[TenTec] [] Running a Century 21 on external 12V power

[Gary F]

Josh, I don't know what you mean by tropical fish capacitors but some capacitors are quite sensitive to noise pickup, as you describe, especially in high gain audio circuits like this one. This is the reason why some early capacitor designs were supposed  to be installed in a preferential direction-not because they were polarized but because they were fabricated in such a way that the last layer of the cap acted as a shield for the rest of the capacitor within.


I doubt that changing those caps will resolve your hum. Jim and I agree (I think) that reducing magnetic coupling is your best shot at the hum problem resolution.

Gary
Sent from my iPad

> On Jun 2, 2017, at 10:30 PM, Josh Gibbs <gibbsjj at gmail.com> wrote:
> 
> OK, I tried this trick and I found 3 'tropical fish' capacitors that buzzed
> like a SOB when I touched the 'probe' to the positive lead. 2 on the audio
> amp board, and one on the pre-amp board.
> 
> What should I replace them with? Did Ten-Tec use these because they possess
> some special property, or were they just cheap back in the '70's? Can I
> replace these with some mylar polyester film caps?
> 
> -Josh
> 
> On Fri, Jun 2, 2017 at 12:50 PM, Stuart Rohre <Rohre at arlut.utexas.edu>
> wrote:
> 
>> There is an old radio troubleshooting trick:
>> 
>> You use a insulated test probe, (length of solid wire set in an insulated
>> handle to safely handle it).
>> 
>> Move this to the plus end of each electrolytic cap, in turn, and see if
>> the hum level jumps up.  Likely that cap may have dried out and changed to
>> lesser value if you get more hum on one than others similar.
>> 
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