custom power transformer for switchable B+

[gary]

I noticed a German company building Marshall style amps with several stages of switchable power reduction via a custom transformer. The name Brian Wallace is mentioned. What do you think would be the premium for having such a transformer built ?

Does anyone supply such a thing from stock?

I'm thinking it might be a simpler solution for scaling a large amp, in terms of components and heat-sinking at least.

Any thoughts, pro or con?

[Jana]

Here is the link for Brian's website: http://marstran.com/

[myfoot]

I have a transformer from Chris Merren that has 3 different taps for a Marshall JTM45/100 . I think it's 560 520 and 490 but don't quote me on that. He's at http:// www.merrenaudio.com

I've built am amp with one of Brian's transformers too that had dual taps. I think that one was 420 and 390. His 45/100 also comes with 3 taps.

[David Root]

Thanx for that link to Chris Merren's site. He really has it down, especially on Marshall iron. Never seen anything like that before.

[gary]

any thoughts on the low voltage scaling possibilities, like on the gladius amps? Any drawbacks apart from limited variability?

[ToneMerc]

The forum members over at MetroAmp had MCI to produce this one.

http://www.classictone.net/40-18069.pdf

[dcribbs1412]

myfoot

I have a transformer from Chris Merren that has 3 different taps for a Marshall JTM45/100 . I think it's 560 520 and 490 but don't quote me on that

how is the switching done? regular 3 or 4 way power switch?
Thanks

Darin

[myfoot]

You could use a switch I guess but I just pick one and solder to the appropriate taps.

[ToneMerc]

myfoot

I have a transformer from Chris Merren that has 3 different taps for a Marshall JTM45/100 . I think it's 560 520 and 490 but don't quote me on that

how is the switching done? regular 3 or 4 way power switch?
Thanks

Darin

I have one of the multi secondary 45/100 PT's. It's not designed for switching perse', just lugs to wire whatever voltage you want. However, you could wire a 3PDT switch to select two of the three.

TM

[Phil_S]

I think such a PT would have to tap the various HV on the secondary. Moneying around with the primary means heater voltage will be a problem. I don't like the idea of switching that much voltage on any ordinary switch. You'd need a very hefty one rated for the voltage and I think you'd only want to switch it while the amp is not under power.

[dcribbs1412]

Thanks TM
wondering about what Phil_S is saying
could a regular 3A/6A switch be used safely
or maybe just wire up the taps see what sounds best.

Darin

[ToneMerc]

I don't like the idea of switching that much voltage on any ordinary switch. You'd need a very hefty one rated for the voltage and I think you'd only want to switch it while the amp is not under power.

Yeap, my 710V MM supply ODS makes me nervous when I switch the standy as well.

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.

[Reeltarded]

Or you could just ignore the internet and variac the whole thing. It's cheap, portable, and it works with every amp.

Don't fear the reaper. Fear his brother, the over-talkative drunk from across the street... oh jees, death's brother is at the door again..

[Jana]

You also need to switch the bias voltage too.

[dcribbs1412]

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