70's Vibrolux Ugly distortion

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abelljo
Posts: 24
Joined: Wed May 16, 2012 1:35 am

Re: 70's Vibrolux Ugly distortion

Post by abelljo »

martin manning wrote:Hold on, pin 6 on the PI tube should be pretty close to pin 1 (within a few volts). That triode (pins 6, 7, and 8) is not conducting. You're seeing the supply voltage at the socket (I assume that's where you measured) so check the socket contact with the plate and cathode pins.

And, the tube is good right? Fix this and I think you've got it.
Wow, I wonder if a measured something wrong or I missed it completely. I'll look and if I confirm the voltage is way off I'll change the 100k resistor. I'll try the .1 cap too if I don't see a change. The tube is good I swapped them all as part of the troubleshooting.

Thanks!'
abelljo
Posts: 24
Joined: Wed May 16, 2012 1:35 am

Re: 70's Vibrolux Ugly distortion

Post by abelljo »

martin manning wrote:Hold on, pin 6 on the PI tube should be pretty close to pin 1 (within a few volts). That triode (pins 6, 7, and 8) is not conducting. You're seeing the supply voltage at the socket (I assume that's where you measured) so check the socket contact with the plate and cathode pins.

And, the tube is good right? Fix this and I think you've got it.
Martin, you got it. the .1 cap was bad. Replaced it and now the amp sounds loud strong and beautiful!

PROBLEM SOLVED

Thanks for the fresh set of eyes and knowledge.
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martin manning
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Re: 70's Vibrolux Ugly distortion

Post by martin manning »

I should have zeroed in on that cap being shorted as a possible explanation for the high voltage, but you're welcome, and it's great to hear you got it going!
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