Dual Power Supplies?

[Chuck H]

Yup. You were posting while I was editing I think.

[Enzo]

Well then instead of switching jacks, how about TRS jacks. Wired just like the input jacks on effects pedals and how they complete the battery circuit. The ring terminal completes the cathode to ground whenever a TS plug is inserted.

[Chuck H]

What if you used switching output jacks to engage the cathodes when they're plugged into. More intuitive in use. If a speaker is plugged in then it's getting powered. If it's not then that channel is effectively off. No chance that you might fail to have the standby in the wrong position and run the OT into an open load. I know switching jacks aren't notable for durability but there ARE some good ones and I think it's a more reliable system than leaving it to the player to always be cognizant of the standby switch. Even if (or especially if) that player were the builder.

EDIT: Just thinking about it,.. If you use plain old stereo jacks then the "ring" contact would effectively be on the mono jack sleeve when plugged into. If you are using un isolated jacks this could be used as a connection point for the power tube cathodes. In my experience the regular jack contact springs are more reliable than any isolated switches and such a jack can be purchased in an "open" style Switchcraft product. That should be sufficiently reliable I think. It also has the benefit of any likely jack failure rendering the channel off rather than any possibility of operating into an open load. In fact I may start doing this with my regular single output builds as a safety measure against open loads.

[Justin Thomas]

<IF> I don't hafta worry abput having a speaker load attached, I'd consider alternative methods to silence either of the two sides...

But like I said, it's pretty roomy so a couple extra switches won't bother me!

Jusrin

[g1]

Sorry, I think I'm mistaken. The Marshall 9000 series are true dual mono amps with separate PT's for each side.

The one I was thinking of was the Hughes & Kettner VS250, 4x6BQ5 per side, single PT. But it's standby switches lift the power tube cathodes for each side.
Schematics here: https://music-electronics-forum.com/...ad.php?t=50681

[Justin Thomas]

Oooh, thanks for all that, guys!

Justin

[nosaj]

I'm pretty sure one of the Marshall rack mount stereo power amps used the dual standby arrangement as you have outlined it.
All heaters always running.

Marshall series 9000 I think.
https://drtube.com/library/schematic...-schemas#M9000
nosaj

[g1]

I'm pretty sure one of the Marshall rack mount stereo power amps used the dual standby arrangement as you have outlined it.
All heaters always running.

[nosaj]

A DPST switch then?

Yeah, maybe I'll just leave the heaters be... I'm not likely to use one side or the other for more than 2 hours at a rime without a break. Definitely not gonna be using valuable tubes, except maybe an EF86 or two I have. Seimens, Mullard, a JJ. And a UOS 5U4GB.

Justin

No you need a big ole Dr Frankenstein Knife Switch mounted on top for effect at the church services you play. With some ole Doc Brown hair

nosaj

[Justin Thomas]

A DPST switch then?

Yeah, maybe I'll just leave the heaters be... I'm not likely to use one side or the other for more than 2 hours at a rime without a break. Definitely not gonna be using valuable tubes, except maybe an EF86 or two I have. Seimens, Mullard, a JJ. And a UOS 5U4GB.

Justin

[Leo_Gnardo]

For the heaters, I'll have the CT winding grounded. Would a simple SPST switch in half the winding be cool to cut the heaters? I'm not great with all that current theory stuff...

Your proposal would definitely reduce filament current to the inactive tubes to vanishingly small. BUT - I'm worried it would induce hum into your circuit instead of having the hum cut to nearly nil as it is with current draw equal on both sides of the virtual center tap. Only one way to find out... if it does induce hum then just let the filaments light up & don't sweat cathode poisoning. If you were were using some big bucks NOS or exotic output tubes, it's worth a worry. Also if you were planning to run the amp thousands of hours in mono mode. JJ EL84 or 6V6? Cheap and expendable.

[Justin Thomas]

It's my thread &amp; I'll derail it if I want to...

Here's the BM100 OT beside the PT with a JJ 6L6GC for comparison:

[Justin Thomas]

Thanks Leo,

I was thinking about the B+ rise... This thing might end upgetting a pair of 6V6s in one or both sides to compensate for that... It originally had 6973s in it. So the. 6V6s would be less heater draw anyway. I'm just trying to use junk I have on hand, one of which is a matched quad of JJ EL84s to blow...

For the heaters, I'll have the CT winding grounded. Would a simple SPST switch in half the winding be cool to cut the heaters? I'm not great with all that current theory stuff...

Jusrin

[nosaj]

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

Jusrin

I bet you've never dropped one on your foot then

Heavy enough I think the PT an OT from the evil twin are probably the biggest ones I have sitting around.
nosaj

[nosaj]

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.

Are you looking at some type of Stereo Tremelo or something similar?

nosaj