Yeah, based on the numerous examples you cite, Jim, and the LTspice
simulations, I am convinced that paralleling can work, but that there
will always be at least some current imbalance. Whether or not that
imbalance is significant depends on the specific parameters of the
transformers involved (e.g. secondary voltage matching, winding
resistance, etc) and how much imbalance can be tolerated.
Good discussion thread.
73, Mike W4EF...........
On 10/28/2025 11:36 AM, jim.thom jim.thom@telus.net wrote:
Date: Mon, 27 Oct 2025 17:53:01 -0700
From: Michael Tope <W4EF@dellroy.com>
To: amps@contesting.com
Subject: Re: [Amps] Paralleling plate xfmrs.
Hi Jim,
Do you know the primary winding resistance of the subject transformers?
73, Mike W4EF................
No clue. I don't think Scott has a lab supply with enough current to do
the job.
Right now, the primary's are wired in parallel, using the 250 vac taps for
initial testing.
On a similar note, I got email from folks who used to work for companies
that wound xfmrs. They all pointed out that TURNS counters are used to
count both primary...and sec turns....so each transformer ends up
identical.
One other thing, 7.5 vac @ 50 amp fil xfmrs (for a 3x3 tube) have been
paralleled to make a 7.5 vac @ 100 amp fil xfmr.....used for a 3x10 tube.
Zero issues there. Henry Radio did just that on their 3x10 amps. It's
common practise on hb 3x10 amps. The bigger 3x15/20 tubes require a 6.3
vac @ 160 amp fil xfmr.
Jim VE7RF
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