[Amps] Variac Question

[Alek Petkovic]

No you don't need a centre tapped primary.  Read it again and draw it on 
a piece of paper.

Alek
VK6APK

On 3/02/2015 8:13 AM, Larry wrote:
> 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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