[Amps] 30S-1 screen-boost question

Wed May 27 18:39:21 EDT 2020

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 at t-online.de <mailto:dj7ww at 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 at 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 at 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 at gmail.com <mailto:gordon.pritchard at 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)
>
>