• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

2A3 SE Problem

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mark02131

mark02131

Member
Joined 2005
I built a 2A3/45 amp and one tube seems to have 1/2 the output of the other. I'm not sure if it's the tube or the amp.

I checked the Anode voltage and it's 310 on both tubes but when I looked at the Cathode voltage, One is 38v, (close to the 45v that I should see) but the other is only 22v? I checked the value of the 750 ohm cathode resisters and they are both 749.

If I move the tube from one channel to the other the voltages follow the tube. Any idea's Is it the tube or something I I may be doing wrong. -- Thanks
 
mark02131

mark02131

Member
Joined 2005
There were a matched pair and I don't have another pair or tube to try. My Heathkit tc-1 tube tester does not show a 2A3 on the config so I can't test the tubes, I have a 45 pair coming but don't have them yet. I am thinking it may be a week tube but thought I should check to make sure I didn't miss something.
 
azazello

azazello

Member
Joined 2008
38v/750 = 51 ma - good emission /this is normal mode/.
22v/750 = 29 ma - bad emission.
Maybe Your ampl. will work good after 2-3 days work? And emission second tube will increase....
Or You can try put in cathode 500 ohm for a few hours to increase emission?
 
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mark02131

mark02131

Member
Joined 2005
JPeitzman:
If you have the config for the 2A3 that would be great

My Heathkit TC-1 scroll paper will not scroll that low, I need to fix it but it's so old I don't want to break the paper. If you have the config for the 2A3 that would be great.

Azazello:
Thanks. I will run it today again for a while just to see if it improves. I think I will also get another tube also.
 
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