Which tube does my amp use? 12AU7 12BH7 12AX7 6CG7 others?

manp111 · 27th November 2010, 05:32 AM

Could some one tell me how I can figure out which small tubes my amp uses?

The back socket near the transformers lights up the 6CG7 but not the 12AX7 or 12AU7.

The middle and front sockets light up 12AX7 or 12AU7 but not the 6CG7

I am pretty sure that the amp uses 845 power tubes.
Without ANY tube installed, the power tube grid is -350 DCV. With the 6CG7 in the back small socket, the power tube grid is +145 VDC. With the 12AU7 on the middle and the front socket, the power tube grid is -45 VDC. It has adjustable bias.

I only tried the tubes mentioned because those are what I have.

SGregory · 27th November 2010, 05:37 AM

What kind of amp is it?

6L6 · 27th November 2010, 05:38 AM

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?

manp111 · 27th November 2010, 05:39 AM

It is a DIY amp that I bought that came with no tubes. All the tube sockets are not labeled.

manp111 · 27th November 2010, 05:47 AM

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.

manp111 · 05:54 AM

Middle picture is of the back socket.
Right picture is of middle socket.

manp111 · 27th November 2010, 05:51 AM

Front socket picture

astouffer · 06:02 AM

Are you sure the 6CG7 you have is good?

manp111 · 27th November 2010, 06:05 AM

Yes I am sure. I have many 6CG7.

manp111 · 27th November 2010, 06:28 AM

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.

27th November 2010, 05:37 AM	#2
SGregory Tubie Noobie diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	What kind of amp is it? __________________ Living Life Doing the Waltz in 4/4 meter.

27th November 2010, 06:00 AM	#8
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	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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27th November 2010, 05:38 AM	#3
6L6 diyAudio Member Join Date: Oct 2010 Location: Denver, Colorado	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?

27th November 2010, 05:39 AM	#4
manp111 diyAudio Member Join Date: Jun 2010 Location: Austin, Texas	It is a DIY amp that I bought that came with no tubes. All the tube sockets are not labeled.

27th November 2010, 05:47 AM	#5
manp111 diyAudio Member Join Date: Jun 2010 Location: Austin, Texas	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.

27th November 2010, 06:05 AM	#9
manp111 diyAudio Member Join Date: Jun 2010 Location: Austin, Texas	Yes I am sure. I have many 6CG7.

27th November 2010, 06:28 AM	#10
manp111 diyAudio Member Join Date: Jun 2010 Location: Austin, Texas	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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