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Post by paradisecs on May 27, 2018 21:20:27 GMT
I was looking at driver boards on a few different SHP3s. A few of them have a .01 Ceramic capacitor across the emitter and base of Q5116, RT PNP Driver. I don't see this labeled on a parts list or parts locator and it doesn't appear on all of the driver boards. What is it for? I assume it is in place of C5146 but why move it closer to the transistor and jumper it to E & B rather than just use the C5146 point?
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Post by robnyc on May 27, 2018 23:11:15 GMT
I don't have any specific instructions on that mod. When you see that sort of thing it is because the design required neutralization to avoid oscillation. In other cases the design may be prone of allowing strong RF interference to leak in.
In both cases even the short distance of the traces on the board can be still long enough to act as an antenna. The wavelengths involved can be -very- short but saturate the finals and destroy them.
RobNYC
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Post by Ron Rich on May 28, 2018 0:50:51 GMT
Rob is 100% correct here --C-46 should be re-positioned on all of the driver boards, as the factory found that circuit oscillates. The space that it occupied should be left vacant. Ron Rich
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Post by paradisecs on May 28, 2018 3:54:54 GMT
Great to know. It figures that the only working amp I have is the one that isn't modified.
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Post by Ron Rich on May 28, 2018 11:57:57 GMT
Simple, just re-position it any time you see the space occupied--be SURE that two caps are not used ! I usually tack them on the foil side of the board, down flat. I also draw a line thru the silk-screened indicator. Ron Rich
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Post by robnyc on May 28, 2018 16:16:44 GMT
as the factory found that circuit oscillates. The space that it occupied should be left vacant. Ron Rich It doesn't surprise me. The architecture was fine, sandwiching a high gain section between to power stages w/no shielding is asking for instability. They should have just scaled-up the driver section of the TSA series and converted to silicon finals. The design work could have been done in about a hour and a lot of the old wives tales about the SHP's avoided....And that fusing..... RobNYC |
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Post by paradisecs on May 29, 2018 21:47:07 GMT
Thanks for the info. Got the cap moved no problem.
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