Peter, I don't remember all the details of transformer behavior
characteristics. But there are ways of increasing the output of
transformer windings by adding additional turns to its secondary from a
second transformer. However, if the additional turns voltage is out of
phase with the original transformer, the net effect will be a decrease
(buck) rather than the desired increase (boost) in the desired voltage.
I was on top of the concept when I made the original mod, but the
details are somewhat vague in my mind these days.
I believe the increased output (1.5 KW) was indeed obtained by running
the amp in AB1 or AB2, i.e SSB mode even when running CW. I believe
that it didn't exceed the screen voltage specs on the 4CX1000A, but it
was on the high end of the range altho I can't be sure. The details are
somewhat vague in my mind after this many years and I'm sure I gave
myself an ad hoc crash course in the relevant technology at the time.
73 es 55,
Joe
K2XX
dj7ww@t-online.de <mailto:dj7ww@t-online.de>
Wednesday, May 27, 2020 4:15 PM
I don´t understand the "boost" question on the screen voltage.
The 4CX1500B should be run at 225V screen voltage as AB1 RF linear.
The voltage for the 4CX1000A is higher already.
73
Peter
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Joe
Giacobello,
K2XX via Amps
Sent:
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
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Joe Giacobello, K2XX <mailto:k2xx@swva.net>
Wednesday, May 27, 2020 2:17 PM
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
gordon.pritchard@gmail.com <mailto:gordon.pritchard@gmail.com>
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
CW.
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
achieve?
Thanks in advance!
-Gord Pritchard (VA7GP)
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