2A3 SE Problem

mark02131 · 20th February 2010, 12:53 AM

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

JohnAtwood · 20th February 2010, 01:51 AM

If the problem moves with the tube, it is almost for sure a weak tube. Do you have any other output tubes to try or can you test your tubes on a tube tester? I am assuming both output tubes are the same type.

- John Atwood

mark02131 · 20th February 2010, 02:09 AM

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 · 07:31 AM

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?

JPeitzman · 20th February 2010, 07:46 AM

I could swear that my TC-1 has configurations for 2A3's. Alas it is down stairs and I am warm and comfy in bed. If you don't mind giving me until morning I can check it out for you then. I just cannot remember off hand.

mark02131 · 20th February 2010, 12:11 PM

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.

JPeitzman · 20th February 2010, 03:28 PM

Heathkit TC-1 2A3 Configuration:
Type - 3
Filament - 2.5
Plate - 28
Top - BC
Bottom - D

Yeah my scroll paper is probably in about the same condition, something I too have been meaning to fix. Hopefully this helps!

mark02131 · 20th February 2010, 06:14 PM

Thanks JPeitzman

I tested the tubes and the one was bad. Thanks everyone !

20th February 2010, 12:53 AM	#1
mark02131 diyAudio Member Join Date: Nov 2005 Location: Boston, MA	2A3 SE Problem 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

20th February 2010, 01:51 AM	#2
JohnAtwood diyAudio Member Join Date: May 2006 Location: Rural Nevada	One channel weak If the problem moves with the tube, it is almost for sure a weak tube. Do you have any other output tubes to try or can you test your tubes on a tube tester? I am assuming both output tubes are the same type. - John Atwood

20th February 2010, 07:28 AM	#4
azazello diyAudio Member Join Date: Aug 2008 Location: Bulgaria	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? Last edited by azazello; 20th February 2010 at 07:31 AM.

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20th February 2010, 02:09 AM	#3
mark02131 diyAudio Member Join Date: Nov 2005 Location: Boston, MA	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.

20th February 2010, 07:46 AM	#5
JPeitzman diyAudio Member Join Date: Jan 2007 Location: Iowa	I could swear that my TC-1 has configurations for 2A3's. Alas it is down stairs and I am warm and comfy in bed. If you don't mind giving me until morning I can check it out for you then. I just cannot remember off hand.

20th February 2010, 12:11 PM	#6
mark02131 diyAudio Member Join Date: Nov 2005 Location: Boston, MA	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.

20th February 2010, 03:28 PM	#7
JPeitzman diyAudio Member Join Date: Jan 2007 Location: Iowa	Heathkit TC-1 2A3 Configuration: Type - 3 Filament - 2.5 Plate - 28 Top - BC Bottom - D Yeah my scroll paper is probably in about the same condition, something I too have been meaning to fix. Hopefully this helps!

20th February 2010, 06:14 PM	#8
mark02131 diyAudio Member Join Date: Nov 2005 Location: Boston, MA	Thanks JPeitzman I tested the tubes and the one was bad. Thanks everyone !

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