[Collins] 75S-1 Problem (update)

[GBabin73 at aol.com]

Well,
I re-aligned it with the swamping network and checked the IF gain with  a 
known/calibrated 50 micro volt source. This time I know for sure that the  
S-Meter reads 25 db over S-9 (65 db) at 50 micro volts with the IF gain set pot  
adjusted as low as it will go. There appears to be no ALC action at 1  micro volt 
and no distortion of strong signals (excluding my neighbor across  street). 
Nothing really stood out with voltage and resistance checks. I guess  I'll have 
to make  more through voltage/resistance checks and try tube  swaps. While I 
was trying to find the source of my outlandish S-Meter readings,  a couple of 
other problems cropped up. When the  calibrator is oscillating or I put the TX 
in synch mode, the  audio starts to crackle (maybe a noisy tube?). The second 
problem is  the PTO. Every so often, it suddenly jumps, at random, 1.5 to 2 
kc's up or  down. Otherwise it is rock stable. I replaced the 1N34A USB/LSB 
shift diode,  hoping that might be the problem. No joy. Next step is to scrounge 
some 1% or 2%  silver mica's, some good quality .02 bypass caps and shotgun 
the PTO (I'm  getting tired of pulling it out). I suspect it might be the 200 pf 
"postage  stamp" mica, most likely suspect, I have seen plenty of them go bad.
 
Thanks for reading my long winded dissertation and 73! DE N5MCJ,  Jerry 
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Thanks to all that replied!
Tried it terminated into 50 ohms, no change. I had to drop the signal to 10  
micro volts to get S-9. URM-25 might be way out of calibration, I'll try it 
with  the HP 606B. Even though, RX is still way too hot. Just  about every 
signal pins the meter. Maybe it's over coupled. I did not use  the "swamping 
network" (1K res. and .01 cap.) when I aligned it. All tubes  are correct, no mods, 
all paper and electrolytic caps had been replaced a few  years back. I tested 
all the tubes (mostly looking for  gas/shorts/leakage) and found a couple that 
had some heater to  cathode/plate leakage, replaced them and the signal 
levels went even higher.  Bias seems to be working OK (I can cut RF gain via the 
front panel  control, re-zero the meter pot and make signal levels more or less 
normal).  I'll give it another shot with a better sig gen and use the swamping 
 network.
 
Thanks again for all the info and 73! DE N5MCJ,  Jerry