The Amp Garage

plook

Please indulge my question. I'm trying to be helpful. When you built the amp, did you actually measure 10V? You imply this, but I don't see a clear statement, or I missed it. I ask because 6.2V is clearly not tube selection related and I've started to wonder if the amp has always been like this. If...

plook

Just because you got new tubes is no guarantee there any better then what you took out unless your using high end well tested tubes like apex , Groovetubes or Euro tubes. Even with Groovetubes for example there 1 to 10 numbering system covers a 10% change in output power, and of course that will sh...

plook

About the only thing left to do (and should have suggested this sooner) is measure resistance from pin 3 to chassis. If less than 120Ω replace the cathode capacitor. Thank you. I’ll try that in the morning. Appreciate it. Measured p3 to ground, 121 ohm. I really have no idea what this is. I noticed...

plook

sluckey wrote: ↑Sat Jan 14, 2023 8:52 pm About the only thing left to do (and should have suggested this sooner) is measure resistance from pin 3 to chassis. If less than 120Ω replace the cathode capacitor.

Thank you. I’ll try that in the morning. Appreciate it.

plook

That's crazy. Your plate voltage dropped about 100V which indicates a big increase in plate current. That same current must flow through the cathode resistor, yet you say the cathode voltage is still 6V. Very odd. Maybe your meter is lying to you. That’s a good point. I’ll put a new battery in the ...

plook

That's crazy. Your plate voltage dropped about 100V which indicates a big increase in plate current. That same current must flow through the cathode resistor, yet you say the cathode voltage is still 6V. Very odd. Maybe your meter is lying to you. That’s a good point. I’ll put a new battery in the ...

plook

plook wrote: ↑Sat Jan 14, 2023 5:50 pm No, that is 6v on both pin 3s. Tried different sets of tubes too.

plook

No, that is 6v on both pin 3s

plook

Plate and screen voltage are high along with the low cathode voltage. I’d check the ground connection of the cathode unless you were checking the cathode voltage at a different chassis reference point than the ground lug for the cathodes. Have had a good look, pressed down on the ground with a chop...

plook

sluckey wrote: ↑Sat Jan 14, 2023 1:37 pm Measure voltage on pins 2, 7, and 9 for both EL84s. Looking for six numbers here.

V4 EL84
p2 fluctuates 0.1 to 0.8 MV
P7 424v
P9 420v

V5 EL84
P2 fluctuates 0.1 to 0.5 MV
P7 424v
P9 420v

plook

sluckey wrote: ↑Sat Jan 14, 2023 12:52 pm Weak tubes would be my number one suspect.

That’s what I thought. I put a brand new set in and around the same reading of 6v.

plook

Hi, I made an 18 watt TMB with MV about 10 years ago and gave it to a friend. The voltage measured at cathode resistor 120R and pins 3 of EL84 is 6.24v and should be 10v. What could have caused it to drop and how to fix. My amp work is very intermittent now, big gaps before I come back so my knowled...

plook

I'll do some investigating. I did add a PPIMV to a tweed Pro about 10 years ago and i never liked the tone of that, was too compressed and smooth. It used a double pot i seem to recall. I'll have a good think. Thanks again.

plook

I've noticed that the trem/vib fades to near nothing as i engage the VVR more. Is it lowering the voltage on the trem tube too much? Is there a way to isolate it so normal voltage hits the trem circuit?

plook

Perfect! Thank you so much. At first the on/off/volume didn't have any sound until about 50% turned and the other channel volumes needed to be turned way up, but after a few minutes it all came in to perfection.

I am so grateful for your help and you've made me really happy today.

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