OT Here is a schematic for Harmony H303B tube amp.

[Fret Wire]

Richard, glad to hear it's up and running and sounding nice. Nice job on the schematic (especially the isolation transformer warning). Future 303 owners will be gratefull for a clear, correct schematic.

Good Job!

[RLBJR65]

Yeah I have a tube radio on my bench and use it all the time

I submitted that schematic to them a couple of forum moves ago. Now the link I pasted on it doesn't work anymore I guess they will have to hunt a bit if they want to read that wonderfull explaination from R.G.

[RLBJR65]

That schematic was a bit to busy for me so I redrew it and added some voltages and other info.
http://aronnelson.com/gallery/albums/Richard-Boop-RLBJR65/H303B.gif
Anything I missed or other things to check? I thought I measured the B and C voltage but can't find it I'll have to check again.

The tone control came from looking over a few other hot chassis designs and a bit of experimenting. It's okay, not great but does add some low end which the amp was seriously lacking.

So... anyone want to talk about these a little? I'm really intrigued by an amp that can basically be made from old radio parts.
Plus I've got a few sets of these tubes and probably a couple of suitable output transformers

I'm thinking you could use 2 120V to 12V transformers back to back for mains protection and to power the 12V filament.
Shouldn't be to tough to figure out how to get the other heater voltages, couple of resistor and the heaters in series.

The 50C5 power tube is not known as a great tube for guitar amps

What makes them bad?
Could you point out some things for me to look for on the data sheet? http://frank.yueksel.org/tubes/sheets/093/5/50C5.pdf 

Thanks,
Richard

[JonFrum]

What makes them bad?
Could you point out some things for me to look for on the data sheet? http://frank.yueksel.org/tubes/sheets/093/5/50C5.pdf 

Thanks,
Richard

I dunno. People have used the similar 50L6, assuming it was related to the 6L6 - the same way the 5V6GT and 6V6Gt are identical except for heater voltage - 5V vs 6.3V. It may be that the lower max. plate voltage involves different design elements inside the tube that take away from  guitar amp mojo. Then again, maybe people just haven't tried hard enough to make it work. The series heater requirement puts people off investing in them very much. I have a couple boxes of 5V6GT tubes I got for a song, and they're great tubes.

[RLBJR65]

Thats kind of what I was wondering.
Are they just odd and not many have tried to use them or are they known to really sound bad?
I know there is a big difference sound wise if you run high voltage tubes at lower voltages but what if you use all low voltage tubes for an amp? Do only the high voltage tubes sound good?

Fred Nachbaur has a couple interesting push pull amps based on these. The 4X4 introduction artical is very interesting.
http://www.dogstar.dantimax.dk/tubestuf/4x4index.htm
http://www.dogstar.dantimax.dk/tubestuf/dv8index.htm

Richard