-----Original Message-----
From: Jim Thomson <jim.thom@telus.net>
To: amps <amps@contesting.com>
Sent: Fri, Nov 1, 2013 5:28 am
Subject: [Amps] Large Variac controlling HV power supply
Date: Thu, 31 Oct 2013 09:53:11 -0400
From: "David Jordan" <wa3gin@comcast.net>
To: <g8on@fsmail.net>, "Mark Beckwith" <r-emails@n5ot.com>,
<amps@contesting.com>
Subject: Re: [Amps] Large Variac controlling HV power supply
### He said he has a 5000 V @ 3A CCS plate xfmr. 5000 x 1.414 = 7070 vdc
NO load...with a FWB + high C filter. Your shunt relay to bypass the variac
is
just another method to step start the B+ supply. The supply will still be
running
at max full voltage. That’s fine..IF he wants a 7070 Vdc no load B+ supply.
## If he wants say a 4000 vdc supply, your scheme wont do him any good, in
which case,
the variac must remain in the circuit at all times.... and simply dialed up to
whatever
vdc he wants.
Gentlemen:
I have a problem that has perplexed me for several years. I got my Extra
ticket in
1970 and worked for 30 years as an Electronics Engineer.
I first built a 3-1000Z HF amp and then a 8875 HF amp both using a 4000
volt - 1 amp
power supply. My HV transformer was a Peter Dahl 3000 VAC (4.5 KVA),
FWB with 32 uF oil filled capacitor. I had a relay actuated step-start system
with
mercury plunger. The 220 VAC transformer primary was directly connected to the
output of a 220 VAC variac. The variac was no more than 10" diameter x 6"
width and
probably was not rated at more than 10 amps AC. This variac operated
admirably varying the DC supply voltage from 0 to 4000 volts under load ....
the input
220 AC voltage and the 4000 V DC output voltage were both metered. Talking
with friends, ( I no longer have the power supply) I have not been able to
figure how
this arrangement (10A variac worked for two years). I remember once that the
220 VAC
input circuit breaker actuated when an overload condition existed.
Can anyone suggest how this conundrum may have occurred?
Thanks & 73 de Dave, WT8R
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