[Milsurplus] More TCS

Thu, 20 Nov 2003 12:46:24 EST

Ray,

Upping the high B+ to 450-500 will work fine.  I have a complete TCS-14 that 
normally I operate from a PP-380/U.  Years ago (>15) I made one mod to the 
PP-380 by removing the spare fuse holder clips and installing the GK-9-32SL 
Remote connector (for some strange reason excused with some double-talk in the 
manual, the stock PP-380 doesn't let you use the Remote/Speaker unit) but there 
was a little 120 Hz ripple on the 230 and 400 V rails.  The filter 
configurations are both pi so I paralled the output capacitors with electrolytics.  The end 
result (besides much less ripple) was about 460 VDC instead of about 410 out 
of the nominal 400 V supply (CW key down).  It's been running that way ever 
since.

You can in fact keep both 1625 finals running in AM by tacking an easily 
removable jumper across the appropriate terminals on the Voice/CW switch.  
However, as others have mentioned, there isn't enough audio available to make it 
really worthwhile.  The modulator consists of only the carbon mic, mic to P-P 
grids transformer T101, the two 1625's and the modulation transformer T102.

Ratings on T102 given in NAVSHIPS 900,291 and several other TCS manuals are:

Primary 6000 ohm C.T. 1700 turns #33 enamel
Secondary 6000 ohm 1702 turns #33 enamel
20 watt 200-5000 cps

I assume the 20 watt means 20 watts of audio which would certainly modulate 
25 watts of RF.  But no-where have I been able to find what Collins rated the 
secondary current at.  You could back into it knowing the wire size except that 
you would also want to know the iron cross section, which would require 
cutting open one transformer.  I would bet that you wouldn't hurt the transformer 
running both finals but you would need to try to keep the source and load 
impedances close to the transformer ratings.  For example, if you upped the high B+ 
to 500 and loaded it to 125 MA, you'd still be at 6000 ohms.  I wouldn't go 
any higher than that (even though 1625's are rated for 600 in Class C phone) as 
there are a lot of other components to consider.  Also, don't forget that 
grid drive requirements are higher for Class C phone than for CW.  Etc.

I recall dimly that there was a set of modification instructions floating 
around some of the MARS circuits years ago that included a speech amplifier of 
some sort.  Recently, I and at least one other ham have come across transmitters 
that had probably had this or a similar mod made, but at least in the one I 
have, the workmanship was so bad that I didn't even try to figure it out.

In a message dated 11/20/2003 10:29:05 AM Central Standard Time, 
[email protected] writes: 
> I am not intending to modify or change the original design of the TCS 
> transmitter, will drop the idea of running the second PA tube, but because I do 
> not have the original AC power supply, I am building a external modern supply 
> and their are legitimate questions on what can safely be supplied as a plate 
> voltage with this radio, if by increasing the plate voltage by a hundred volts 
> or so  you have the benefit of a couple more watts how can that hurt? 
> although I do not think I can reach the goal of twenty five watts of AM phone if I 
> did that would be a doubling of power from the twelve watts or so the radio 
> normally produces, that's 3 Db, in retrospect would you decrease by half the 
> power of your transmitters and run them that way? after all its only 3 Db. One 
> of the aspects of my application of this hobby is to try to get the best 
> efficiency and performance from these designs. but this is all apart from  my 
> point. The real question is if their is any history of failure of the 
> modulation transformer in the TCS and if anyone has any experience in operating them 
> on higher plate voltage and how it will affect its existing components? The 
> idea of additional microphone drive external to the radio to develop higher 
> level of modulation and more peak envelop power sounds good, but brings me back 
> to the same question, what will the modulation transformer take before 
> breakdown?

73
Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
<[email protected]> (Primary email)
<[email protected]> (Backup email)

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