Dual Power Supplies?

[Justin Thomas]

I am trying to stick with what I have on-hand for tubes & other pricey parts here. I'm not ruling out 7189s or the original 6973s at some point, but with EL84s & acouple 6V6s I can use tubes I have on hand.

Justin

[HaroldBrooks]

There's a sort of good idea. You would have a bit of a rise in B+ for the output tube pair left running. I'll leave it to you whether you make a more complicated compensation for that when the amp's running one channel only. I'd say don't sweat it, chances are pretty good the bias current won't go way out of whack, but it is bound to rise a chunk, when you go single channel.

I can see shutting off filament current to the "sleeping" output tubes too, if you're worried about cathode poisoning which may take place in tubes left filament on with no B+ if left that way for extended time.

I might be wrong here, but you could also use a tougher EL84M or I believe a 7189 if you were concerned about the voltage and current draw rising when one side was cut out. That's actually what I am doing with my stereo amp, as I just yank the one side tubes and play a single side sometimes. Hope that is not screwing things up further ! But I have been getting away with it so far, and my caps are overrated for any rise in B+ as a result of pulling the unused side's tubes.

A swtich like Justin is looking at would be better, particularly with as Leo Suggested killing the filament connections as well. I like the idea Justin has overall, and may incorporate it myself instead of doing it the primitive way.

EL84M or 7189 are supposed to handle 400v on the plates, and 13.5 watts or so plate dissipation. They are the same pin outs. I saw something about an IC connection, but this didn't effect anything in my amp at least.

[Chuck H]

That's how the Hughes & Kettner I referred to in post #21 does it. There's a schematic link there.

I was late getting to this thread so I "skimmed" (though that's bitten me more than once). But yeah. That's the idea. The TRS jacks would act as an 'auto cathode lift standby'.

[g1]

So lemme get this straight. If the cathodes are ungrounded, I can leave all the other stuff (voltages - plate, screen, heater, bias) running, AND not blow up my OT if I don't have a speaker plugged in?

(No details right now, just "doofus-level concept) but, am I hearing this concept right?

Justin

That's how the Hughes & Kettner I referred to in post #21 does it. There's a schematic link there.

[Chuck H]

Hooray! Okay, that sounds a LOT easier & cheaper! I'll give it a shot.

Good thing I make my own front playes, covering up all those rendered-unnecessary holes I drilled last night!

Justin

Yupper. I've covered up "design change" holes many times. I'm going to do that with the project on my bench now in fact. There are plenty of examples by respected manufacturers that do it too either because they change a model and still have a bunch of the old chassis or because they use the same chassis for more than one model.

Now you can have a single standby switch. Or no standby switch. Many posters here have determined there's no real advantage to them for guitar amps. Well, other than actually using them to put the amp on standby so the filaments remain hot rather than turning the amp off. But as for the standby switch making for a gentle startup or shut down there are several threads here where it's been pegged as a misnomer.

[Justin Thomas]

Hooray! Okay, that sounds a LOT easier & cheaper! I'll give it a shot.

Good thing I make my own front playes, covering up all those rendered-unnecessary holes I drilled last night!

Justin

[Chuck H]

....and no tube current means no OT current.

Right. After all, we test amps for "unloaded" conditions with no tubes in them all the time. No OT's are blowing up because of it.

[Helmholtz]

....and no tube current means no OT current.

[Chuck H]

Nope, didn't sleep well.

Clear on the jacks. So if I use those, my OTs & tubers won't blow up? Even with all the other voltages appied?

Justin

Nope. They won't blow up. And they won't conduct and make noise. They'll just sit there with voltage on them not doing anything. No cathode connection = no current. No current = no potential for damage.

[Justin Thomas]

Nope, didn't sleep well.

Clear on the jacks. So if I use those, my OTs & tubers won't blow up? Even with all the other voltages appied?

Justin

[Chuck H]

Yes. Non shorting plain ol' Switchcraft "stereo" jacks. And lifting the cathodes from ground is pretty common. Used as a method of standby and also as a half power circuit where the cathodes of two out of four power tubes is lifted.

I hope you're still sleeping I didn't sleep well.

[Justin Thomas]

And, I think TRS (STEREO) jacks come in shorting & non-shorting versions. I think. I'll look again. Do I want the NON-shorting Stereo Open-Frame Switchcrafties, right?

Justin

[Justin Thomas]

It's now 3:15a.m.!

So lemme get this straight. If the cathodes are ungrounded, I can leave all the other stuff (voltages - plate, screen, heater, bias) running, AND not blow up my OT if I don't have a speaker plugged in?

(No details right now, just "doofus-level concept) but, am I hearing this concept right?

Justin

[Chuck H]

For the record, I always use Switchcraft jacks & plugs unless I'm repairing an amp with a PCB. So I'll look into all of that. I just didn't think it was a great idea to leave a speaker jack shorted to safely kill output. I'll read over it when it's not 3:00a.m. That solution sounds cheaper, too...

Justin

No no! Not a shorting jack, a stereo jack. Or TRS jack as Enzo indicated. The jack wouldn't short the output when unplugged, it would only connect the power tube cathodes when a male jack is plugged in. That way when no male jack is plugged in the power tube cathodes for that channel are not grounded. Which is actually used as standby for some amp models.

[Justin Thomas]

For the record, I always use Switchcraft jacks & plugs unless I'm repairing an amp with a PCB. So I'll look into all of that. I just didn't think it was a great idea to leave a speaker jack shorted to safely kill output. I'll read over it when it's not 3:00a.m. That solution sounds cheaper, too...

Justin