my power was just heating up the transformer. I then place power resistors in place of the OPT and experiment with the value to find the optimum load for the amp. If everything is connected to bench power supplies, you can adjust the plate voltage, the tube current, and the load impedance until you get exactly what you want.

Then replace the resistor with the same value OPT. No load lines necessary! It is 2 Henries at 2 Amps, with a 6 ohm DC resistance. I tried several different loads, and found that a ohm load resulted in 30 watts output with the tube on the edge of redness.

That is more like it. I settled on ohms for the best balance of power, distortion, and tube life. I can get over 20 watts with conservative tube current, and 28 watts with the tube at 80 watts of dissipation. Without the limitations of the OPT you can measure the amplifier circuitry itself. The disadvantage is a relatively large choke. In the next part of this series, we'll also talk about what to. Each substage is provided. This was designed to include "choke sink" for cathode current, and choke in anode feed for driver tube.

Probably nobody has ever built an amp like this because they need to source good quality chokes. The THD and Rout is much lower.. Usually class A2 is The output of the diode pump is applied to the grid of the amplifier, and the plate of the amplifier is connected directly to the cathode follower grid.

Thus, the. Briefly the operation is as follows: Energy is stored in a choke coil connected in series with the plate of a type drive tube, owing to the current flowing in this tube. Andrea Ciuffoli and his Audio Design Guide webpage. His site contains a long list of designs using Lundahl transformers. The output of the diode pump is applied to the grid of the amplifier, and the plate of the amplifier is connected directly to the cathode follower grid.

Briefly the operation is as follows : Energy is stored in a choke coil connected in series with the plate of a type drive tube, owing to the current flowing in this tube. That means plate choke - cap - grid choke. You will find the. Later I tried the 27,37,56,76 cathode bias into a DC coupled cathode follower. Cathode follower is. Third version of the A amp 4P1L choke- loaded cathode follower drive. A new idea raised. It may be feasible that 4P1L can be used as a cathode follower driver to the A SE amp unlike an idea of A possessing inherent cons such as a minus voltage PSU needed, b too much head room for driving to the.

In the next part of this series, we'll also talk about what to do with the grid of the 6H30pi. Some small range of adjustment might be needed to ensure the gain stages are matched though. If the gain stage is coupled to cathode follower outputs, this enables the output valve grid resistors to be kept to a sensibly low value, and provides the best drive capability of any of the circuits.

This arrangement does use rather. Bottom line is that the cathode follower doesn't embiggen the voltage from the grid, but it does add the current through the tube to make the signal stronger.

Making the signal stronger often helps it cope with driving following stages. The cathode follower is often used in this 'buffer' configuration specifically to provide low. With what amounts to an additional voltage amplification stage and a zero-gain cathode follower circuit, the 5F6-A tone stack requires the equivalent of a complete 12AX7 dual triode for adequate drive voltage.

Such is the technological price of placing an incredibly rich tonal palette in the hands of the guitar player. Ed, as we talked out on the air earlier today, the trick is to get the voltage swing from the preceeding stage, and use a cathode follower to drive the grids of the next tube. Some prefer the resistor to ground at the cathode, I prefer the choke method. If you get online and find a copy of the Altec B amplifier schematic, you'll. The amplifier of claim 8 , wherein said driver comprises a plate choke to provide a high drive voltage required to drive said at least one vacuum tube configured as a cathode follower.

As each winding of the choke coil has the same number of turns, full pentode driver operation is permitted in conjunction with a cathode follower coupling circuit by utilizing the auxiliary wind ings on the cathode chokes to introduce voltages into the suppressor and screen grid leads of the cathode follower tubes, thereby to.

As each winding of the choke coil has the same number of turns, full pentode driver operation is permitted in conjunction with a cathode follower coupling circuit by utilizing the auxiliary windings on the cathode chokes to introduce voltages into the suppressor and screen grid leads of the cathode follower tubes, thereby to.

I have some questions about cathode follower design.. Anyway, I'd like to setup a twin triode either a 6SL7 or 6SN7 as a gain stage directly coupled to a cathode follower as seen driving the tone stacks of various Marshalls. AC coupled through cap from cathode to one side of center tapped choke I have also included here the choke in the filter.. I first used the 12AX7,but wanted to make this one with more vintage tubes.

Another disadvantage is the large power dissipated in the interstage circuits because of the high driving voltage reduired and the high circuit capacitances across these tank circuits.

Cathode Follower The first attempt was to use tubes in a cathode follower circuit to take advantage of the inherent degeneration. This is neat adaptation of the standard Williamson circuit with a push-pull feedback loop and a cathode follower driver circuit with a very low output impedance. The driver circuit has enough "punch" to drive tubes that need a wide voltage swing i.

A choke is a. Basic reference-shift modulator. Choice of values is discussed in the text. Final," CQ, Oct. The unique cathode-follower driver circuit which makes a practical. I am prepared to use a filter choke in the power supply.. What is relatively unique is the use of a pentode cathode follower. The purpose in having a pentode CF up.. Are CFSs Poor? But we should not stop at. The filter choke, if your amp has one, and output transformer are connected to the highest voltages in For all tubes except cathode follower stages and output tubes in guitar amps, this means that the grid of.

I still have the original Mod transformer and main plate filter choke if anybody needs them. What you. I could not get that piece running but it's supposed to be a cathode follower design that eliminates the iron in the driver altogether. In my recent build, I decided to drive the tone stack with a cathode follower. I'm noticing that it's behaving strangely. The tone stack itself is a The aim of this journal is to increase the vacuum tube circuit vocabulary of the readers.

The Cathode Follower. A Quick Overview. Right after the Grounded Cathode amplifier, the second most common tube circuit.