Bias circuit capacitors

Bias circuit caps

Here's the new capacitors from the bias circuit. You can also see the 'pegged' bias pot. I'll be replacing that too.

Next on my list of ‘replace old components’ are the electrolytic capacitors present in the bias circuit. Doing this was an ENORMOUS pain in the arse as the PCB in the 2204 is by its very nature, soldered underneath the board. This meant I had to un-bolt the board from its 6 posts (luckily I had a nice screwdriver/wrench for this) and attempt to lift it away from the chassis. Clearly this had never ever been done before and I’m sure the board was first bolted in and then wired up to the tubes/pots/power. Marshall did not have the foresight to make the wires long enough to be able to lift the board and work on the underside. I made a note (just with a piece of paper) of the wires emanating from the edge of the board, and where they were soldered to. This meant I could de-solder a few of them, thus providing better access. It only took a few lengths of wire before I could turn the board over enough to get access to the bottom.

Once done, I hooked everything back up and fired her up. All was well, so I went ahead and checked the bias, which hadn’t changed at all. You can see in this photo the bias adjustment pot at the end of it’s track, so to speak. I will be checking the value of this in the future, and perhaps replacing it.


2 thoughts on “Bias circuit capacitors

  1. Mark says:

    I know it’s been many years but I may save someone some agro. On the 2204 and 1987 models, I’ve been able to flip the boards quite easily by removing the knobs, and nuts of the pots and the inserts of the jacks. Then the whole thing just flips back. No need to unsolder everything. Having a nice set of socket drivers helps avoid scratching the faceplate, but you can do it all with a pliers if you are careful.

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