[Amps] Variac Question

[Chuck Curran]

Hi Larry:
You have several alternatives that could work for you, so here is one more.  How about a boost/buck transformer wired into your HV transformer primary?

You would need approximately a 10 amp transformer (or greater) rated at at least 70 VAC to achieve a no load 3500 VDC output from your transformer.  That would be a bit hard to find, so get a control transformer with a 115 VAC output and drive it with a small auto transformer, resulting in fully adjustable output voltage on you HV supply.  I've used that approach since 2008 on one of my HV supplies, works great.
Good Luck,
Chuck. W9KR

Sent from my iPhone

> On 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.
> 
> My other possibility is a pair of 110V 5 amp variacs that I have that are ganged on a common shaft.  I'm thinking I could series wire the coils and apply 220 V.  The problem then is that they are only rated at 5 amps each, which is not enough for a full power amp.
> 
> Anyone got any ideas short of going out and buying another variac?
> 
> Larry W4LK
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