I'm trying to understand why, with the same voltage supplying both plate resistors (100K) and same cathode resistors (1.5k) do I get radically different voltages on the plate (same tube).
With a supply of about 315v to plate resistors, on pin 1 of 12ax7 I have an expected 203v. On pin 6, 305v.
The circuit is a mesa boogie lonestar http://schems.com/manu/mesaboogie/boogie_lonestar.pdf
circuit is the same except that v1-7 has 68k series resistor and relay has been replaced with a jumper so v1-6 goes to both the tonestack and the .005 cap feeding v1-2.
Would this jumper cause the issue?
Thanks Rut
Wrong plate voltage
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Stevem
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Re: Wrong plate voltage
What is your voltage on pins 3 and 8 of that tube as the plate with the lowest voltage should have its cathode reading a higher voltage and that would be due to that section of the tube being in better shape that the other section, so. It may just be that tube, have swapped in others and checked your plate voltage?
In other words the B section of that tube is hardly working.
In other words the B section of that tube is hardly working.
Last edited by Stevem on Mon Sep 08, 2014 3:31 pm, edited 1 time in total.
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Not screaming like the passengers in his car!
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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: Wrong plate voltage
Yes. I should have mentioned that I tried a couple of different tubes. Cathode voltage on the 'good' plate is about 1.2v but around 5v on the other.
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Stevem
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Re: Wrong plate voltage
5 volts is unheard of for the cathode voltage on a ax7!
What voltage is in that tube socket pin with the tube out of it?
What voltage is in that tube socket pin with the tube out of it?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
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!
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: Wrong plate voltage
I'll have to check when I get home this evening. Thanks for your input.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Wrong plate voltage
So has pin 7 lost its 1meg to ground reference?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
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!
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: Wrong plate voltage
Also check the value of the cathode resistor on the "bad" triode.
Re: Wrong plate voltage
It is amazing how 1503 can look like 1501 in bad lighting. Either that or my eyes are growing old. Wrong size on the cathode resistor. Duh!
Thanks for the advice.
Rut
Thanks for the advice.
Rut
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Wrong plate voltage
All fixed up then?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
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!
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!