6V6 Rocket

[RJ Guitars]

Something else I was wondering about, it seems that with this amp, even though I have 1K screen resistors and the choke between the plate and screen nodes, that the screen voltage is hardly lower than the plates on the 6V6's.
Is that common with 6V6 or is it just the way the Rocket power supply works?

Thanks, Tom

Good work Tom, these are really versatile amps and take a wide variety of tubes and mods with generally good results...

We've seen this weird voltage thing before and it turns out that everything is O.K. and in fact probably working quite well. There was a guy named Lowell Hunt that post with us occasionally and he saw this and we did a pretty extensive research project to sort it all out. This comes up every now and then with a cathode biased amp and it can kinda freak you out at first.

If I can find that old thread I'll post a link, it was good stuff.

rj

[Cliff Schecht]

Something else I was wondering about, it seems that with this amp, even though I have 1K screen resistors and the choke between the plate and screen nodes, that the screen voltage is hardly lower than the plates on the 6V6's.
Is that common with 6V6 or is it just the way the Rocket power supply works?

Thanks, Tom

If the screens aren't drawing much current then there won't be a significant voltage drop. It's not a big deal, just something to keep in mind. Higher screen voltages means you're going to get more gain out of the power stage as well. If it sounds good then leave it..

[paulster]

At idle it's actually possible to get your screens voltages higher than the plates depending on the DC resistance of the choke compared to the OT primary.

So long as your screens aren't over their power dissipation rating at idle this isn't a problem though, as the voltages will come into line once some current gets drawn under load.

[Structo]

Thanks guys, I didn't know if this was something unique to this amp or to cathode biased 6V6 tubes.
I think I had calculated the screen current before but now can't find my notes.

The choke is the Hammond 158L
Specifications
Rating: 15 Henries, 75 mA
Max. VDC: 400
Resistance: 411 ohms

[tweedeluxe]

Yeah that KT66 rocket amp has gigged weekly for at least a year now with original output tubes . . .no issues - still sounds great. Here is a clip:

http://ryanhuntband.com/clips.html

Just a choke and 220Ω stoppers. The screens draw negligible current at idle