mad dog said:
Cap: Varistors seldom go bad. Those 7189A tubes are expensive ... maggies are coming up in value. No doubt due to idiots like me who talk about them all the time. ... Ampegs have yet to make the leap. It's pretty astonishing, how much amp and tone you can get on the cheaps in Ampeg land. Most players truly could care less.
Hi Michael; Again, congrats on the Ampeg and, unless I forget to say it: "Long live your (and default's) Maggies". At your suggestion, I signed on over on the Magnatone site; that's the real CJ over there btw and hung around long enough to read all the: "What's a varistor?", "Who makes them?", "Where can I buy them?", "How do I know which ones go in my amp?" and a few of CJ's replies. I also reseached several Maggie schematics and geeked around at Mouser / Allied / DigiKey / Newark / Ocean State and a few Google-driven others.
When I was in 5th grade, my friend Tommy Burke and I used to fill a test tube with vinegar and baking soda, gently put cork in the end, and toss the test tube back and forth - a variant of Russian Test Tube Roulette - until one of us got wet. Most electronic parts are rated for a specific characteristic; voltage/amperage handling, resistance ...whatever and under normal use, all / nearly all passive amp components fail due to heat, repeated exposure to current and voltage, and/or lack of operator anality. If the varistor does what I think it does; conduct / open / conduct at nearly 60 hz, then it's a busy thing for sure.
Without knocking myself out, I didn't see any way to determine which of the several varistors that were out there would work in any of the designs I looked at. For the sake of this, I'm willing to assume that varistors rarely fail but ... let's say one or more does. The very function that makes Maggie' unique, as I understand it, would be disabled and the only fix-em-'up in plain view would be to buy 3, 5, 9 or so of several available types and then, by trial and error, put-em-in-take-em-out until it was working. I'd hate to buy a Maggie from Tommy Burke only to have it explode/fail at my house.
Q: "What's that?"
A: "My new-to-me Maggie"
Q: "Cool, does it work?"
A: "Not really, wanna beer?"
In fairness to CJ and the other Maggites and in part due to the format of that Forum, I didn't find a solution to a broken varistor. Like I said, long live yours and default's but I'm not gonna mess with one 'til I know there's a way to fix the very thing that makes them extraordinary. At the risk of putting too fine a point on it, the Gibson GA4RE in my siggie is also a piece of vintage, but non-working, 60s design. The 'Oil Can' tone is gone and, without buying and cannibalizing two or three dead units .... like some Maggie rebuilders do ... it ain't comin' back .... to say nothing of $40/ea for non-descript 7189s and $100/ea for Mullards.
My plan for the GA4RE is to convert it to a tube preamp and/or reverb unit; we'll see. In the meantime, I have my eye on an Ampeg GII like yours; question to seller re/ 7591 or 6L6; also appropriately tatted... :wink:
Best regards,
John