From: "Gerry" 
Subject: RE: [drakelist] Home brew PS question for TR4.


Make that +650V on the high voltage side and it needs to supply up to
500ma maximum or 325W. That's a lot more power than your transformer can
supply. For high voltage I would suggest a 1:2 line step up transformer
capable of supplying up to 1A of current. When used in a voltage doubler
circuit it should provide somewhere near the voltage and current you
need under load. I see those transformers occasionally from various
sources. The 207V/200ma winding likewise doesn't have enough "poop". You
need 50 watts, in other words 250V{at}200ma. Your winding can only supply
41.4W. Again, you might be able to find another transformer to meet your
needs or go up on the current rating of the HV side and supply it from
that half of the doubler, as Drake does in their AC-4. The big problem
in my opinion will be finding a 12.6VAC at 5.5A transformer. Those (or
reasonably close substitute) used to be plentiful at one time but are
scarce now. In a pinch I have used a DC supply for the heaters. Most
modern DC supplies have current limiting and that may be a problem on
power up. If you can adjust the current limit to something over what the
tubes need, you may be able to get away with it. At worst you may have
to wait a lot longer for the tubes to warm up as the supply slowly comes
out of current limit. That may be a good thing at least for the tubes if
not for the supply since they won't be subject to a big slug of current
when the filaments are cold. Another benefit would be a significant
reduction in AC hum since the only AC in the rig will be at the PWR
switch. It used to be easy in the old days. Just find a junked TV
somewhere and rip out the transformer but alas, those have gone the way
of the dinosaurs. 

-----Original Message-----
From: owner-drakelist{at}www.zerobeat.net
[mailto:owner-drakelist{at}www.zerobeat.net] On Behalf Of JJ HO
Sent: Sunday, April 04, 2004 5:07 PM
To: drakelist{at}www.zerobeat.net
Subject: [drakelist] Home brew PS question for TR4.


Dear drake lovers,

I am in the process of building a simple PS for TR4.
Judging from the circuit of AC4, I need a transformer
that can supply HV (~ 750V) and MV (~250V) and
LV(~ -70V).

I got a transformer with the following 2nd AC terminals:

- 289V/200mA: this can supply around 750V with
voltage doubling rectifying scheme.

- 207V/200mA: this can make a 250V.

The transformer had a 120/230V selection.  I wondered
if I could use one of the 120V primary as a AC source
for providing this voltage.

Also, for a 110V operation, do I need to connect the
two primary coils  in parallel or I can leave one as is.

Thanks for you answers and helps.

73,

Jonathan


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