Totally beginner magnavox 8608

To use a 12AX7, one heater wire goes to pin 4 and 5, the other goes to pin 9. The 6bq5 heater wires are on pins 4 and 5. I would connect 4-5 on the 12ax7 to pin 4 on the 6bq5, and pin 9 on the 12ax7 to pin 5 on the 6bq5.
Ok i think I understand what I did wrong, but just to be clear between the pin 4and5 I just solder a wire and then I solder another (existing one) from pin 4 of 6bq5 to either one of 4 or 5?
 
Ok i think I understand what I did wrong, but just to be clear between the pin 4and5 I just solder a wire and then I solder another (existing one) from pin 4 of 6bq5 to either one of 4 or 5?
Yes, the heater wire coming from pin 4 of the 6BQ5 goes to pins 4 and 5 of the 12AX7. The heater wire coming from pin 5 of the 6BQ5 goes to pin 9 of the 12AX7.

Double check the other connections to the 12AX7 to make sure it isn't wired like a 6EU7. I've attached the pinout diagrams.
 

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  • Pinouts 6EU7 and 12AX7.pdf
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Yes, the heater wire coming from pin 4 of the 6BQ5 goes to pins 4 and 5 of the 12AX7. The heater wire coming from pin 5 of the 6BQ5 goes to pin 9 of the 12AX7.

Double check the other connections to the 12AX7 to make sure it isn't wired like a 6EU7.
Thanks a lot. Will check once at home and keep you posted.
 
See my edited post above with the pinouts of the two tubes.

Going with a 12AX7 does give you more options if you want to try different brands or some of the new production versions.

If you're going beyond a simple change from 6EU7 to 12AX7 you should remember that the changes Dave made are based on his decision to replace the output transformers. That decision was made because the stock output transformers were designed for use with 4 ohm speakers and he found that they performed very poorly when more common 8 ohm speakers were used. If you decide to keep the stock transformers some of those other changes may not be appropriate. You might want to ask about that on his mod thread. If you decide to stay with the stock OTs you should be using a 4 ohm speaker load - either one pair rated at 4 ohms or two pair of 8 ohm speakers wired in parallel.

My recent conversion of one of these amps to use 12BH7 output tubes allows the use of the stock transformers with 8 ohm speakers. I'll be updating that thread soon. http://www.audiokarma.org/forums/in...0-or-8600-conversion-to-12bh7-outputs.824135/
 
See my edited post above with the pinouts of the two tubes.

Going with a 12AX7 does give you more options if you want to try different brands or some of the new production versions.

If you're going beyond a simple change from 6EU7 to 12AX7 you should remember that the changes Dave made are based on his decision to replace the output transformers. That decision was made because the stock output transformers were designed for use with 4 ohm speakers and he found that they performed very poorly when more common 8 ohm speakers were used. If you decide to keep the stock transformers some of those other changes may not be appropriate. You might want to ask about that on his mod thread. If you decide to stay with the stock OTs you should be using a 4 ohm speaker load - either one pair rated at 4 ohms or two pair of 8 ohm speakers wired in parallel.

My recent conversion of one of these amps to use 12BH7 output tubes allows the use of the stock transformers with 8 ohm speakers. I'll be updating that thread soon. http://www.audiokarma.org/forums/in...0-or-8600-conversion-to-12bh7-outputs.824135/
I already changed the OT to the 8ohm. Thanks
Fred
 
Ok, si i did connect the heaters and now everything turn on. There’s a lil humming but nothing serious for now. The probleme is that as soon as i put my rca cable in the loud buzzing is starting again ?! I’m still waiting on my .1 250v in lieu of the old .01 ceramic disk on the 12ax7. Could it be that ?
 
If I hook my phone there’s music and somewhat no distortion but as soon there’s a lil base in the voice, the tweeter and middle have distortion the more I raise the volume it raises with it. Only on the right channel tho
 
So a little update here guys, everything is working here, I got sounds in both channels (I forgot a ground on my speakers terminals). But now I have a some what loud background hum on the right channel but can’t seems to find where it’s coming from. Any thoughts ?
 
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