[Amps] Variac Question

[Larry]

Mike,
If I understand correctly, to do what you are suggesting, I would need 
for the primary to be center tapped.  This transformer is not center 
tapped, but does have some taps for setting the primary voltage - 205, 
220, 230, 240, 250.  It is an old Gates plate transformer from a 
broadcast transmitter.  I might try Chucks idea for using a bucking 
transformer.  I think I have one that would work.

Another possibility is to use the 250 volt tap on the primary and wire 
the secondary in a choke input configuration. I have the choke that was 
used with this plate transformer.  That might be enough to get the 
voltage down where I need it.  If not, then I could add a bucking 
transformer.  4000 volts is my absolute max.

I'm using a GS-35B which is marginal at that voltage, but I've seen guys 
running them that high with no problems.  If you fry a tube, they are 
relatively inexpensive. A friend who recently became a SK gave me four 
of them, so I should be good to go for a while.

Thanks for the tips, guys.

Larry W4LK





On 02/02/2015 03:58 PM, Mike Waters wrote:
> It sounds like a 115 volt-only Variac, so you can use it between the
> neutral and one 240V leg. You just connect your 240V plate transformer
> primary between the Variac wiper and the remaining leg of the 240V circuit.
>
> That's the way my filaments are wired in my dual 833C amplifier. You get
> finer control of the voltage, but you can only adjust the primary between
> 120 and 240 rather than 0 to 240.
>
> 73, Mike
> www.w0btu.com
>
> On Mon, Feb 2, 2015 at 2:41 PM, Larry <LKIRKLAND at sc.rr.com> wrote:
>
>> I am building an amp and have started gathering parts for it.  My plate
>> transformer secondary is rated at 3500 VAC.  Thats a little much for what I
>> need.  I need to end up with about 3500 VDC for the amp.  I found an old
>> General Radio Variac type V10 good for 10 amps, but I'm not clear if it can
>> be used on 220 VAC.  The wiring diagram on it says "volts shown for input
>> 115 volts 50-60 cps."
>>
>> My question is Can I put 220 volts across the coil without smoking it?
>> I'm thinking that it would work.
>>
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