[TenTec] Corsair II Audio

[WA3FIY]

Last week I was getting ready to do some work on my Corsair II to 
minimize the AGC 'POP' [ more on that later ] but I also have been 
noticing lately that the audio did not seem to be up to it's normally 
nice crisp, clean, quiet self.   So.............decided to take a look at that 
matter first.

To make a long story short, I found a dirty BP Filter pot and an off 
tuned resonate circuit in the front end.   Normally when you turn the 
BP Filter pot fully CCW, the narrow bandpass audio filter is removed 
from the audio chain.  In my case there must have been some 
significant resistance at that position, hence causing a peaked audio 
response at 750 hz or so.   A small squirt of DeOxit took care of that 
problem.   I also treated the notch pot which was noisy.   That made 
a pretty dramatic improvement but the C II still didn't sound quite 
right.

The second problem was a little harder to find.   I applied a 
broadband noise source to the antenna jack using a Palomar noise 
bridge.   I then looked at the audio on the high side of the volume 
control using HamAlyzer sound card spectrum analyzer.  I could see 
immediately that the passband was dropping almost 10 db from 
about 300 hz to 2.5 Khz.   Switching to the opposite sideband, the 
slope changed to a 10 db rise 300 to 2.5 Khz.    The BFO 
frequencies were properly set so I thought maybe a problem with the 
crystal filter(s).   Feeding the noise source directly to the 9 Mhz filter 
board yielded almost textbook perfect response!   Had to be the front 
end.  On a hunch I readjusted C25 and C31 between the post mixer 
amp and the noise blanker gate and PRESTO, nice flat response!

Now the old C II sounds like new.    So there is another thing to look 
for if your Corsair sounds a little peaked or flat.   :-)

BTW, those who know me personally are probably laughing a little 
right now as I talk of how the Corsair SOUNDS.   I'm very nearly 
deaf much of the time and can't hear worth anything.   So when I say 
something sounds good you have to consider the source.    :-)    
Seriously though, it takes a very good sounding radio for me to be 
able to hear articulation well enough to be functional.    The Pegasus 
here is one such radio..........and now, so is my trusty old Corsair.

-- 

73 de Lee  WA3FIY
wa3fiy at radioadv.com

"There never was a truly great man that was not at the same time 
truly virtuous."   - Benjamin Franklin