[Collins] Re: 75S-1

[kiyoinc at attglobal.net]

** Reply to note from Dr. Jerry Mon,  7 Jun 2004 19:45:39 -0400
(EDT)

> They can be discriminated apart by a critical ear, though an 
> oscilloscope on the speaker make that discrimination easier. The first 
> will be 60 Hz sinewave, no harmonics. The second will be a 120 Hz 
> sawtooth because the plate supply uses a full wave rectifier. The third 
> will be a 60 Hz sawtooth because the bias supply uses a half wave 
> rectifier. So by ear you have to pick the octave (60 Hz is close to B an 
> octave above the bottom of the standard 88 key piano), and the 
> harmonics. Or just replace the potentially suspect parts, the two audio 
> tubes and the filter capacitors.

Well, I slapped the scope on the audio and it's a raucous 60
cycle sawtooth.  I guess it's the bias supply.

Maybe I can get by with replacing the bias cap.

Mouser has 47 uF 160 V Nichicon electrolytic caps that measure
12.5 x 20 mm.  It looks like three of these might fit in the
aluminum can. 

The can is 1 inch in diameter and 2 inches tall. 

de ah6gi/4