PT trick: using a 110V transformer on a 220V outlet. Does it work?

[Baguette]

Hello,

I have an old Silvertone 1457 Amp in Case I'd like to use on the euro 220V wall outlet.

I'm thinking a bout a trick, and wondering if it would work.

Original PT has 110V primary and 320-0-320VAC and 3.15-0-3.15VAC.

Could I just plug this PT on the 220V outlet and use only the 320-0 winding for the HV and the 3.15-0 for the filaments?

Plugged on the 220, the filaments would be the correct 6.3V but the HV would yield 640VAC. Is it correct?
Then would there be a trick to rectify the 0-640VAC to yield the wanted 400 or so VDC?

Thanks!

[stratele52]

You'll burn the PT ,

Plug a 120V transformer primary in 220 V wall outlet will destroy Power Transformer primary .

[eleventeen]

I'd not recommended it. While the transformer would *probably* be OK at first, under time and heat...it probably won't after not much time. Keep in mind your full HV secondary, whether you use (all of) it in an amp build, is now in the 1300 volt range. That's asking for trouble, IMO.

[stratele52]

I'd not recommended it. While the transformer would *probably* be OK at first, 

For how many seconds ????

[PRR]

Iron is good magnetic support only up to a point. In both winding-voltage and time.

It's related to audio transformer bass power capacity. A 2*6V6 14 Watt OT can support 334Vrms at whatever its bass limit is. Would you apply 56 Watts or 668Vrms? If you try, you expect really crappy bass sound. The transformer overload is shorting-out the tubes. The tubes may not cook the transformer, but a power line can.

A "120V 60Hz" winding should stand 130V for a long time, but at 150V the iron has quit working and the loss of inductance allows uncontrolled current flow and heat. 230V is way-way over the top.

Moreover a 60Hz design fed 50Hz is 5/6th down on its margin, so some 230V 60Hz PTs over-heat on sustained 230V 50Hz.

[eleventeen]

"Moreover a 60Hz design fed 50Hz is 5/6th down on its margin...." [PRR]

That, too, is a big deal.

[Baguette]

Thanks for the replies folks.
I thought it was all about turn ratios. Like plugging a 110V PT into a 220V wall outlet would just double the end voltage at the secondaries, and not cooking it.
I'll just get a proper PT.

[stratele52]

Thanks for the replies folks.
 ........ and not cooking it.
I'll just get a proper PT.

It will cooking it for sure 

If you are sure of what you say ( only voltage at secondary change ) , disconnect secondary , to protect your amp and plug it in 220 wall outlet ...

[PRR]

Read Rod's transformer pages.

http://sound.westhost.com/xfmr2.htm

Jump to Figure 12.1.

This is a large and fairly bold "240V" transformer. With no load it should pull "no" current". 100-150mA is small-enough idle current for his purpose. But it is ~~30VA, and some part of that appears as heat. Push just a bit more to 260V and the idle current is 200mA and rising fast. By 320V it will be sucking at least 1 Amp no-load. The parasitic heat will be more than the full-load heat under design load. It will run very hot.

320V on a "240V" design is like 160V on a "120V" design. Yes, I would expect a 120V transformer fed 160V to run too hot to stand.

Yes, get a 240V:120V step-down.

Also consider a fan. The Silva-Tone is surely designed 60Hz only. 50Hz will also increase its stress. And IIRC correctly that chassis is crowded.

[stratele52]

 

Yes, get a 240V:120V step-down.

 

+1

[tubeswell]

60Hz@110VAC (red) vs 50Hz@230VAC (blue)



The area under the function curve in each case is the amount of power. 50Hz@230VAC is a lot more power, which the PT has to be designed to handle (bigger core etc to handle the larger amount of magnetising current).