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Old 27th November 2010, 05:32 AM   #1
HP8903B is offline HP8903B  United States
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Default Which tube does my amp use? 12AU7 12BH7 12AX7 6CG7 others?

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Last edited by HP8903B; 5th September 2013 at 07:35 AM.
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Old 27th November 2010, 05:37 AM   #2
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What kind of amp is it?
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Old 27th November 2010, 05:38 AM   #3
6L6 is offline 6L6  United States
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Please give us more info.

Is this a commercial amp?

Is it home built?

Why are the tubes out of it?

Where did you get it?

Do you have any information at all about the amp?

Can you take more/better pictures of it?

Can you take a picture of the insides where the small tubes connect?
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Old 27th November 2010, 05:39 AM   #4
HP8903B is offline HP8903B  United States
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It is a DIY amp that I bought that came with no tubes. All the tube sockets are not labeled.
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Old 27th November 2010, 05:47 AM   #5
HP8903B is offline HP8903B  United States
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I don't have any information on the amp.

I attached pictures of the inside.

I met up with SY and he looked at the amp for me. He said that the front tube is 12AU7 or 12AT7. The middle and back tubes are 6CG7. But as I mentioned, The middle socket will not light up the 6CG7.
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Old 27th November 2010, 05:50 AM   #6
HP8903B is offline HP8903B  United States
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Middle picture is of the back socket.
Right picture is of middle socket.
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Last edited by HP8903B; 27th November 2010 at 05:54 AM.
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Old 27th November 2010, 05:51 AM   #7
HP8903B is offline HP8903B  United States
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Front socket picture
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Old 27th November 2010, 06:00 AM   #8
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Are you sure the 6CG7 you have is good?

Last edited by astouffer; 27th November 2010 at 06:02 AM. Reason: typo
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Old 27th November 2010, 06:05 AM   #9
HP8903B is offline HP8903B  United States
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Yes I am sure. I have many 6CG7.
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Old 27th November 2010, 06:28 AM   #10
HP8903B is offline HP8903B  United States
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I got the following measurement from the 3 small tube sockets:

Front: Plate is 420 VDC, Grid is unknown, heater is 7 VAC

Middle: Plate is 948 VDC (that is right), grid is 420 VDC heater is 7 VAC.

Back: Plate is 443 VDC, Grid is unknown, One heater is 7 VAC and the other is around 3 VAC.

The two wires going to the grid of both power tube is coming from the back small socket.
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