Which tube does my amp use? 12AU7 12BH7 12AX7 6CG7 others? - diyAudio
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Old 27th November 2010, 04:59 AM   #1
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Join Date: Jun 2010
Default Which tube does my amp use? 12AU7 12BH7 12AX7 6CG7 others?

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

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

The middle and front sockets only 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.
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Last edited by HP8903B; 27th November 2010 at 05:25 AM.
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