Hartke 3500 Hissing, Crackling

[Cameronsf62]

Hi all, I have a problem with my old workhorse Hartke 3500 bass head. I have been using it in our practice space for several years and occasionally gigging with it. The only work I have done on it in the past was to re-solder all the power transistors when I started getting crackling, a known problem on these amps.

A while ago I went to practice and turned it on, and got the sounds that you can hear in the linked video. Schematic attached also.




-Loud hissing and buzzing , mostly on the solid state channel, with no instrument plugged in

- Known good tube installed in tube channel

- no sound from any instrument when it is plugged in

- no change when a cable is in the effects loop

- noise changes when the EQ is in

- sound is changed when the contour and volume knobs are turned

- no noticeable burned components or bulging caps, main transistors do not get hot




I am fairly ok with electronic repair, I can measure voltages and solder pretty well, I am looking for some advice from anyone who has repaired this particular amp and may be able to assist me on what to check first.

[glebert]

My guess is a bad connection to the graphic eq, I would clean the switch and faders with appropriate cleaner/ lube.

[g1]

Also check solder on any connectors of the front panel board. We used to do a lot of connector resoldering on those amps.