More Weird Bassman Stuff

While I've been working on the I Am The Bassman project as yet to be named-I'm considering to call it a Cowpoke 40 or The Walrus with a nod to the beatle folks.....where was I ?

Oh yes. I've had an AB165 blackface Bassman in the shop for lots of bad noises and I guess it finally expired on the guy because it made barely a sound on the shop speaker.

On examination nothing seemed especially wrong but the more I fooled with it the worse it got.

I chased the  noise part and fought it to a standstill but the volume was still faint. After consulting the usual savants I put it aside to let my subconscious tackle the problem.

What could it be? I mean, there are only 11 parts in the entire amp. I spliced in another output transformer with no progress made. Same with the power supply diodes and validated the entire bias supply.

This morning I was thinking as I was validating every component and connection, what if those nice looking Sprague Atoms in the power supply were the problem? I mean, they passed ESR, and the voltages were correct in all the right places.

Sure enough. I installed a set of new F&T power supply capacitors and dropping resistors and when I warmed it up and threw the standby switch I was greeted with that nice thump you get when everything's working right.

So the first thing I did was I called the owner and told him he was going to get his amp back. He'd left me a message but I had my phone turned off most of the weekend so I could get some work done.

I should turn my phone off more frequently, I think.

UPDATE: As it turned out the cure was far more elusive than I had thought. This amp was a late 1965 build but it was sort of a hybrid that had been hacked, the end result being that it hummed and was low on volume. Why was I kidding myself?

So I decided to nut up and build it back to print. Starting at one side and working my way across to the other it was rebuilt to proper AB165 configuration, the connections were tested, and powering it up proved the point.

Sometimes you just gotta start from scratch, erase all the previous mistakes and hacks, and get a new baseline of known good parts.

It was all good drill for the AB165-ish project I'm working on at present..