Bill Epstein Messages: 1088 Registered: May 2009 Location: Smoky Mts. USA
Illuminati (2nd Degree)
Fried a resistor on the driver stage of the 45 amp the other day. Bad driver tube took it out. Or bad CCS mosfet took out the tube, or... Have had a problem with the turn-on surge of the B+. Even damaged the other channels mosfet. In looking over the problem and replacing the bad parts at the WSOTT meeting Saturday, Steve suggested implementing a switch on the B+. With a .01uF 2kV cap across the terminals. Last night I installed it. On the center tap connection to ground. Just a SPST 250 VAC, 10 amp rated toggle. Powered up and let the filaments warm up for a few minutes, then closed the switch. No flashes or crackles, which I had previously.
That's a great approach and it's a good reason to get hold of some of those books, like the Radio Amature's Handbook (especially older ones). The only drawback here is that you'd have to have seperate filiment transformers. Probably not a big deal, but can be an unplanned addition to the chassis. I recently found, by the way, that Hammond makes some nice fil transformers with dual secondaries - for example, two x 2.5v windings (266M5). This makes it so you'd need fewer seperate fil tfr under the hood.
It's after Christmas...is the amp done? Any fireworks? did it work the first time( if it did, you have got great skill! )? Got the 6W6 mod done? How does it sound?
WOW there buddy, you sure are pushy for an answer! The 300B thing was a bust. The Tamura 2.5v-5v transformer did not have enough cahuna's to drive the 2A3's let alone the 300B's. I put the original Hammond 166L2's I bought in and it worked right out of the box as a 2A3. After some resistor tweaking and replacing the 6SL7 drivers with 6EM7's, the darn thing REALLY sounds nice! It isn't as good as my friends $5k P-25 amp but still very musical. As far as my skillset, if it wasn't for the help of a close friend, they probably would have found my charred, half parakeet-eaten body in the condo after the spring thaw. I really appreciated his patience, help, and insight with my project. I returned the favor by preventing his electrocution.
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