[NJARC] AK 80 question - more tsuris

[William S Zukowski]

Tried Al's idea (grounding the cathode), and do I seem to get more gain 
(volume), thanks Al. 
However, there is slight audio distortion (this way and with the
original wiring).  Happens on strong and weak stations, long and short 
antenna.



Cleared the audio stage, the audio is distorted from the IF going into 
the 2d
detector.  Confirmed with a demod probe and signal tracer.  What would
cause audio distortion out of the IF?  Tried changing the IF tube, no
change.  It's not really that severe, just want it as perfect as 
possible before giving it back


Thanks, Bill
On Sat, Sep 09, 2017 at 08:55 PM, Al Klase wrote:
Just remember

Reply = Poster

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_________________________________________________________


     Bill,



     Well, this is pretty disturbing.  Clearly there are errors in the
     documentation, and maybe the original wiring.  Can you say FUBAR?



     I'd disconnect the oscillator cathode from the rest of the circuit,
     and ground it.  The slider on the volume control raises the 
cathodes
     of the !st Det and IF above ground, while their grids are at ground
     for DC.  this should, indeed, effect RF/IF gain control:  more
     cathode voltage = less gain.  BTW, 35's are remote-cutoff tetrodes,
     so they're intended for this sort of operation.



     The alternative would be to leave the oscillator cathode connected
     to the volume control, and clear any ground on that circuit node.



     Good luck,

     Al




On 9/9/2017 6:37 PM, William S Zukowski
       wrote:




       Just remember
Reply = Poster
Reply All = Everyone

_________________________________________________________






       Just restored an AK 80.  After replacing all the caps, noisy
       resistors, two bad tubes, most of the rubber wiring that had most
       of the insulation gone, it actually works.






       My question is about the "volume control" (see schematic): It's 
in
       the cathode circuit of the oscillator, so when it's adjusted, it
       sounds almost like a regeneration control, oscillating, etc..  It
       also looks like the schematic is wrong.  It shows the cathode
       grounded, which would negate any effect of adjusting the 
control. 
       It's not grounded in this set.  The radio is basically untouched,
       except for two electrolytic caps already replaced.






       Thanks, Bill







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     --
Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/ <http://www.skywaves.ar88.net/>


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