Richard,
I think the Product Detector mod is quite worthwhile.
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If you've ever used an R-4 or R-4A(13 tube) you will notice its? VERY nice and slow AVC on ssb.
You can see the s-meter virtually hang on the highest audio peaks.
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Drake eliminated the tube product detector and went to two diodes in the 11 tube R-4A and kept it to the last R-4C (I believe).
It was simpler, solid state but it caused detected audio to get back into the AVC, making it into a Fast (or medium) AVC.
You can watch the s-meter dance around on sylables and hear the harsher audio as noise is allowed in between sylables.
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Rob also found problems like the signal exceeding the BFO on AVC attack (if I recall correctly) and that may be.. but that's
above my pay grade, I never noticed that.? But now my R-4B sounds like my old 13 tube R-4A with its slow AVC.
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I gave away a lot of boards, someone may be able to give you one.? I might have a few more if I can find them after my move.
My board is SMD.? The NE-602/SA-612(?) is now obsolete, you might have to get some from china?
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73,
Gary
WB6OGD
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Gary WB6OGD