[Collins] 75A2 Help Needed

[Dr. Gerald N. Johnson]

On Sun, 2007-09-23 at 17:33 +0000, david_box at comcast.net wrote:
> Gentlemen
> 
> A good friend has just acquired a 75A2 but appears that there are some front end issues.  He believes that the front end coils need replacing and is looking for a source.
> 
> If you can help out please contact
> 
> Ed Cole  WB0SUT
> EDWARD H COLE
> 6060 4 MILE CANYON DR
> BOULDER CO 80302
> Cell # 720 771-7258
> 
> 
> Or let me know and I will pass information on.
> 
> Thanks
> Dave  K5MWR 

Unless the front end has been hit by lightning coming in the antenna
lead in repeatedly with the band switch in a different position each
time, its unlikely the front end needs coils. Its possible the low band
coils were delicate to have gone bad from corrosion, but the high band
coils weren't so delicate. I'd suspect every other part in the front
end, especially band switch contacts, RF tube, and trimmer capacitors
before I'd suspect coils. Tubes are in sockets because they need regular
replacement. We know band switch contacts get oxidized and don't make
contact. We know ceramic trimmers do the same. Unfortunately vintage
ceramic trimmers also get stuck mechanically and that makes it hard to
tell if they are also open circuited where the shaft meets the terminal
piece. Sometimes ceramic variables can be disassembled and fixed and
cleaned (DeoxIT from CAIQ is good for those contacts and switch
contacts.) Takes just a fraction of a drop of DeoxIT on each switch
contact. Spraying the entire switch is not a good idea,  just the metal
needs cleaning and the insulation doesn't need to be soaked with
chemical.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer