Bassman Modifications

Posted on Feb 4, 2014

Changing to a 3-prong AC cord is pretty much an expected upgrade or mod, as is replacing the filter capacitors. Changing the coupling capacitors to Orange Drops or some other boutique brand is also accepted, and often adds to the hyperbole in eBay auctions. Anything else (i. e adding a `Soul Control` to the back of the chassis) is open to the whims and fads as set

Bassman Modifications
Click here to download the full size of the above Circuit.

out by the vintage community. Your mileage may definitely vary. ere we`ll have a little chart with the various Bassman circuits to be found today. There is no real `trick` in determining which circuit you have without taking the chassis out. The tube chart seen inside the `box` is a good indicator, but not 100% accurate. It was common to `use up` 6G6A charts, as an example, even if the circuit inside was a 6G6B. I have worked on many AB165 Bassman heads (and personally own one) that `feature` the AA165 tube chart. Most web sites will have us dating our Bassman head to the hour it came off of the assembly line from external appearances, but few explain how to determine the internal circuit. This is probably because there is no easy way to tell. These are just basic guidelines, and we`ll need to dig deeper to find out what we really have, and if it will suit our purposes. Keep this in mind as well; starting about 1977, output power was increased on many Bassman heads from about 40-watts RMS to about 60-watts RMS. This means transformers, power supplies, and filtering circuits will change, yet it can still be referred to as `AB165` (as an example). The chart above, although neither authoritative nor complete, is still helpful and interesting. For my money, the `best` Bassman head would have to be the AA864. This would give the least amount of `work` involved in order to have a very good guitar amplifier. The `worst` candidate...

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