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Post by paradisecs on Jun 7, 2018 21:20:17 GMT
When replacing the bias pots, what value in ohms do you want them at before applying power? I'm assuming you want the most resistance so for a 100 ohm pot you want it at 100 and not at 1-2 ohms otherwise you run the risk of to much power?
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Post by Ron Rich on Jun 7, 2018 21:38:42 GMT
Steve,
When changing pots, use a dim bulb tester, change them one at a time, watch the bulb- As I said, I have never used Tony's method--but my guess is that the pots adjust out somewhere in the 10-20 ohm range ? Ron Rich
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Post by paradisecs on Jun 7, 2018 22:42:28 GMT
Thanks. I wasn't sure if the dim bulb would protect me from the bias being to high before I had time to adjust. I'm not getting anywhere with Tony's method of testing the ohms across drivers. Nothing adjusts correctly but I've tested all resistors and caps so everything seems fine. Guess it's time to blow something up.
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Post by Ron Rich on Jun 7, 2018 22:46:45 GMT
Steve,
I use a 100 ( actually, 95 miser) watt bulb, and have my Phillips screwdriver inserted into the pot, prior to applying power--so far, no problem--Ron Rich
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Post by paradisecs on Jun 10, 2018 20:31:08 GMT
Digging a littler further in to the amp I discovered Q12 was broken. It's Seeburg# is 309687. Aren't these the same as #309686? ( I have a ton of those) #309686 has a Ic of 50 mA while 309687 has Ic of 30 mA. Can I use the 309686 with the sightly higher value in place of the bad 309687?
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Post by Ron Rich on Jun 10, 2018 23:47:15 GMT
No --different gain--use a MPS A06. for either. A 309686 won't work for a 309387.
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Post by paradisecs on Jun 11, 2018 1:01:59 GMT
Thanks again Ron. I've been using the cross-reference out of Tony's books and the more I learn the more I'm finding out that there are a lot of alternate parts that don't seem to be correct; or at least have a large margin of tolerance that I wouldn't have expected.
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Post by paradisecs on Jun 22, 2018 20:21:52 GMT
I know you said that if the system is working don't change to a thermister based bias. If at some point I needed to change, what has to be done? Just change out the three three components under the heatsink for each side to match the schematics or is there more further up the line that has to be changed?
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Post by Ron Rich on Jun 23, 2018 2:37:41 GMT
I just replace the transistor--- Ron Rich
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