Originally posted by Enzo
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When someone buys a used amp, who knows what state the thing is in? The 1st thing you need to do, for a tube amp, is check the tubes.
I had a guy come in with a DSL 50, limited edition Orange Crunch. Beautiful amp. He wanted to make sure it was biased right but the amp sounded thinner than my DSL (I a/b's the amps and he could not believe the difference) and had low volume. He bought it that way and didn't know any better. Sure enough, V1 was weak as shown on the tester. I gave him a used tube I had lying around and he left with a huge grin on his face.
The old Eico 667/666 are decent but you need to know how to interpret the charts. They're pretty robust and can be calibrated easily. A favorite of mine is the B&K 707. The switch bank can be iffy so a good and thorough cleaning is a must. They're also pretty easy to clean out.
If the panel meters are not working right, you can replace them with a digital readout (like I did on the Eico). On the B&K, I added a voltmeter out so I can get a good reading.
I regularly test preamp and power tubes on it. Weed out the bad ones and gives you and customers a vote of confidence in the tubes that are installed in the amp. Of course, there are visual clues when examining a tube and the ultimate test is in the amp in terms of noise, bias stability, microphonics, etc.
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