A look inside an unmolested Fender Bassman 100 Amplifier


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It's unusual to get an amp like this in for repair that doesn't seem to have been repaired before. Internally at least. The output valves look a bit scary.
There are signs that it has been stored in a slightly damp place for about thirty years.
And it has been dropped on its end, so I have a bit of metal bending to do. I don't think the transformer will have internal damage, but it could be damp inside so I am going to warm it up for a few days with DC through the speaker windings. The choke and main transformer will be included somehow so they get some too. I will probably end up with a large amp-shaped magnet, but that's easy to fix.
Here we see that one of the 100 ohm resistors has burnt slightly. It's a bit worrying that just one is affected. Probably nothing but this will need to be checked out very carefully.
The white stuff is from wax. An "aqueo-oxidative efluxulation of the stearically-derived impregnatory matter" is what the little kids round here call it.
One of the caps has puked. These are all going to go.
I don't get enough of these amps in to make it worthwhile to hold a stock of parts, so I get a set of valves and caps from http://www.tubeampdoctor.com/ . They provide a very efficient service, just send them 250 europounds and a couple of days later they turn up, decent quality and well matched tubes. Very time saving.
The new electrolytics are considerably smaller and lighter, and it's essential they are held in place firmly or over time vibration will cause failure from metal fatigue in the leads. These are held down with Gorrilla Glue.
I will also be adding extra foam inside the cover to make sure.
I have replaced the fuseholder with a 20mm version rather than get one similar to the original. This one has better clearance from the edge of the chassis, which is good. I have fitted a 2AT fuse instead of the original 3A.


Fender were a little confused about how we do mains stuff when they made this. The blue wire went to the fuseholder and the brown went to the switch. Also the switch is double pole, where we would normally have a single-pole for this job. I have rewired the correct way, but left the switch in its double-pole configuration, I think it does no harm like that.
A lot of new caps, and a cleaner board.
Almost all the resistors were OK, and so were the pots after a clean. Not really surprising, the pots are fair quality, and guitarists typically don't mess with amp settings much after they find what they like.
Valves lit up for a test run and bias check.
Resulting in screen resistor unhappiness, so replaced them all.
Back together again. Will look better with a clean of the front panel.