Looking for odd diodes!

[Bill Moore]

I recently recieved a Music Man RD 100 amplifier that was dead. I rebuilt the HV, and LV power supplies, but still had a problem when attempting to power up. Seems that this design uses some high voltage diodes in the primary OT circuit, and 1 was shorted. I removed to bad one, and the amp sounds great. I had tried to find these diodes when I was locating other parts to get the amp up again, but had no luck.
The original # is MR 250-5, and someone at the MM forum listed 1N1734A as a substitute part. The diode is rated 5KV, 250ma.
Any ideas?

[The Dude]

The 1n1734A should work. You could also stack diodes like some of the old Ampegs did to get up to the voltage rating you want. I would recommend that you replace both with the same arrangement to keep everything matched (unless you can find and exact replacement).

[Enzo]

We call them flyback diodes. They are there to prevent the output transformer from being destroyed if you play the amp without a speaker. So they are like seatbelts in your car: They are not necessary to its operation, but they are an important safety element.

Many modern amps have them, and you could use most anything.

Peavey uses SR2373, their part number 70402873

AMpeg SVT uses three 1N4007 in series

Fender uses R3000, their part number 029690001

[Bill Moore]

Thank you all! Do you think 3KV will be sufficient, the original is rated for 5KV. Another fellow recommended the 1N4007 avalanche stack.
I doubt at the volume levels I play that I would ever be able to blow that EV 15's voice coil anyway.

[The Dude]

I would think 3KV would be plenty sufficient and 3 stacked 1n4007's is what most guys use when repairing the Ampegs. Again, I would replace both sides with the same "array".

[Enzo]

They all do the same job in their respective amps. Pick a method. They are equivalent.

You may never blow your EV speaker, but that doesn't mean you will never trip over your speaker cord and pull it half out, or have a bad speaker cord, or forget to plug a speaker in, etc etc etc.