[Amps] 813 Filament Transformer

[Robert B. Bonner]

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 at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Steve Thompson
Sent: Wednesday, January 24, 2007 6:27 AM
To: amps at 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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