switching primaries on OT: suitable DPDT switch

[Roe]

I have two amps with dual primaries on the output transformers. Could I switch primaries with a DPDT switch? The plate voltage is 425vdc and 460vdc on these amps. What kind of voltages should the swich be rated for? There shouldn't be more than a volt or two across the switch at idle. And I do not intend to switch while using the amp.

[pdf64]

Do you mean dual taps on the HT secondary winding, eg 350-320-0-320-350, and you want to switch between the 320 and 350V outputs?
If so, a regular 250V 1 - 2A quick make-break switch is fine, works great on my amps to tweak the power up or down a bit.

[Roe]

Do you mean dual taps on the HT secondary winding, eg 350-320-0-320-350, and you want to switch between the 320 and 350V outputs?
If so, a regular 250V 1 - 2A quick make-break switch is fine, works great on my amps to tweak the power up or down a bit.

Sorry I meant switching primaries of an output transformer (6k6 vs 8k).

[pdf64]

Oops, sorry
Regular 250V switches get used for triode - pentode mode switching and seem to survive fine even on 100W Marshalls, so I can't see why your application would be any worse than that.
https://drtube.com/schematics/marshall/2555amp.gif

[Stevem]

So you have two amps with duel primary's, but only one type of output
tube?
I am in my mid 60s now and I guess I have just crawled out from under a rock because I have never heard of a off the shelf OT with duel primary's.

So I guess your not talking about the primary's of a UL type OT here, or maybe OTs from a Mesa amp?

If these are off the shelf OTs could you post up the manufacturer of them if you know that info?

[luix]

Do you mean a switch like this?

final_switch.png

You should consider the voltage between the two taps and you should also consider that in PP amp, the off branch of the transformer see about the double of the power supply because it is driven by the on branch.

I think it's better to choose plastic type switch because referred to the ground (so to the chassis) the voltage on the switch pin can be as high as 800V, it is for short period but it can arch and cause audio noise.

[Stevem]

If as in the diagram above if that's what your taking about doing, then also as posted above with the combined voltage levels seen I would think that you would also need a way to kill the V+ to the OTs center tap before you make the switch to the other primary'.

Also all of the extra wiring involved would seem like a really good invite to a oscillation problem cropping up!

[luix]

If as in the diagram above if that's what your taking about doing, then also as posted above with the combined voltage levels seen I would think that you would also need a way to kill the V+ to the OTs center tap before you make the switch to the other primary'.

Also all of the extra wiring involved would seem like a really good invite to a oscillation problem cropping up!

Yes, I think that this is not a command I would put on the front panel, maybe on the top of the chassis with shortest cables possible, well protected and to be activated only after the power is off.

[pdf64]

...If these are off the shelf OTs could you post up the manufacturer of them if you know that info?

They're usually intended for JTM45 eg https://www.tube-town.net/ttstore/tube- ... jtm45.html

...You should consider the voltage between the two taps and you should also consider that in PP amp, the off branch of the transformer see about the double of the power supply because it is driven by the on branch.

I think it's better to choose plastic type switch because referred to the ground (so to the chassis) the voltage on the switch pin can be as high as 800V, it is for short period but it can arch and cause audio noise.

An overdriven tube amp into an inductive load reflects >2kV back to its primary.
Not that the votlage between the switch poles will be double that, so way higher stress on the insulation there than between either pole and the chassis.

I agree that the concept seems crazy, but as I noted, it works fine for Marshall triode / pentode switches.

[Roe]

So you have two amps with duel primary's, but only one type of output
tube?
I am in my mid 60s now and I guess I have just crawled out from under a rock because I have never heard of a off the shelf OT with duel primary's.

So I guess your not talking about the primary's of a UL type OT here, or maybe OTs from a Mesa amp?

If these are off the shelf OTs could you post up the manufacturer of them if you know that info?

yes, I'm thinking of the radiospares deluxe OTs or wreck express OTs with 5k2 and 6k6 primary windings

[Roe]

Do you mean a switch like this?
final_switch.png

You should consider the voltage between the two taps and you should also consider that in PP amp, the off branch of the transformer see about the double of the power supply because it is driven by the on branch.

I think it's better to choose plastic type switch because referred to the ground (so to the chassis) the voltage on the switch pin can be as high as 800V, it is for short period but it can arch and cause audio noise.

yes, something like that. Agreed on the plastic switch.