Lindell No. 603

[patlaw]

There has been some discussion about this amp in the schematics forum, but I wanted to move it here to get some input. The schematics I have so far are not even close. It's a five-transistor circuit, but nothing else matches.

The input transistors are 2SB54 germanium. With the input volume turned down, the amp is initially quiet, but the hiss increases with time. I'm thinking the transistors are leaking as they heat up. The 6" Pioneer speaker sounds blown. (I hooked up a different cabinet to test.) It's hard to tell since the amp is so crappy and low power. Does anyone know where I can get a 6" speaker for this amp?

At one point, I decided to trace the circuit board and create a schematic, but the axial components are standing up. That makes them a royal pain to trace and hard to measure values in circuit.

All of the electrolytics have been replaced. That got the tremolo going. Now, it still sounds bad. That's not a technical description, but I have to do some more investigating to determine what kind of distortion I'm hearing. It's not flat topping. The low frequency response is terrible below 200 Hz, but I don't know if that response curve is intentional. I've never seen one of these amps working, so I have no point of comparison.

Any thoughts welcome. I'm not charging for the repair, so it's educational at this point.

[galaxiex]

That circuit board and speaker looks very similar to some Teisco Checkmate amps.

Maybe the Checkmate 66 or 88, they both had tremolo.

Edit;

Here's a CM66 schematic.

[The Dude]

You might try the speaker on another amp to see if the speaker is part of the problem.

[vintagekiki]

Lindell No. 603

https://music-electronics-forum.com/showthread.php?t=48802

[patlaw]

That circuit board and speaker looks very similar to some Teisco Checkmate amps.

Maybe the Checkmate 66 or 88, they both had tremolo.

Edit;

Here's a CM66 schematic.

[ATTACH=CONFIG]53620[/ATTACH]

[ATTACH=CONFIG]53621[/ATTACH]

Neither is correct. The input is very different. Thanks, though.

[patlaw]

You might try the speaker on another amp to see if the speaker is part of the problem.

Yes, I did that. I believe the speaker is bad, but it is not related to the background noise, which I think is probably a leaky germanium transistor.

[patlaw]

https://music-electronics-forum.com/showthread.php?t=48802

That's the thread mentioned in my first post. Thanks.

[patlaw]

What is a suitable replacement for a 2SB54? Where to get them? Small Bear? I'd love to have a couple to test the circuit to see if what I'm hearing is transistor leakage. I haven't had the problem since I worked on a Vox amp in the seventies.

[patlaw]

I'm almost positive that I found a leaking 2SB54. It's the driver for the phase inverting transformer. After I play the amp for a while, the background noise increases, and the amp's gain drops by 40%. If I spray freeze spray on the transistor, the noise drops and the gain returns.

So, where can I get a replacement for a 2SB54 germanium transistor?

[vintagekiki]

So, where can I get a replacement for a 2SB54 germanium transistor?

https://www.google.com/search?q=replacement+for+a+2SB54

https://english.electronica-pt.com/components-cross-reference?ref=2SB54

https://alltransistors.com/search.php?search=2sb54

http://www.electronicsupplycorp.com/contents/en-us/d61_2SB_Series.html

https://sites.google.com/site/jr2wzq/home/memorandum/germanium_transistor_substitution

[patlaw]

https://www.google.com/search?q=replacement+for+a+2SB54

https://english.electronica-pt.com/components-cross-reference?ref=2SB54

https://alltransistors.com/search.php?search=2sb54

http://www.electronicsupplycorp.com/contents/en-us/d61_2SB_Series.html

https://sites.google.com/site/jr2wzq/home/memorandum/germanium_transistor_substitution

Thanks for the response, but I already know how to do Google searches. The only actual vendor above is Electronics Supply Corp, and they only have one piece.

[galaxiex]

I'm almost positive that I found a leaking 2SB54. It's the driver for the phase inverting transformer. After I play the amp for a while, the background noise increases, and the amp's gain drops by 40%. If I spray freeze spray on the transistor, the noise drops and the gain returns.

So, where can I get a replacement for a 2SB54 germanium transistor?

I dug through my stash of old germs but I don't have that one.

Likely you could sub something from Small Bear, he has quite a few....

There must be one there that would work.

[vintagekiki]

https://electronicparts-outlet.com/en/2sb-series/2741-2sb54.html

https://www.megatrustshop.com/en/product/696

https://www.amsyx.com/2sb54.html

[g1]

I had thought the NTE102A replacement was expensive, but seeing those prices, maybe it's not so bad.

[patlaw]

I had thought the NTE102A replacement was expensive, but seeing those prices, maybe it's not so bad.

They're ALL expensive, especially considering it's the third or fourth Ge transistor I've used in 50 years.