Dual Power Supplies?

[Leo_Gnardo]

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.

[Justin Thomas]

They're not that heavy. Of allmy amps the Bassman 100 has the record - the OT is 2x the size of the PT.

Jusrin

[nosaj]

Nah, I don't THINK so! I've already got the PT from the original amp. If I hafta end up adding a filament tranny, I will.

And I've got a Fender Twin Reverb tranny sitting at home anyway.

Thanks, though!

Justin

You know if push ever comes to shove i think you can workout with the PT and the OT.
nosaj

[Justin Thomas]

You need the PT from an Evil twin I've been hanging on to, to run that?

nosaj

Nah, I don't THINK so! I've already got the PT from the original amp. If I hafta end up adding a filament tranny, I will.

And I've got a Fender Twin Reverb tranny sitting at home anyway.

Thanks, though!

Justin

[Justin Thomas]

Harold,

I was just wondering if having the dual Standby switches would be okay to just "shut down" one side of the amp if I don't have a stereo cab or two cabs. If I only run one side, I'd like to keep the other side "safe" without having to plug in a dummy loa or some other switching thing. I could add a heater switch for each side also if that would help keep the tubes alive longer.

The only thing that would be "on" all the time would be the negative bias supply for the EL84s.

So I was just asking whether the switching arrangement would work.

Justin

[nosaj]

Justin, this doesn't answer any questions directly, but I have recently come into possession of a very similar stereo Zenith amp (2 x EL84 per side, 12ax7s and 5U4GB). It uses a rather large common PT and I've made some changes so I could use it as a guitar amp. The chassis I have only contains one 12AX7 used as a second stage and a PI. The schematic lists the 12AX7 as a 6FQ7, and that was changed at one time or another. ] The amp sounds great by the way, and I am amazed that I missed out on EL84 tubes for all these years. I had some irrational bias towards skinny tubes, but no more !

The Zenith stereo output transformer configuration is an odd one, but I will leave it to you extract anything that might be helpful or [B]useful in some other way.[/B

[ATTACH=CONFIG]58002[/ATTACH]

Silvertone 1485 is another dual OT config

[nosaj]

Here's what I was thinking...

You need the PT from an Evil twin I've been hanging on to, to run that?

nosaj

[HaroldBrooks]

Here's what I was thinking...

Justin, this doesn't answer any questions directly, but I have recently come into possession of a very similar stereo Zenith amp (2 x EL84 per side, 12ax7s and 5U4GB). It uses a rather large common PT and I've made some changes so I could use it as a guitar amp. The chassis I have only contains one 12AX7 used as a second stage and a PI. The schematic lists the 12AX7 as a 6FQ7, and that was changed at one time or another.

The amp sounds great by the way, and I am amazed that I missed out on EL84 tubes for all these years. I had some irrational bias towards skinny tubes, but no more !

The Zenith stereo output transformer configuration is an odd one, but I will leave it to you extract anything that might be helpful or [B]useful in some other way.[/B

Oh, and there is another one RIGHT NOW for sale on ebay for what I consider inexpensive, (if you don't mind dealing with the odd output transformer arrangement). The PT alone should be worth the purchase IMHO : https://www.ebay.com/i/223704672737?...yABEgKpLvD_BwE

[Justin Thomas]

Here's what I was thinking...

[Justin Thomas]

Hi All,

Making an amp with 2 OTs from an old tone cabinet chassis. This is gonna be a head, so I may not brme able to run 2 cabs/separate speakers at all times.

Thinking to put 2 Standby switches, one each to cut the B+ to the CT of each OT. Would also have each respective following power supply node downstream of that amp's Standby switch. Basically, two separate & complete parallel supplies.

I'm trying to make it so I don't have to worry about dummy loads or always having a speaker attached to whichever amp I'm not using.

Alsothinking to include heater switching for each side? That way any side I'm not using can basically be totally shut off...

I have a roomy chassis & radial caps are tiny & cheap. Rectifier is a 5U4GB. I'll see if I can attach a pic from my phone; values can be determined later. This amp is also for me, as I need something a bit less powerful
2xEL84, 2x12AX7 per side.

Thanks,

Justin