Varistor Substitute / Varistor Identification

[Paul Marossy]

Is there a way to electronically duplicate what a varistor does?
Or a way to determine the characteristics of a varistor that has zero markings on it?

[R.G.]

Is there a way to electronically duplicate what a varistor does?

Yes.

Or a way to determine the characteristics of a varistor that has zero markings on it?

Maybe.

If the varistor is still OK, you put a current limited variable DC voltage across it and slowly sweep the voltage, monitoring current. This produces a curve of voltage versus current, which equals resistance, and you can then sometimes find varistors that match.

If it's dead, you're stuck with trying to find out from the equipment it's in what it might be by spending days/months/years with a search engine trying to gather snippets of data.

Modern varistors are not like the varistors from, say, the Magnatone amp days. Those varistors had slowly varying resistors versus voltage. Modern ones have much more of a snap action.

If we know what it's in, we may be able to guess at some alternatives. Varistors were after all only components whose incremental resistance varied with the DC voltage across them. Lots of ways to fake that.

[Paul Marossy]

It actually is with respect to the Magnatone amps, need a varistor or equivalent that can do the same thing but not with the snap on / snap off of modern devices.

That being said, you can probably guess what I am wanting to do for my next experiment. 

[R.G.]

There's another way, and it may be what I'm guessing you want to do.

LED/LDRs or univibe style light bulb and LDR. You will probably need to block the DC off the LDRs in the amp.

There was some amp repair guy way back when that had scoured the world and found some subs, but he was trying to sell them like they were platino-gold-plated.

There are other ways too. I dug into this back in the late 1990s. I may have some notes in the archive.

[Paul Marossy]

There's another way, and it may be what I'm guessing you want to do.

LED/LDRs or univibe style light bulb and LDR. You will probably need to block the DC off the LDRs in the amp.

There was some amp repair guy way back when that had scoured the world and found some subs, but he was trying to sell them like they were platino-gold-plated.

There are other ways too. I dug into this back in the late 1990s. I may have some notes in the archive.

Would be interesting to hear anything else you found out about that

[Paul Marossy]

Putting this up here just in case anyone ever has the same question...

I cut one in half. They are some sort of infrared opto couplers, like two infrared LEDs. So no go for what I wanted to use them for.