Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

Re: Carlsbro GLX 80 (Special Edition) schem, please!

8/29/2004 7:02 PM
Re: Carlsbro GLX 80 (Special Edition) schem, please!
Hello, Enzo. At least one of the three leg regulators, on the suspicious board, is bad. I'll try to find a replacement for both of them tomorrow.  
Then I'll plug the amp to the variac and watch if something else is bad (Thank you to you both for this reminder).  
I have checked all diodes and transistors and they seem to be ok, but I won't know how are the rest of the chips until I have replaced both regulators. There's a long HEF4053BP analog/digital thing with a lot of legs and about eight more smaller ones like the 4558.  
Thanks again to you both.
And now, a word from our sponsors:

8/29/2004 7:22 PM

I have fixed alot of amps that have the same xstrs. I fixed a music man one time, and it had a bad bypass cap like Enzo is talking about and it keep smoking the fuse in ps. If it did,nt have a fuse it would have done what yours is doing.  
It was hard to find inthat the tip of the top was burnt. I really had to look to see it. The bad thing is almost all if not all seem to have a black spot on top. On some opamps, they will crack in the center and it is hard to see. I use my to find these less obvious shorts it,s a safe way to find them.  
Thanks for jumping in Enzo. How are you doing? I have to get over to see you sometime as close as I am to you.
8/30/2004 6:28 AM

>Any with a small black divot missing are bad.  
>It was hard to find inthat the tip of the top was burnt. I really had to look to see it. The bad thing is almost all if not all seem to have a black spot on top.  
Excuse me, where should I look to see these dots?
8/30/2004 5:30 PM

What you are looking for in that case is a small spot that looks burnt. When the part shorts out, it gets very hot inside and the pressure will blow a tiny hole in the thing. Usually looks like a black dot. SOme parts have a dot of black paint on them for whatever reason, and it can look similar. So you have to look close to make sure the failure does not look like the paint.  
On many boards there is a small cap - really small - for each IC stretched between the + adn - rails there. SOmetimes there is only a cap for every few ICs. Roll wiht the punches.
8/31/2004 3:55 AM
ok, variac, and no heat but still big short somewhere; the board is quite acceptable quality, so I begun to pull opamps out, and with all them desoldered from the board still there was a short. I happened that a pair of small transistors (a pair: npn & pnp) were both shorted (emitter to collector short). I believe they have something to do with the reverb (no schem, remember?), and I would like to ask if there is a way to test in cold the reverb tank and if this part is capable due to a short or something like that to damage the circuit. I mean I'll change the transistors but would like to know if the reverb caused it. There are a couple of diodes conected to the emitters and a pair of overheated but ok 100 ohm resistors to the bases of this transistors.  
Now that I am in to it I'll check everything again and change suspicious components.  
Thanks again.  
8/31/2004 6:39 PM

If both output xstrs are the same polarity, they are not likely in parallel, they are what we call quasi-complimentary, rather than true complimentary as with the NPN and PNP set up.  
SOme reverb drivers are in fact a small push pull pair, and if those xstrs are shorted it could load your rails. The reverb pan can be tested with an ohm meter. At each jack, measure resistance. Open is bad. The resistance will not be wrong, we are just looking for open or not. The one end may read less than an ohm and the other end maybe as much as 200 ohms.
9/23/2004 11:23 AM

Does it matter which end of the reverb tank goes to the reverb send / reverb return in the circuit?  
I mean, is the 20 ohms end of the tank the IN or is it the 200 ohms end?  

<<First Page<PrevPage 2 of 3 Next> Last Page>>