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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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In Reply to: Heathkit AA-121 * PT hum * Coupling cap question posted by lektrik on January 13, 2015 at 21:22:26:
The coupling cap and the ground reference("grid leak") resistor on each output tube form a high-pass filter, with –3 dB frequency 1/(2πRC). For example with .047 µF and a 220K grid leak you would get –3 dB at about 17 Hz and 6 dB/octave roll off below that. There would be phase shift well above 20 Hz also. I'm not saying this is the only reason the amp sounds thin, but larger coupling cap values could be part of the solution.
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Follow Ups
- .047 µF is definitely small for a coupler - JJ Triode 22:29:55 01/13/15 (4)
- RE: .047 µF is definitely small for a coupler - Sherwood Forest 09:54:57 01/23/15 (0)
- RE: .047 µF is definitely small for a coupler - lektrik 05:13:15 01/14/15 (2)
- RE: .047 µF is definitely small for a coupler - sony6060 06:35:33 01/14/15 (1)
- Changed couplers.........better now. - lektrik 09:01:54 01/17/15 (0)
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