I've had a AA-151 for about 10 years now, just sitting on the shelf. A friend gave it to me, it's been sitting in his barn for several decades, it was there when he moved in. It worked but is very noisy and dirty (lots of poop in it) . I cleaned it up, tried to clean the sockets, but it's still noisy. especially when you wiggle a tube around.
In the process of recapping it, I found one black cap that was making noise by itself. After replacing them I was testing it, and found that the treble tone control adjusted alot lower that it was supposed to, down to 600 Hz. A capacitor on the tone assembly between wires 1 and 3 is 0.0022mf. It should be 220pf. So I'm going to replace the whole assembly with "The Brimar Circuit" and replace the tone controls with 11 position rotary switches.
I just got in a set of sockets for it, and am installing them now. My EL84s are very aged, so I'm thinking about replacing them with Russian EL84Ms or
6P14P-EV , because they can handle the 400 volts.
I also am going to replace the 2 x 6AN8As with a 12AX7 and 12AU7 like in Shannon's ST35 mod.