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Need advice on which ceramics to replace with polyprop film caps in this circuit?

Posted by dickmc (A) on April 16, 2005 at 18:18:36

I am in the process of replacing over 150 sonic path and power supply caps in a 1970 Sansui Quad 65 watt per channel receiver. I am not sure an intelligent person would have started this, but none-the-less it is underway. Sonic electrolytics being replaced with Black Gates and power electrolytics with Nichicons. Sonic path ceramics are being replaced with polypropylene film.

I can figure out which ceramics to replace in most of the circuits. However, parts of the driver board have me stumped. I need advice about the ceramic disk caps highlighted in “yellow” on the driver board circuit shown below:

Some of the board voltages are shown in red. If you need it, a larger sized image is here.

Currently I think that the C03, C17, C19, C21, and C09 ceramic disk caps should be replaced with polyprop films. Is this right???????

Rationale is:

1. I assume that C03 is a sonic cap because of its location and the fact that at 20,000 hertz its “resistance” would be 80K ohms which is consistent with the resistors around it. Is this right to replace C03 with a film cap?

2. Is the ceramic disk C11 at 15pF merely some kind of power bypass cap? Should I replace it with a mica or simply leave it alone as an old disk ceramic? ...or is C11 actually doing some kind of sonic function?

3. C17 at 0.047 uF has a couple of volts across it and I assume it is performing some kind of sonic function. Thus, I assume this should be replaced with a polyprop film. Is this a good assumption?

4. C19 and C21 appear symmetrical and have only about a volt across them. I assume these should be replaced with polyprop films?

5. I have no idea what TR11 is supposed to be doing, but C13 at 100 pF has 45 volts across it. I assume this is some type of power function cap and should be left alone as an old disk ceramic?

6. Is it right to assume that C09 + R09 is some kind of pseudo partial crossover type circuit? If so, then the ceramic C09 should be replaced with a polyprop film?

Thanks in advance for any advice or comments.
Regards, Dick

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