Vintage Ampeg BT15 Help

[erock0138]

Greetings,

I just got an old ampeg bt15 that's in need of some serious TLC.

I took the cover off and noticed there are 2 components that have essentially dissolved. (Reference pictures)

I got the schematic from Ampeg (Surprisingly easy!) And it looks like the unidentifiable 2 components are a part of the diode bridge, considering there are only 2 still in tact there now. (But are both different types)

Am I correct by the looks of it?

Also, Haven't powered the unit up (Obviously) It had a 30 amp fuse installed, which has really got me worried. It calls for a 4 amp.

Any help would be greatly appreciated!

Thanks again .

[soundguruman]

the file format of the picture I could not access, try JPEG or GIF instead?

[erock0138]

noticed images didn't attach correctly, I'll try to upload them again soon.

[erock0138]

IMAG1181 2.jpgIMAG1187.jpg

[erock0138]

IMAG1186.jpgIMAG1181 2.jpg

[erock0138]

IMAG1186.jpg

[Amp Kat]

If those are bridge rectifiers something caused them to open up which I would think likely a shorted transistor or at least faulty. The fuse should be a 3 amp not 30 so yes get that squared away also and replace with correct one. I would take all of the TO-3 transistors out and check with a diode meter for shorts or opens and check the other transistors also. If you find bad ones replace them then hook it all back up and get out that lighbulb limiter and see if it will fire up. I would probably try to fire it up without the TO-3's back in and make sure the power supply is ok and you get that 78 volts or close on the sockets.

[g1]

It had a 30 amp fuse installed, which has really got me worried.

Me too. To paraphrase what someone else on the forum said recently, the power transformer may have "saved" that fuse. If those diodes (or something else) were shorted the fuse would have blown. If someone then installed the 30Amp, the power transformer would probably blow before the 30A fuse would.
So, before spending much time on the amp, verify that the power transformer is ok. With the 2 blue wires disconnected from the circuit, you should measure around 56 volts AC between the 2 blue wires.

[erock0138]

If someone then installed the 30Amp, the power transformer would probably blow before the 30A fuse would.

Yes, that was my fear.
Thanks everyone! I'll give an update tomorrow when I have some more time with it.

[JHow]

Also, Haven't powered the unit up (Obviously) It had a 30 amp fuse installed, which has really got me worried. It calls for a 4 amp .

This must be going around. I just bought a Plush 1060 off a guy (it's "dead"). I asked him if it was blowing fuses. He said "no". I open it up to find a 15 amp fuse (it takes 2.5A).

[Jazz P Bass]

I have seen on some pieces of equipment where they put a fuse inside the chassis, in series with the external fuse.
Act stupid & put in the wrong value in the external fuse holder: Gotcha!

[soundguruman]

I have seen on some pieces of equipment where they put a fuse inside the chassis, in series with the external fuse.
Act stupid & put in the wrong value in the external fuse holder: Gotcha!

How many amps is a penny?

[Amp Kat]

In this case I really doubt the power tranny is bad because the diodes opened up which really acted as the fuse and a SS tranny with higher current hence bigger wire is harder to fry than the smaller wire in tube HV windings but I guess it could be bad but really doubt it.

[erock0138]

I did just test it, and the tranny is fine! Thank goodness. I disconnected it and got 60 volts.
So, I replaced the diodes, put in the correct size fuse, and also tested the transistors, (All checked out fine with the diode function on my meter)
So I decided to fire it up, and the fuse blew instantly. So, next I'm going to take out all of the transistors (They just screw down and plug in, not a big deal) And see if it blows.
I'm also concerned with 3 of the large capacitors. They are 2500 UF 80 volts. They would be my next guess. Each one of them has a hole under each, as in the picture, like it got hot and melted? But the silver top is still intact.


Edit: Any Tips for testing these? I have a capacitor function on my fluke 110, but haven't taken them completely out of the circuit to test yet. Also, looking for some replacements just in case, and found some that are 100 volt rating. Will they work without much compromise if 80v are obsolete now a days?

Thanks again.

[olddawg]

Every time you blow a fuse you are stressing the PT and wherever in the circuit the excessive current is being drawn. You need a variac with an amp meter or at least a light bulb limiter. See if you can float the power supply. If your rails are stable and you aren't blowing a fuse the caps are probably usable. Once you find the problem, then check for ripple under load. Pulling the outputs is a good idea. Just remember to keep any insulators straight and you have to use heat conductive compound normally. If this thing was abused you could have blown drivers too.