Hey Ethernaut ,

That is indeed the same amp. John Sawyer loaned it to another aspiring steel player and it died on him. He brought it to me to see if I could get it working again. At the time I had no idea what I was doing hence seeking help on the forum. The problem that I figure is a short in the amp section. I really didn't have any experience with amps at the time but I poked around on it for a while before I gave up. There should have been some new output transistors in the back of the amp. Some other parts blew off the board at one point and I hope that I replaced them with the proper ones. Anyway since then I have had much better luck with amps and have learned quite a lot. If I had known then what I know now I may have got it going again. Anyway I hope I put it back together well enough that you can figure it out. Good luck

OK looks like my last post was incorrect. I screwed up because I'm a NOOB. I didn't have the output transistors installed when I powered it up and measured voltage. After I put them back in things changed drastically. The current limiting lamp is bright and the voltages are way different. +2.17V/-2.17V with 1.37V on the speaker out. I have checked all of the output transistors again and show good. I have checked all of the transistors on the board and they test good. Not sure what I'm missing.

I got me a limiter and got some voltage through this thing.

From the main caps to ground is +14.2/-14.2.
There is +13.2V DC on the speaker out

1) Will build limiter asap!

2) Not doing anything until I get limiter and can post some voltages from amp.

3) The schematic you posted is similar but there are several voltage differences. I don't know enough to be sure it will work as a reference.

Hi Roly, DrGonzo78, J M Fahey,

Thanks for chiming in guys. I do not have a limiting lamp but I will get right on building one before I do anything else.
I don't have a scope but I think I could borrow an old one if you think it would help. I have not hooked up the speaker since Enzo advised not to.

JM you are right on most everything you said. Pretty perceptive

1) It is a steel guitar amp. Came from a friend that plays steel and he got it from another steel player.

2) Built by Heilman electronics in Nashville. Serial NO 15. I think may be this guy http://bb.steelguitarforum.com/viewtopic.php?p=1084881&sid=50bc43207f3365895f900757367ece01

3) All caps are rated at 25V or 50V.

4) There are 6 power transistors 3 NPN + 3PNP. Mounted in sockets on large heatsink under chassis. Will post pics later.

5) There are 2 transistors on each side with heatsinks and diodes. (drivers???). I did replace those.

6) I will work on getting part numbers and pics and post everything I can soon.

7)Will build a limiter ASAP.

The combo currently has a JBL Professional 2220B speaker 16 Ohm wired to a 1/4" speaker plug. I doubt it is the original. I will get some pics of the cab, speaker, etc soon.

Thanks to all of you guys for helping me with this little project.

Hey Enzo,

I finally got back to this project after I got some parts in. Thanks for the pointers.

Here's where I am with it. I ditched the speaker. Still the same. I checked the rectifier. Checks OK but had another so swapped it out. No change. Reading +41.25/-41.25...seems about right since all caps are rated at 50V. I replaced the TIP41 and TIP42 transistors. No change. I pulled all the output transistors and checked again. All good. Any more ideas? I don't really know where to go from here. Not sure how to go about checking the bias circuit. This thing is hand built and not very easy to work with. Wires everywhere

A friend dropped by an old (early 80s?) solid state amp that was blowing fuses. I confirmed that and then he told me that the volume was not as loud before the fuse popping. So I thought it would be an easy fix. I started with the output transistors and found 2 out of 6 bad. I ordered a new full set and put them in with new isolators. Still blowing fuses. I hooked it up to the variac and only got about 5V AC applied before the speaker started humming loudly. I'm guessing that something is shorted but I have no idea what or where to start. Any help would be appreciated. I have tools and am willing to learn. I have attached a couple of pics. Thanks in advance.