Switchable secondary voltages on power transformer?

[beasleybodyshop]

I just purchased the iron for my blackface princeton build. PT has dual secondary voltages. If I wanted to make this switchable, would I use a DPST switch? Would I have to adjust bias if I switched back and forth? Has someone already been down this path? If so please enlighten me!

[Cantplay]

In this schematic you can see the B+ is switchable.

I have a couple of his amp kits, and they're excellent btw.

http://www.ampmaker.com/images/ak02kit/ak02sc2.jpg

The 190V and 275V taps are obvious. The third setting of the switch is the difference between the 2, 85V.

As long as you bias at the highest voltage there should be no problems at lower.

John

[surfsup]

RJs Eagle Supre has switchable Edcor secondaries. Schematic is uploaded. Just do a search on the forum it will come up.

[ToneMerc]

Courtesy of George M @ Metro Amps

http://metroamp.com/wiki/index.php/Dual ... _switching


TM

[beasleybodyshop]

Courtesy of George M @ Metro Amps

http://metroamp.com/wiki/index.php/Dual ... _switching


TM

perfect!

Considering that my princeton transformer doesnt carry a bias tap, would the bias resistor on the switch be necessary?

[Structo]

And to state the obvious, only switch when the amp is off.

[beasleybodyshop]

And to state the obvious, only switch when the amp is off.

Thanks for the heads up.

[Structo]

What I mean to clarify, is that it probably wouldn't do more than a loud pop if switched
when powered up, but to ensure no damage, the best course of action would be to switch
it when it is not powered up.

[beasleybodyshop]

What I mean to clarify, is that it probably wouldn't do more than a loud pop if switched
when powered up, but to ensure no damage, the best course of action would be to switch
it when it is not powered up.

I see valvestorm carries that toggle switch. Is there an alternative on mouser? 275 or 315 seems like a lot of voltage to be running through your typical 120v carling switch...

[Structo]

Well, you see, most if not all switches are rated with AC voltage.

That is because with AC it reverses polarity every cycle.

With DC current the rating has to much higher because it has a tendency to arc because the current is steady.

So most Carling switches are OK to use for Standby (DC) but there is always the chance that the switch will be damaged by the direct current.

But, most power switches are built robust enough to be able to
survive many power cycles, despite the harmful DC switching.

On my amps I have always followed this method of operation.

I turn on the amp with the power switch and the standby to the off position.
After a couple minutes I turn the Standby to the play position.

Now here is where I differ from some guitarists, when I power down, I just flip the power switch off.

So in other words, I turn the AC supply off, while leaving the DC standby switch in the play position.

Therefore, I am only using the standby switch half of the time verses every power up and down cycle.

[martin manning]

That's the ticket, and you are draining the charge from the filters too.

[beasleybodyshop]

so I could just use a standard DPDT carling switch and call it a day? Thanks for the info on the switch rating.

[Structo]

I didn't mean to complicate the question.

Most toggle switches are rated at 250v around 10 Amps.

But that doesn't mean you can run a 10A machine with one of these switches.

What it does mean is that it is a heavy duty switch that will work
under most criteria.

The problem lies in the way a switch functions.
With DC current, the switch contacts can arc when switching on or off.

In other words, a heavy duty switch is going to last a long time before anything bad happens.

[Bill Moore]

My Music Man switches between the 2 taps, and has a center position for standby.

[ToneMerc]

I see valvestorm carries that toggle switch. Is there an alternative on mouser? 275 or 315 seems like a lot of voltage to be running through your typical 120v carling switch...

The first two high voltage Dumble like amps I built have 700+ across the standby switch, which has never given me the warm and fuzzies. The third one I put the switch on the cold leg to prevent this situation.

TM