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Re: Kustom Semiconductor Replacements [message #21554 is a reply to message #21543] Sat, 27 September 2014 12:28 Go to previous message
Jerrybass1955 is currently offline  Jerrybass1955
Messages: 45
Registered: August 2014
Location: NC
Member
Very good to know! I'll update the list I am creating.
Not sure if I will be replacing that or not, but wanted to be ready. I haven't been able to work on it for a couple of weeks, but when I worked on it last I discovered one side of the power amp wasn't working. I replaced the 100 and 470 ohm resistors in the driver circuit and when I powered it back up I accidently "let the smoke out" of R205. In circuit most things seem to check out OK, but I was going to check out the protection circuit next and replace the driver transistors which are quite mismatched. The power transistors check good on a transistor checker and are pretty well matched. The diodes I was concerned about were CR107 and 108 (in the K100-2 1970 schematic.
So far, I pulled the 1ohm 5/W resistors and they read .81 and .95 ohms. I have a couple that read .85 each that I am going to replace them with. The 510 ohm resistors are drifted up to about 560 and 580, but I don't have any on hand. Gonna get some next week and replace them too and check check out Q129 and 130. Not sure what could turn on Q128 hard enough to fry R205 though unless I replaced something with a wrong part value that is dragging the base to the neg supply. Have to check that, and I am also trying to document the circuit diagram for the area around the elusive Q131 that I don't have.
Lots of adventure with this amp!

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