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Re: [Amps] 30S-1 screen-boost question

Subject: Re: [Amps] 30S-1 screen-boost question
From: "Joe Giacobello, K2XX via Amps" <>
Date: Wed, 27 May 2020 14:17:37 -0400
List-post: <>
Gord, you're really testing my alleged memory.  I did, in fact, make this mod, but I sold my 30S-1 with the mod intact about 15 years ago.  It's very easy to do and there should be plenty of references to it on the web and among the Collins aficionados.

I believe the mod involved connecting a 1:1 (115VAC in to 115 VAC out) isolation transformer across the primary and secondary windings of the main power transformer that were used to provide the screen voltage to the corresponding rectifiers and filters.  These added windings have to be done in such a manner that the added windings "boost" and don't "buck."  One also had to replace the screen supply filter capacitor to accommodate the increased voltage.  I used the original 4CX-1000A and was able to get 1.5 KW out, although the power transfomer routinely groaned a lot.

That's my recollection of the process, but it's all very vague in my mind, and I would verify all the details.

I'm surprised that there are no Collins forums on the web that you can consult.  Accordingly, I've copied the Amps mailing list on this reply, and I'll wager that someone there can unhesitatingly provide you with expert information.

73, Joe
K2XX <>
Tuesday, May 26, 2020 6:16 PM
Hi, gentlemen:

I Googled and found some email-archives from a decade
ago, where you both were emailing about 30S-1 screen boost mods.
I hope you're both (still) doing well...

I overhauled a new-to-me 30S-1 which was far-from-
working. I changed the tube to a 4CX1500B, and I added a boost-
transformer. But I'm not really happy with how it works, so I'd
like to ask what you did, how you connected this screen-boost,
and how it works for you?

I opted to use a 100VA transformer, with 120/240 dual
primary windings, and a 120V secondary winding. I connected the
dual-primaries exactly to the main transformer T201 on the 'SSB'
connections. The idea was:

-I wouldn't get any screen-boost until after warm-up and then
only when HV enabled.

-by using the SSB primary-winding taps on T201, I anticipated
that my boost would be ~120VDC on SSB, then reduced to ~65VDC for

During no-load DC start-up testing, my anticipated CW
boost was only ~40VDC; lower than expected. I did not worry
about this.

During full-load operation now, I see significant sag to
my boost :-( With a common 500mA plate-meter reading for both
CW, and single-tone SSB (the only changes are plate-voltage and
bias-voltage), my total screen (T201 + boost):

SSB total screen = 320VDC, down from idle-only (250mA) 370VDC
CW total screen = 220VDC, down from no-load/no-Ip 271VDC

My questions for both of you:

Where did you wire-in your boost-transformers? Is it the
same - and how much is it - between SSB and CW?

What sort of Power In / Power Out are you able to

Thanks in advance!
-Gord Pritchard (VA7GP)

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