Top Boost Single Ended

[leadfootdriver]

you could parallel the first stage. if you change ra to ~100k, rk to ~820, both rg's to ~33k i doubt you'd lose any sparkle. i'm pretty sure you would drive the second stage more efficiently too.

I tried that with but didn't like it. However, I just found an AC15 handwired schematic where they keep the stock 220k/1.5k-22uf deal but parallel the tube! It works pretty good from what I can tell. What's the gain factor for that?

http://www.blueguitar.org/new/schem/..._handwired.pdf

[Diablo]

I tried that with but didn't like it. However, I just found an AC15 handwired schematic where they keep the stock 220k/1.5k-22uf deal but parallel the tube! It works pretty good from what I can tell. What's the gain factor for that?

http://www.blueguitar.org/new/schem/..._handwired.pdf

Matchless DC30 does the same thing with the parallel 12AX7 triodes. The only difference is they add another cathode bypass cap (.1mfd) in parallel with the 1.5K resistor and 22 mfd cap. I don't understand what mojo is added by the .1 mfd cap.

[loudthud]

Is that a 1.5K on the second gain stage cathode? Try lowering it to 1K or 820.

[leadfootdriver]

Is that a 1.5K on the second gain stage cathode? Try lowering it to 1K or 820.

I seen the in Trainwreck pages that smaller Cathode resistors yeild more gain right before I read this! I'll try it.

I was going through the Vox website and found a 1978 version where they do use another gain stage right after the reverb driver and before the PI. They also use a huge 3.3M grid resister! I circled them in red.

[R.G.]

I seen the in Trainwreck pages that smaller Cathode resistors yeild more gain right before I read this! I'll try it.

The gain approaches the plate resistor divided by the cathode resistor, so lower cathode resistor without changing plate resistor gives more gain, as long as the low transconductance of the tube can keep up.

They also use a huge 3.3M grid resister! I circled them in red.

I believe that's to isolate the reverb send from the reverb return to keep the reverb electronics from oscillating.

[leadfootdriver]

The gain approaches the plate resistor divided by the cathode resistor, so lower cathode resistor without changing plate resistor gives more gain, as long as the low transconductance of the tube can keep up.


I believe that's to isolate the reverb send from the reverb return to keep the reverb electronics from oscillating.

THanks for pointing that out. And man, that amp has a lot of tubes.

I added the 3rd stage with a 47k/3.9k cathode. The schem called for a 4.7k but I didn't have one. Maybe I'll get some latter and try it, but so far this by far the best it's sounded I think. It's real dynamic and has more sustain.