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June 16, 2024, 03:12:46 PM

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Hartke A35 Repair problems

Started by Jesse, March 07, 2024, 10:38:03 AM

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g1

Yes, any transistors without plastic backs that are mounted on the heatsink need an insulator.
If the Q9 collector was in contact with the heatsink (ground), that probably explains the excess current through Q4 (via R97).

Jesse

Thank you! Things are looking much better!

Replaced Q4, insulated Q9.
Shorted input
No Load
Variac at full AC voltage 120VAC
1.03VDC across R97
0.29VDC at output

Is there anything else I should check before testing again with the 8ohm load?

g1

Sounds good.  Try it with load.  Some amps have trouble starting up loaded while on the bulb limiter.
If you get a bright bulb when you power it up loaded, you will have to power down, remove load, and power up.  Then (if bulb dim again) connect the load while amp is running.

Jesse

So far so good with the dummy load.
Variac at 120VAC
Sinewave at input
Very clean sinewave at output
Drawing 0.5 Amps at 50% Volume

I think I'm ready to try with the speaker next.

Jesse

It works! Thanks again g1!
The tricky part for me was missing the fact that the replacement part I purchased for Q9 had a metal backing, where as the original did not. See attached photo.
Any book recommendations for Electronics Repair / Troubleshooting?
Thank you again everyone! I look forward learning more here :)

g1

Quote from: Jesse on May 15, 2024, 02:21:50 PMAny book recommendations for Electronics Repair / Troubleshooting?
Lots of good suggestions in this thread:  https://www.ssguitar.com/index.php?topic=439.0