Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by TimmyP, Apr 8, 2015.
Had a BFSR with a very asymmetrical output. The 82k in the PI had drifted up to 133k!
Yeah, easy to overlook some. I've ran into some really high ones lately too. 100k running 130+!
You can check the value of most every resistor in any tube amp with it turned off. If you know your resistor colour codes you can check any amp in about 5 minutes.
Someone told me cracked carbon resistors absorb moisture over the years and erode inside. I have no idea if this is true, but like you say they can drift up a LOT in value.
Donny I'm dammed near in Canada so the winters are long and dry. What's that have to do with carbon comps? Well I rarely see the the problems with moisture like every body talks about with them.
Talking with a couple of guys about it one from New England and one from Texas the guy in Texas saw more noisy carbon comps than us Yankees.
As far as mesuring resisters I recap the amp and service it first then see how it sounds. If it sounds good I stop right there. Yeah they drift and were 10% to start with. You start matching the schematic and you'll be replacing everthing inside a 50 year old amp and have some real pissed of customers.
After all they're musical instruments not precision test equipment.
That said if it's broke you have to fix it.