Will Fender LDR Optocoupler Work in Magnatone Amp?

[christill1]

Hello! First time poster here. I've got a sweet mid-'60s Magnatone MP-1 guitar amp. My awesome repair guy (Russ Shaw) needs an LDR optocoupler for it. He don't use the 'Net so has asked me to find one. His question is, really, will a Fender LDR optocoupler work in the Magnatone? I see the LDR optcouplers for Fender amps on Ebay. Will one of those work? Many thanks, Chris Till

[Jazz P Bass]

From what I can gather the MP-1 uses the TM-1 tremelo optocoupler, like in the Ampeg Gemini I.
Fliptops has them.

Here is a link to the MP-1 info page.: MagnatoneAmps.com

[christill1]

Many thanks for the tip!

[TimmyP1955]

You might see if the new Magnatone folks can be of any help in that regard. (3 one 4) six 69-Nine 810

[christill1]

Hey, I'm back! Well... the Ampeg optocoupler did not work in the Magnatone. It was too big, would not mount, etc. In the meanwhile, I had Mercury Magnetics fabricate a new reverb transformer for it. I will call Magnatone to see if someone there can help. Meanwhile, if anyone has a suggestion for locating a optocoupler for a mid-'60s MP-1, I would be very appreciative. Chris Till 937-767-2326

[Jazz P Bass]

Well, here is the schematic.

They even list the optocoupler lamp#: 1869D.

The circuit also uses a NE2H neon lamp for the oscillation circuit.

So maybe your tech missed the fact that it is not even oscillating.

magnatone_mp1.pdf

[Tom Phillips]

... the Ampeg optocoupler did not work in the Magnatone. It was too big, would not mount, etc. ...

If it's just a mounting problem maybe re-configuration of the bulb and the LDR would solve the problem. Can you post some photos? That would really help. Show the old part and the replacement part that didn't fit and amp gut shots.

I'm also perplexed that your repair guy originally asked if a Fender unit would work. When you look at the schematics comparing the Fender circuit to the MP-1 circuit it should be clear that the Fender uses a neon bulb in the light bug and the MP-1 uses an incandescent bulb. Maybe he was confused because there is also a neon bulb in the MP-1 that is separate from the tremolo light bug. The NE-2 bulb in the MP-1 is part of a relaxation oscillator circuit. Do you have the schematic?

Edit: Ha... simultaneous typing. Glad we are on the same page.

[christill1]

JPB,
Thanks for input and schematic. That's the schematic from Weber's "A Desktop Reference of Hip Vintage Guitar Amps," which is the same one he is working from. His problem is that he isn't a surfer-of-web. My problem is that I'm not super-literate on tube amps. (I love 'em and am learning, but I am worthless in fixing them.) So, I will give him this info and we'll see.
Thanks, Chris

[christill1]

We do have the schematic. I will get print out your answers, give them to him, and take pictures of guts. Many thanks, Chris Till