I recapped a 70s Bassman 100 (also new diodes and screen resistors). Voltages all look good, and I'm biased at about 65%, but I'm getting only about 30 watts output. Signal going into the PI is strong, but on the output of the PI, I don't understand this distortion.
In the scope photo, on left side is output of both legs of PI with master volume at 4. On right is master volume dimed (scale changed to make waves similar in height). What does this triangle distortion mean?
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Triangle wave distortion Bassman 100 - solved: slew rate dis
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Triangle wave distortion Bassman 100 - solved: slew rate dis
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Last edited by xtian on Tue Feb 10, 2015 6:33 pm, edited 1 time in total.
I build and repair tube amps. http://amps.monkeymatic.com
Re: Triangle wave distortion Bassman 100 - solved: slew rate dis
I'll tell you why! Slew rate distortion! (Don't you love Google?) I had my signal generator set at 10KHz, not 1KHz. Duh. Now I'm seeing about 95 watts clean output power.
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You have to be idiotic in order to feel smart when you cure your idiocy.
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Stevem
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Re: Triangle wave distortion Bassman 100 - solved: slew rate dis
What where you testing previously that you had the scope set to read up at 10k?
I guess one clue if your where running into a resistive test load would have been not hearing any 1K tone ringing out of the OT.
None the less, only 30 watts at 10k, does the amp still have the 70s anti osccilation caps in place on the output tubes?
In regards to the saw tooth, what does the input side of the PI look like with the amp dimed, and what signal level are you driving the amp with?
Also how much does the B+ voltage on the PI drop off to with the amp pumping out its max rms output power and also at peak power?
I guess one clue if your where running into a resistive test load would have been not hearing any 1K tone ringing out of the OT.
None the less, only 30 watts at 10k, does the amp still have the 70s anti osccilation caps in place on the output tubes?
In regards to the saw tooth, what does the input side of the PI look like with the amp dimed, and what signal level are you driving the amp with?
Also how much does the B+ voltage on the PI drop off to with the amp pumping out its max rms output power and also at peak power?
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Triangle wave distortion Bassman 100 - solved: slew rate dis
Hey, Steve. I was testing a crossover network earlier. And yes, I did notice I wasn't hearing the tone, but that clue didn't penetrate.
Yes, the snubbers are still on the plates of the power tubes. The input of the PI looked good, and did not distort at 10KHz. Didn't measure voltage drop during the audio test.
Amp is back in the hands of owner. I had a chance to play it loud first. Just, wow. Ballsy is an understatement--it ripped mine off. Now I have to order new ones. Mouser?
Yes, the snubbers are still on the plates of the power tubes. The input of the PI looked good, and did not distort at 10KHz. Didn't measure voltage drop during the audio test.
Amp is back in the hands of owner. I had a chance to play it loud first. Just, wow. Ballsy is an understatement--it ripped mine off. Now I have to order new ones. Mouser?
I build and repair tube amps. http://amps.monkeymatic.com