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Re: Kustom 100 blowing fuse [message #27277 is a reply to message #27276] Tue, 23 April 2019 18:00 Go to previous messageGo to previous message
JDinPA17603 is currently offline  JDinPA17603
Messages: 69
Registered: May 2018
Location: Lancaster, PA
Member
timetraveler I am a little confused so I am offering this to you for reference. I know how confusing and frustrating this can be.

Driver transistors
Q4 is a NPN 40409 equivalent is NTE128
Q5 is a PNP 40410 equivalent is NTE129
They can be had as a matched pair by ordering NTE129MCP
NOTE: the correct transistor must be installed in the correct position
Both of the driver transistors must have a heat sink installed on it and care must be taken not to short the heat sink to any nearby components.

Protection circuit
Q6 is a NPN 2N3567 equivalent is a 2N3567 or a NTE123
Q7 is a PNP 2N3638 equivalent is a 2N3638 or a NTE129
Note as with the driver transistors these must be installed in the correct position.

Output circuit
Q8 and Q9 are NPN 36892 equivalent is 2N3055 or NTE130
I recommend a matched pair - order NTE130MP
THESE ARE INSTALLED with a mica washer between the transistor and the chassis with heat sink grease applied to both sides of the mica film washer ... between chassis and washer and between washer and transistor.
They also use nylon washers and bushings to isolate the case from the chassis.

Diodes and electrolytic capacitors must be installed in the proper orientation.
Resistors should be as close as possible to the correct values.
Check for accidental shorts between traces on the board.
With the 1N3754 make sure that the leads are not broken or shorted to the clip or each other And insure that the diode is securely fastened in the clip.
All voltage measurements are with no load (speakers disconnected), no signal input (all plugs unplugged from the inputs) and all controls full up.

Since you are having an issue with parts continuing to blow, as others have suggested, use a light bulb limiter (100 watt incandescent lightbulb) wired in series with the power cord) and decrease the amperage on the fuse until you get this straightened out.

Good luck with the amp.

John

Old Us Navy Vietnam Vet
Playing for my own enjoyment and irritation of the neighbors.

[Updated on: Tue, 23 April 2019 18:28]

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