You possibly could use a transformer out of an old battery charger. These
usually were half wave power supplies with no filter cap and 6 and 12 v
switch over here anyway. (center tapped)
You could then use a heavy wattage adjustable resistor or rheostat instead
of a Variac to adjust the voltage to a fixed value. While it is available
to be adjusted time to time, it won't accidentally be adjusted.
When I was a kid building 813 amps. I also used a pair of old rectifier
filament transformers in series in a pinch. (Those being 5VCT) a pair gave
me 10 V. When placed in series you had a new center tap. The units were
easily 10 amps each, done.
There's also the custom transformer shop like Pete Dahl etc..
I rewound a power supply transformer out of a TV once in HS electronics as a
project. Went to the motor rewind store and bought enameled wire etc
fiberglas tape etc...
I made my first 5V 30 Amp 3-500 transformer. I got an A on the project. It
was perfectly 5V under load and didn't buzz. I just hated taking apart all
the laminates and sticking them all back together and shellacking everything
again. What a crumby project.
That transformer was used in several 3-500 renditions over the years finally
leaving my ownership. I really miss that transformer. HAHAHAHA
BOB DD
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Steve Thompson
Sent: Wednesday, January 24, 2007 6:27 AM
To: amps@contesting.com
Subject: Re: [Amps] 813 Filament Transformer
Steve Flood wrote:
> I am building a 2x 813 amp and am looking for a filament transformer. I
need some coaching on a couple options since I cannot seem to locate a
proper 10V 10A transformer.
>
> 1) Use a 13v @ 20A transformer with a Variac.
>
> 2) Rewind a microwave oven transformer secondary with 10 turns of #12
THHN.
Either should work fine - it's fairly uncritical. I used a pair of 4.5V
50VA transformers - 4.5V is a common stock voltage over here - which
also provides a convenient centre tap.
Don't forget to remove the shunts if you use a microwave transformer.
Steve
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