[Collins] 32S3 loading control

[stbradford]

Robert Jefferis wrote:
> Smith,
>
> Adjustment of C80 is problematic, and is not likely to yield acceptable
> results without compromising the load setting on the other segments that C80
> influences. The root of the problem is S5 and the taps on L15. While the
> exciter tuning is capable of tuning any frequency in the specified range of
> the 32S-3, the emission tuning and load lever are not, because of the
> limited L15 taps. This problem also shows up on 17M. On 17M you can
> sacrifice the 21.0 band and add a tap for 17M between 1 and 2 turns lower on
> L15. I have never been interested in 30M, but the schematic shows that the
> unused 3C segment of S5 may allow you to add a tap to L15, again between 1
> and 2 turns lower than the 14 MHz tap, and get good results. This mod will
> not be for the feint of heart. It is risky to S5, and you obviously have to
> remove the PA cage. If you pursue a "proper" fix, be sure to use the same
> size buss wire, and be sure to flatten the end soldered to the coil (L15)
> just as the factory did to avoid a melt-down of the joint. There is a lot of
> RF current at that point.
>
> Several outboard kluge fixes have been published. One of these may be OK.
>
> V/R
> Bob KF6BC
>
> -----Original Message-----
> From: collins-bounces at mailman.qth.net
> [mailto:collins-bounces at mailman.qth.net] On Behalf Of w9hak
> Sent: Wednesday, July 23, 2008 3:14 PM
> To: Gerald Johnson; CRA Reflector
> Subject: [Collins] 32S3 loading control
>
> My 32S3 loading control capacitor is fully meshed when loaded up on 30 
> meters. In looking at the schematic it seems that increasing the 
> capacity of C-80, 100-500 pf, would help move the loading capacitor from 
> the fully meshed position. I have been living with this issue for some 
> time. I have to reduce the drive to maintain proper plate current.
>
> C-80 isn't easy to reach and I suspect it was set at Collins during 
> construction. Haven't found any information on setting up the loading 
> assembly on this transmitter. Therefore I have been hesitant in tuning 
> these capacitors. Any insight in the area would be greatly appreciated.
>
> Smith Bradford
> W9HAK
>
>
>
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>   
Good morning Bob,

Your assessment of the situation is clear and to the point. L15 tap
point is the problem but as you point out it's a nasty place to work.
Just having the dial string around a hot solder gun give pause about the
proper fix. I have added your missive to my file on the S Line database.

Without disturbing the radio I have opted for the "Kluge fix" that was
sent to me by an old time Collins user. The top of C-80 is connected to
the spare jack on the rear apron of the transmitter. This is easily
removable for the purest, and has no effect on the remaining 20 meter
band positions.

I assembled another C-80 in an aluminum box with a 'RCA' pin plug
mounted to the side of the box. Trimmed to around 400 pf it put the
loading control at the 50 ohm indicated point. When operating of 30
meters I just plug in the additional C-80 into the spare jack.  I now
get a nice dip at resonance and 80 plus watts out on 30 meters.

Of interest is the fact that not all of the 32S3's have this trouble.
During the 60's Collins equipment including the S Line was used through
out Asia. I suspect Collins changed something to be able to work the 30
meter area for military use. Your theory on L-15 would be the subtle and
effective change to fix this anomaly.

Smith Bradford
W9HAK