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Hartke 3500 question

#4
fast_frank_d said:
Hello all,

New bassist here with a noob question!

I picked up a Hartke 3500 head with a broke pre-amp and compression knob for cheap. Does anyone know what kind of potentiometers these are so I can replace them?

Thanks!
Frank D.
Click to expand...

You first need to determine whether your 3500 is one of the older MOSFET models or newer BIPOLAR models because the pots are different for each model.

MOSFET model:

Preamp pots: 10KB (10K, linear taper)
Compressor pot: 50KA (50K, audio taper, with a SPDT switch at full CCW rotation)

BIPOLAR model:

Preamp pots: 50K (50K, linear taper)
Compressor pot: 50KA x 2 (Dual 50K, audio tapers, with a SPDT switch at full CCW rotation)

The stock pots are soldered directly into the PC board, so if the replacement pots are not the exact size as the originals you will have to connect jumpers from the pot terminals to the PC board. The overall housing diameter of the new pots should not be larger than 18mm or so, or it will not clear the PC board. The bushing diameter must be ¼” in order to fit through the hole on the panel.

It’s probably best to order direct replacement parts from Hartke if you can, but as long as you use these values and sizes, then the generic replacements should work fine. Also observe the polarity of the compressor’s SPDT switch if you have to connect it with jumpers or the compressor will not work properly.
 

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