Transistor for Marshall 1987T tremolo?

[øøøøøøø]

I know we have some people here who are more "Marshall amp subject matter experts" than I am.

I have a 1961 Bluesbreaker from about 1970... same circuit as the 1987T, just in a 4x10 combo configuration.

Tremolo is not working. Schematic specifies a 2G374 transistor (Germanium).

That's a tricky part to find... anyone know a good substitute? I suspect the leaky nature of the Ge might be important here (to create a tremolo instead of a repeat-percussion effect from the switching action).

Any thoughts for a substitute part? OC44 maybe?

Cheers!

[ryland]

I would certainly try an OC44 as a replacement, really any PNP GE should work as long as it's not too leaky and has a useful gain. You may have to audition a few to get a good one.

Are you sure that the transistor is at fault? I'm not saying that it isn't, but I'd be more suspicious of other components drifting over time and heat exposure.

[øøøøøøø]

I’m not sure yet; I’ll dig into this one soon for a more detailed diagnosis. I have ruled out the tube, and assumed the semiconductor device would be a more likely candidate for failure than the passive components, but I haven’t verified anything

[Sweetfinger]

When a trem isn't oscillating in an old amp, I suspect the caps but an old Ge transistor should get some scrutiny. If you can find specs on the original, that will help sorting a replacement.

[Dr Tony Balls]

I would certainly try an OC44 as a replacement, really any PNP GE should work as long as it's not too leaky and has a useful gain. You may have to audition a few to get a good one.

I agree with this assessment. PNP in the 70-120 gain range ought to do it. Might not even need to be germanium, but couldnt hurt.

[OffYourFace]

I'd try to find a modern replacement unless you plan to sell the amp. From what I can recall, the tremolo is pretty mild/boring in these?
It would be cool to have a stronger tremolo in it. I for one would like a "repeat-percussion effect" in a Marshall

But I know how you are I would look at replacement parts for old organs from the same era... like Italian & German made stuff.

[cbrown]

https://www.radiomuseum.org/tubes/tube_2g374.html
This site lists the AC126 and OC75 as possible alternatives, both are currently available on ebay.

https://alltransistors.com/crsearch.php ... 2=0&r1r2=0
Some other possibilities listed here.

The OC44 has a max cb voltage of 12V compared with the 2G374's 25V, don't know if this would be a problem, depend on the voltage at that point in the circuit.

Hope you get it working again.