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Jimmy Rocket · May 3rd, 2012, 08:45 AM

Ok, I popped the hood this morning and here's what I found...

I had already installed a 1M grid stopper on pin 7 of v4 so not the issue I guess.

Most pin voltages were right on target but pins 1 and 3 of v4 were a little low (211v and 2.1v respectively).

Pins 1/6 of v2 were below 400v at 383v

While I was in there I re- routed the anode wire of v3 so that I could bundle the anode/grid/cathode wires for that triode. I also collected these leads on each of the other pins. I re-flowed some solder on a few joints to be sure and I checked the bias.

Here's the interesting bit. The bias was set way low at 15-16 mA. The power tubes are getting 410 volts so it seems like the bias should at least be 21 mA to be in range. I upped the bias to those tubes so that they were getting 21.5 mA and 22.3 mA and I buttoned her back up.

To my ears the sound I was talking about has disappeared. I wonder if I was getting some crossover distortion because the tubes were so cold?

I can still hear that the speaker isn't quite giving me everything I need and that there is a slight buzz from the speaker, but it sounds mechanical and not electronic. I'm thinking about going with a 50watt weber or a ragin Cajun so that I can Let the cleaner side of this amp shine. Any recommendations?

I'll run it some more and report back.

May 3rd, 2012, 08:45 AM	#12 (permalink)
Jimmy Rocket Tele-Holic Join Date: Nov 2010 Location: Durham, NC Posts: 579	Ok, I popped the hood this morning and here's what I found... I had already installed a 1M grid stopper on pin 7 of v4 so not the issue I guess. Most pin voltages were right on target but pins 1 and 3 of v4 were a little low (211v and 2.1v respectively). Pins 1/6 of v2 were below 400v at 383v While I was in there I re- routed the anode wire of v3 so that I could bundle the anode/grid/cathode wires for that triode. I also collected these leads on each of the other pins. I re-flowed some solder on a few joints to be sure and I checked the bias. Here's the interesting bit. The bias was set way low at 15-16 mA. The power tubes are getting 410 volts so it seems like the bias should at least be 21 mA to be in range. I upped the bias to those tubes so that they were getting 21.5 mA and 22.3 mA and I buttoned her back up. To my ears the sound I was talking about has disappeared. I wonder if I was getting some crossover distortion because the tubes were so cold? I can still hear that the speaker isn't quite giving me everything I need and that there is a slight buzz from the speaker, but it sounds mechanical and not electronic. I'm thinking about going with a 50watt weber or a ragin Cajun so that I can Let the cleaner side of this amp shine. Any recommendations? I'll run it some more and report back.