1987 V1 Cathode Cap

hdahs · Post by **hdahs** » Mon May 30, 2011 5:32 pm

I've noticed on most schematics I have seen, that the 1st (V1A) cathode cap is listed at 320uf, but most of the layouts/pictures in the 50 watt instructions for 1987 builds show a 220uf cap. Which is correct, and in general, what difference in tone/gain, will there be between the 320/330uf, and the 220uf?

Thanks!

toner · Post by **toner** » Mon May 30, 2011 5:37 pm

Not sure which is correct but you won't notice any difference between them. Both fully bypass the cathode resistor way below audible frequencies.

hdahs · Post by **hdahs** » Tue May 31, 2011 4:06 pm

Thanks for the response. At what rating would you start hearing a difference?

toner · Post by **toner** » Tue May 31, 2011 6:07 pm

Since it's bypassing an 820 ohm resistor, you probably wouldn't notice much difference in caps until you get down around 5uF. As you decrease the cap size, the corner frequency of the high-pass filter raises so you begin to decrease bass gain.

Below are some examples when bypassing an 820 ohm. As you can see, anything larger than 10uF boosts all audible frequencies.

cap, corner frequency
330uF, 0.6 Hz
220uF, 0.9 Hz
50uF, 3.9 Hz
10uF, 19.4 Hz
4.7uF, 41 Hz
2.2uF, 88 Hz
1uF, 194 Hz

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1987 V1 Cathode Cap

1987 V1 Cathode Cap

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