Old LectroLab Amp - worth buying?

[johnnyreece]

So, there's a lady at work that wants to get rid of an old tube amp. She stopped by with it, but I didn't have much time to mess with it. I can't find any information on it, other than this page (top two pictures match this one): https://lectrolab.wordpress.com/lectrol ... s/unknown/

It also seems quite similar to this Valco: https://reverb.com/item/5180042-1940-s- ... super-cool

There's a stamp on the bottom that appears to say Model G4SC, although it *could* be G48C. Neither give me any hits on the interwebs. My best guess is that it's a R100. Tubes appear to be 6J5, 6SC7GT, 6V6GT, and 5Y3GT.

Now, the fun part: She wants to know if I want to buy it. I really don't need another amp, but...what do you all think it would be worth? I have no clue if the PT/OT/speaker are any good. It's going to at minimum need a recap and a cord. I'd probably try to draw out the schematic to see what the heck it even is...I appreciate any insight you have!

[Phil_S]

I really don't need another amp, but...what do you all think it would be worth?

Every guitar player needs another amp. What were you thinking?

What's it worth? Hard to say. I might offer her $50. If she was thinking $500, she's dreaming. People do that. Old <> valuable. I might go as high as $100, but that would require a good speaker, too. Remember, you will be putting time and parts into it to get it properly serviced and safe.

Do you think she might allow you to keep it for a week to give you a chance to check it out? Whatever you do, be careful! Bring it up to full power on either a dim bulb limiter or a variac.

I think maybe you got a good hit on that Valco, but that price is for what seems to be a properly serviced and working amp.

[johnnyreece]

Yeah, I was thinking maybe $50, but I'm currently working on that radio amp (with an interruption to work on chimney flashing and gutters last weekend). It's missing the rectifier, so that's another (albeit minor) cost. If the 6SC7 is bad, those are pricey (unless I wire it for 6SL7). Lots of ifs. I like the idea of asking her to borrow it. I've got a dim bulb tester I could bring it up on. That should at least let me know if the trannies/speaker are shot. I could also test the tubes.

[Phil_S]

Rewire for 6SL7 is a good idea. I've bought what appear to be NOS or ANOS on eBay for very little money. Ask her if you can borrow it a while to evaluate it. It's not as if she's got another buyer and it's taking up space she'd like to recover. Ignore that other project you've got underway. Eventually, you'll get to this one. It doesn't matter how long unless you expire first and even then, it doesn't matter. I've got at least 3 old amps that need some kind of conversion and whatnot. I've had them for years waiting for me. One is an old public address power amp, in early new condition with original ANOS 5881's. I find it comforting to know I won't run out of projects.

[johnnyreece]

Ignore that other project you've got underway. Eventually, you'll get to this one. It doesn't matter how long unless you expire first and even then, it doesn't matter.

Your avatar is perfect. You're that little devil on the one shoulder telling me what I want to hear! I may have come up with justification for this: My brother's birthday is coming up, and he's a gigging musician. Birthday present!

[Phil_S]

The avatar is Phil, Prince of Dim Light, from the comic strip Dilbert. The artist is Scott Adams.

[johnnyreece]

Thanks for clearing that up!

So...I bought it. I'm having some regrets, as someone else has done some of their own "mods" to it. The electrolytics appear to be original, but there are a couple orange drops that are old, but definitely not original. The rectifier socket seems to have been rewired at some point (although, no rectifier was present). It seems that it was wired for a loctal 7Z4 or something (plates are pins 3 and 5, filaments 6v and pins 1 and 8, cathode pin 7). It seems the 5v tap was taped off, so maybe it's cooked. What I thought was originally a 6SC7 appears to have already been swapped for another dual triode. Seems to be an odd setup, though. Plates and cathodes of each triode are paralleled, but each (identical: no hi/lo setup) input goes to its own grid. The volume control is also strange...aside from the outside lug to ground, like normal, the other outside lug goes directly to the power tube grid. The wiper is also connected to the grid by the grid stopper and coupling cap, which is somewhat normal, but there's no grid leak. Or, I suppose maybe the pot is set up as the grid leak in this setup...thinking out loud. This is looking more and more like a prime candidate for a gut and restuff project...

*edit - Gut shot posted.

**edit 2 - looked at it, and sure enough, it's a loctal socket for the rectifier (appears factory, too). That's coming right the heck out of there...maybe the 5v tap isn't shot after all!

[johnnyreece]

So I traced out the schematic, and found some weirdo stuff. After a recap, I fired it up. I had a 7Y4 kicking around, so that's working for now. Everything seems to work except the tone control. I wasn't sure what was in the first slot (print was worn off the glass), but it was wired for a 6S_7 tube. Using a 6SL7 is too hot (howling as soon as you turn the volume up). 6SN7 is in now, and sounds fine. Anywho, I may move to the technical discussion section with this shortly, as the whether to buy it question has been answered!

[Phil_S]

It's a bit of a rat's nest, but schematic shows not many components. When you change the e-caps, you'll reclaim some space inside. I like it!

[johnnyreece]

Yes, it's been recapped, and it's a lot cleaner looking now. I went ahead and started a new thread in the technical discussion section. I need to fix the Tone control, then I can work on reassembly. There's another cap in the NFB circuit I need to get ID'ed, but I think it's pretty much traced out. Lots of interesting tricks I wasn't too familiar with in this, so it's been a fun learning experience!