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Post by johneppstein on Oct 13, 2021 13:58:15 GMT -6
Which circuit is it? If it has the master volume with pull distortion then meh. A circuit like nothing you ever imagined, at least once you're out of the preamp. I forget what they actually use for the PI tube, but it doesn't drive the outputs. There's a 6l6 or 6v6 (forgot again) driver tube in the way. Tubes are specially selected GE 6550s, USE NO OTHER TUBE or you'll have to detune the amp to prevent blowing up. There are 3 power amps, one pair of outputs per amp. Each amp puts out around 150 watts into its 8ohm 18" gauss folded horn cab. Did I mention that it was marketed as a bass amp, despite the presence of tremolo and reverb?
The manual for changing tube and biasing is a small book - 30 steps to the bias procedure - for each power amp. You had to pass a test to work on them.
A couple or so years later they came out with a detuned version, the 300PS.
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Post by johneppstein on Oct 13, 2021 14:10:01 GMT -6
Which circuit is it? If it has the master volume with pull distortion then meh. Had one. Failed attempt at modernizing or modifying an amp (for overdrive) that was designed to be the pinnacle of clean. Sold it. Well starting by rebuilding to (more or less) Brownface spec would be a start. |
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Post by EmRR on Oct 13, 2021 16:23:26 GMT -6
I had one of those 400's on the bench once, after it had been on a bunch of other benches. You could bias it up with new tubes and it would run for a couple hours, then cease. I heard it got parted out eventually.
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Post by johneppstein on Oct 19, 2021 12:17:56 GMT -6
I had one of those 400's on the bench once, after it had been on a bunch of other benches. You could bias it up with new tubes and it would run for a couple hours, then cease. I heard it got parted out eventually. Did you go by the factory manual for the bias? Because if you don't the amps will not be stable - THEY TELL YOU THIS! People who are aware of this and ignore it are idiots. (I'm assuming that this doesn't include you?) You also MUST use the correrct GE6550 tubes, which are rarer than hen's teeth now.
It';s a 30 step process for each of the 3 power amps.
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