custom power transformer for switchable B+

[Reeltarded]

No, it won't mess with it, but it will lower it.

Oh. Yes. It will mess with it.

[DarnWeight]

Ampmaker in the UK offer a 20W PT with asymmetric windings (0-190-275), allowing for three levels of switchable B+. Product page is here.

I have one that's waiting to go into a 5f2a/two-stroke that I might get started on one of these days. The transformer's actually designed and built for use in Ampmaker's Double Six kit amp...there's a link to it on the product page I highlighted above.

[Phil_S]

I'll see if I can find the type of switch that George M uses, IIRC correctly it was a very heavy one. The wiring would also have a resistor wired to one of the throws to compensate for the difference in bias voltage as well.

Thanks TM that info would be great

as far as the variac..would that mess with heater voltage ?
Darin

I think he was kidding. Of course the variac messes with the heater voltage.

The amp rating of the switch is not the problem. It is the voltage rating. You might see, for example, a typical cheap switch rated at 120V/5A and 240V/2A. Good switches often carry an adequate rating -- maybe 1000V. On the secondary side, Amps (current) are not the problem. The typical guitar amplifier only has a fraction of an Amp on the secondary.

I think you will need a $5 switch, not a $2 switch or a $20 switch. Something like that. Check the specs before you buy.

[azatplayer]

Heyboer charge 5 bucks for each extra tap

[dcribbs1412]

Thanks
so far no luck on 1000v switches
I'll keep looking around

Thanks
Darin

[myfoot]

The dual voltage one here is the one George used to sell:
http://www.valvestorm.com/Products/Switches

[dcribbs1412]

Thanks myfoot
I'll look around for it


Darin

[Phil_S]

Try Mouser. The on line catalog is hard to manage unfortunately. I'm not an engineer, so maybe I don't really know enough to say this. I looked at the Mouser paper catalog and it looks like 250VAC is the standard. I'm thinking it's Watts that actually run on the switch. If you get one rated for 10A @ 250V, that's good for 2500W. You will probably be OK with that, but, like I said, I don't know. I would not chance the high voltage on a cheesy switch. You don't want that switch to melt.

[ampdoc1]

......but forget changing the high voltage. I tried this out a few years back in my first TWE. It works perfectly, and it's easy to install.

At that time I put a large (25W) 2-3 ohm pot in series with the output tube heaters. That was clunky, but you could turn the amp down to less than 1w and it still sounded the same (until the power wasn't enough to move the speaker cone sufficiently). And why not? The signal is unchanged all the way through the amp,..including overdriving the output tubes. You're just regulating the amount of electrons the power tube heaters are boiling off to feed the plates.

I swear this works well. And I think these days the same thing could be easily done with a VVR.

a"doc1

[dcribbs1412]

I apologize for kinda hijacking this thread
I have the MC Universal PT
it has Secondary Windings: 680VCT, 644CVT, or 580VCT @ 210mA DC
I'm looking at a JTM45 style build with 4 6V6's and be able to swap in
2 EL34's, 6L6GC, KT66 using the different taps.
Not sure it will work or it's worth the trouble...but wanted to experiment a little.

Darin