My Old SRPP Notes... - Triode Kingdon - Tube DIY Asylum

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My Old SRPP Notes...

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In Reply to: Re: Self-bias should work OK in your application posted by Iceman on February 26, 2004 at 18:46:49:

>Can you clarify how -8.5V self bais of bottom half to produce big swing of 150V peak when only arround gain of 10 is provided ???
The output swing can't be figured solely on the basis of standing grid voltage vs. gain if the cathode is unbypassed. When the input signal moves in a positive direction, the cathode moves with it. So, the negative differential between grid and cathode decreases less than the amplitude of the signal driving it. In other words, the input swing can exceed the resting grid/cathode voltage by a considerable, depending on the other circuit values.
I went back to my notes on this from a couple years ago and found the page with my 6SN7 work. The numbers were taken with the cathode bypassed, although I later decided to let it float for the improvement in distortion and response. One of the SRPPs I built was a 6SN7 fed by a 400V supply. The cathode resistors are both 2.2K. Again, the lower cathode resistor is bypassed. I show that a 1V P-P input signal yielded approximately 15.5V P-P at the output. Anyway, with a 100K load, maximum swing from the SRPP was nearly 225V P-P. That agrees reasonably well with the measured gain and the resting bias, which I measured at 7.25V.
This was all tested with a 100K load, but the circuit can drive a lower RL by reducing the cathode resistors. I have one hand-sketched schematic indicating that I tried the 6SL7 with a 688 ohm lower resistor (where the heck did that come from?) and 620 ohm upper. There's no bypass cap, but I wouldn't swear that's not just an oversight. Anyway, this configuration was powered by a 370V supply, and ouptut was clean until nearly 200V P-P. I guess I didn't measure distortion during this particular test, but there's a note that there was no visible change to the waveshape switching between 100K and 39K loads.
This info is part of a collection of notes that I accumulated on SRPP design over quite a few months of work. I hope it helps in your decision.

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Follow Ups Full Thread

Topic - Can SRPP work in fixed bias ?? - Iceman 17:37:24 02/24/04 (13)

Absolutely YES.... - Kuei Yang Wang 00:59:04 02/25/04 (1)

Re: Absolutely YES.... - Iceman 17:55:39 02/25/04 (0)

No - Triode Kingdon 18:27:35 02/24/04 (10)

Re: No - Iceman 18:15:44 02/25/04 (9)

Self-bias should work OK in your application - Triode Kingdon 07:32:51 02/26/04 (4)

Re: Self-bias should work OK in your application - Iceman 18:46:49 02/26/04 (3)

My Old SRPP Notes... - Triode Kingdon 16:33:11 02/27/04 (2)

Re: My Old SRPP Notes... - Iceman 20:55:41 02/28/04 (1)

Here's the schematic... - Triode Kingdon 21:47:35 02/28/04 (0)

Re: No - Damir 01:26:37 02/26/04 (2)

Re: No - Iceman 18:18:25 02/26/04 (1)

Yes - Damir 04:55:24 02/27/04 (0)

I suggest... - Allen Wright 00:54:59 02/26/04 (0)

Follow Ups

My Old SRPP Notes... - Triode Kingdon 16:33:11 02/27/04 (2)

Re: My Old SRPP Notes... - Iceman 20:55:41 02/28/04 (1)

Here's the schematic... - Triode Kingdon 21:47:35 02/28/04 (0)

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