LabSeries L2

[travis4prez]

Hi Kids

New here and I have an L@ that I'm working on for a buddy. I was able to disarm the bogus home fix it job and get the amp to fire up. Found a schematic for an L5 on the web and followed that for the main power wiring. The problem now is that one of the transistors keeps smoking. I haven't let all the magic smoke out. It still fires up and plays, but there is this one transistor that keeps heating up. any idea why? None of the wiring near this board looks like its been touched in 30 years.

[J M Fahey]

No idea without more data.
Post some gut pictures.
I *think* the Lab2 is a Bass head, made by stripping one of the guitar ones of its reverb and fancy equalization.
So *maybe* an L5 can be a close enough reference. Or not.

[travis4prez]

Guts galore.

So apparently, I can't type. It is an L2. Not an L@. I have a schematic for an L5. It helped me get things together enough to power it up and get a few notes through it. I'd hoped someone would have one of these and maybe had the same problem but got it fixed.
After the post yesterday, I discovered that the  transistor in question was not soldered in. I took care of that but it still heats up. I'm thinking that someone replaced it but didn't bother to put in the right type. Any idea on how I can check that and what the right type may me?

There is one other problem but I don't believe its related. If you follow the black & white twisted wires to the middle of the power amp, they connect to something. Sorry, I don't know what it is. Those wires were plugged directly in to the 120v mains. That didn't seem kosher to me so I snipped the wires. Any idea what that thing is and where it should be plugged in?
Sorry guys. I'm a tube amp kinda person and not real comfortable with all these PCB's, heatsinks, & transistors but this an amp a buddy picked up and brought to me to look at.http://www.ssguitar.com/Smileys/default/uglystupid2.gif

[J M Fahey]

I'm thinking that someone replaced it but didn't bother to put in the right type. Any idea on how I can check that and what the right type may me?

Yes, use the schematic.
I see 10 power transistors (WOW !!  ) so its power section must be the same as the L5 one.
In that schematic you will have 2 versions , the 100W and the 200W ones.
Most parts are the same, except power transistors (normal or beefier), supply voltage (lower/higher) and maybe filter caps.
Now I´m quite sure L2 is a stripped L5.
Good for servicing.

There is one other problem but I don't believe its related. If you follow the black & white twisted wires to the middle of the power amp, they connect to something. Sorry, I don't know what it is. Those wires were plugged directly in to the 120v mains. That didn't seem kosher to me so I snipped the wires. Any idea what that thing is and where it should be plugged in?

Weeellll , if Gibson put it there, it must be for something.
I bet now your amplifier does not turn on. 
Leave it back as original, it´s a thermal switch which cuts power off (hence the 120V mains connection) when the heatsinks get too hot (that´s why it´s bolted to them).
If the amp works, do the basic "mechanical" maintenance such as clean pots, jacks and switches, blow the dust and give it back to owner.
Good luck.

[Enzo]

Wow.  Not comfortable in solid state?  ANswer me this:  if you encountered a tube amp with mains wiring running to some part you didn;t know, would you just snip that out too?

[travis4prez]

Thanks JM. I suppose I'll have to use the layout along with the schematic to figure this out. Nice call on the thermal switch. I would have never thought of that.

Enzo, I haven't had that problem with a tube amp. Caps, resistors, pots, & tubes is all that's in there. Once in a while you might find a diode rectifier but that's about all the sand found is in any tube amp I've worked on or built.

Thanks

[joecool85]

Travis, is the amp working now?

[travis4prez]

Well, no. Looking at a computer screen and translating that to the amp is not my forte. Gotta print out the schematic & layout and try again this weekend. I can draw on those to keep up with where I am.

Thanks