Signal applied to... Cathode?

[radstringz]

Looking at this schematic of an 80's Peavey Heritage, I'm a bit perplexed about the power amp circuit.

It looks to me as if the signal is being applied to the Cathode of the output tubes, and only a bias voltage on the control grids.

I've not seen this before, and I've been wondering if anyone else has. I also notice that the screen voltage is provided by UL taps on PT. Uncommon on guitar amps, but not unheard of. Are these design elements related, and if so, how?

And finally, why design it like this? Are there significant advantages to whatever is going on here?

[sluckey]

Signal is applied "BETWEEN" grid and cathode. We mostly see it as signal hot to grid and cathode at signal ground. But it makes no difference if you put the signal hot on the cathode and hold the grid at signal ground.

I suspect the SS driver circuit may work better sending the signal to hot in this hybrid amp. Seems like the Peavey engineers like it.

[Ken Moon]

That is a grounded grid configuration, if I'm not mistaken.

They have a low input Z, but high gain, and can be designed with very high PSRR. Lots if info out there seems to point to their use in RF amps.

Peavey did some weird stuff with guitar amp designs!

[Ken Moon]

I think the SS driver is required because of the low input Z of the grounded grid configuration, to avoid loading the input signal down.

[ToneMerc]

Reminds me of the MusicMan power section.

TM

[matt h]

(deleted)

[rock_mumbles]

I think this is pretty much the same:

http://www.music-man.com/techinfo_old/o ... 75-130.pdf

[radstringz]

Thanks for the responses, guys. I learn something every time I visit this forum. It's all making sense now.

Matt h, I'm hoping you're making a colloquial reference to the design. I'll be careful before reading your posts

[matt h]

(deleted)

[tele_player]

Seems to me one motivation for this topology is that the entire solid state section runs at +15/-15v, (+16/-16v on the MusicMan) and can't provide enough voltage swing to directly drive the EL34 to full power.

-Robert