Tube Amp Archive

I'm not clear if you have the 330k and 220k paralleled acros the 100k dropping resistor now. In any case, does it sound better now at any pot setting than it did with the 330k alone? Keep the configuration you like best. If it's the one with all three resistors paralleled in the power supply string...

I'm curious about your reported AC voltage at the rectifier. Do a little something to satisfy my curiosity? Set the meter to VAC, put the probes in a wall socket and tell me if you get around 120VAC. I get 121VAC at the outlet. You want to know what's next? I think you should let your ears decide w...

Martin/Phil: New voltages with the 220K resistor in place and there were some slight changes in the numbers: V1 Pin 1 - 183VDC (166VDC) Pin 2 - 0.1mV (-10.0mV) Pin 3 - 1.84VDC (1.65VDC) Pin 6 - 148VDC (136VDC) Pin 7 - 0.0mV (0.0mV) Pin 8 - 1.30VDC (1.21VDC) V2 Pin 2 - 13mV (16mV) Pin 3 - 8.0VDC (8.0...

Great! Sounds like you're having som fun with this. I'd try adding the 220k to what you have now to get another 20k or so off of the power string dropping resistance (put it on the terminal strip lugs maybe) and see what change that makes for better or for worse. You need a third data point to dete...

Martin/Phil: I got to playing around with the current setup, 320K resistor tacked to 100K, and initially I got a good tone from the guitar at 22K, the pot, but a warbly tremolo and a lot of hum. So, I reconnected the pot leads directly on the lugs versus on the resistor leads and that addressed the ...

I will recheck the voltages in the morning as I am at work right now. I probably measured them incorrectly. When you say the trem is working like it was earlier, do you mean the funky whump-whump or do you mean it's better now? If there is some hum in the signal path, then the trem will modulate tha...

Either texstrat is measuring it wrong or there is a short from the HT secondary to the filter caps, bypassing the rectifier. I'm open to other suggestions to explain this. That's what I can come up with. Ground to chassis and positive probe to each lead coming out of the capacitor on the positive e...

Martin/Phil: Here are the results using a 50K pot and starting with a 330K resistor tacked onto the 100K resistor between green and blue ps cap leads. Here are the new voltages, values in parenthesis were yesterdays numbers. V1 Pin 1 - 186VDC (186VDC) Pin 2 - 0.0 (0.0mV) Pin 3 - 2.09VDC (2.20VDC) Pi...

Remove the 820R. Wire the pot as a variable resistor. Jumper the wiper with one outer leg. Then use the other outer leg and the wiper (middle lug). This on the cathode, so your typical 1/2W pot will work fine. So if I understand this correctly, the wiper, middle lug, two leads will come off it, one...

So now you have a baseline using the original circuit values, and it leaves a little to be desired. Probably the 4k7 cathode resistor needs to be smaller, but that will drop the supply voltage below 200V as you saw when the 820R resistor was across it. I guess it worked, but the plate voltage on th...

I would be in for one of the kit, with the chassis punched. This has been a very interesting thread to read.

Yes. I like these voltages better. Can you elaborate on how the tremolo sounds? What happens as you rotate the pot? How's the tone of the amp, in general?

Phil it has more of a whump, whump loose bassy sound. Before it was tighter and had more treble to it.

Ok, I desoldered the 820R resistor and I still have sound. The tremolo sounds real funky, but the voltages look a bit better. Whereas before, the amp was stone quiet, no hum/hiss, now I have a small amount of hum/hiss. Here are the new voltages, values in parenthesis were yesterdays numbers. V1 Pin ...

Guys, had to work last night. I did not de-solder the positive lead on the ps caps when I tested them. The caps were in circuit and power was on. Also, the voltages that I listed are where it settled, meaning I got voltages in the 125+ range, and then it steadily decreased until the voltage drop sto...

Yes, it seems wrong, but I thought we need to concentrate on the ripple at node 1 before looking downstream. Now that you raise it, maybe the OP isn't measuring it correctly? What else might explain this? This is hard from far away. Texstrat, you are taking these measurements with the black probe g...