do I really have to pull the ckt bd to change the PT in Ampeg B15?

[marku52]

So I've got an intermittent short in a PT of an Ampeg B15, I'm trying to pull the PT to see if it is fixable, and the wires are so stuck under the ckt bd, I'm wondering if I have to pull it to get the PT out?

If anyone has done this before, please give me a little insight.

Thanks!

-steve

[52 Bill]

If anyone has done this before, please give me a little insight.

I've replaced a few PTs in B-15s and have never had to pull the board, if fact I don't think that you really could pull the board out. Everything is very tight in there and if the pc board is mounted a bit out of alignment it will make even removing the mounting nuts difficult.

Remove the 4 mounting nuts and try pulling out the wires as you remove the transformer from the chassis.

[Leo_Gnardo]

As 52 Bill says. And sometimes it's near impossible to get a nut driver on those transformer mounting nuts due to small or misaligned holes in the circuit board. Here's where a Dremel or similar tool comes in handy. Grind away a little of that circuit board until you can fit your socket or nut driver in, then you're good to go.

If you choose to replace the transformer, shell & all, it's beaucoup bucks as I'm sure you know.

If you want to re-use the shell, it's a tedious & messy job. I've done it a few times. Melted the tar-like wax with a charcoal hibachi. What an awful job, but you can save @ $100 or more compared to the transformer-in-shell. The heat will wreck the paint, but then you can repaint the shell as you like. I did the last 2 with VHT wrinkle black and they came out looking good as new.

[Ted]

Dremels, long nose pliers and improvisation are the way to go. It makes it easier to get the PT out if you cut the wires close to where they feed through the chassis.

You can get the PCB out, you have to unsolder all the valve holders (you usually have to do this to change the output transformer). Fortunately B15s are tough enough to stand having these bits unsoldered and soldered back. I've done thirty or so PT replacements in the last few years and have never had to remove the PCB.

If you want to reuse the shell, the potting pitch melts at around 70C. Using an oven set to 100C you can unpot the tranny without taking the paint off. I've got a little electric oven I use for this - you probably don't want to use the kitchen one as Coal Tar pitch is a) toxic and b) hard to get off.

Its actually possible to get the mains transformers rewound - you can get modern nylon bobbins that fit on the old iron. Separating and cleaning up the laminations is a nasty job.