I thought this looked like a really useful table on bias current for output valves.
The top of the page allows the super techie types to do an exact calculation based on measured voltages in your actual amp and the configuration of the circuit.
The featured picture is actually all the tools ( apart from the right screwdriver). It is simply a multi-meter and a special adapter. You plug the adapter into the output valve socket and then you plug the valve into the adapter. The multi-meter scale is set to the 200 millivolts range. It then actually reads the value of the bias current in mA. Use the table on the link below to finf the right bias current for the vlves in your amp. Of course you need to find the poentitiometer to set the bias. If you are not sure then get a ualified technician to do it. There are a lot of lethal high voltages in your amp !
Further down the page is a very useful table on bias current for output valves and you can make your own selection. Its a nice summary
I tried running the 6V6 in my own amp at 25mA and to be honest it sounds “thin” and characterless. This was for a voltage of 250 volts. The output valves run cool and will last probably 600 years ( hee hee) and so I have gone up to 30mA and what a difference. A louder and warmer sound.
Click here to see the page
Useful Table on Bias current for output valves
Yours is a brilliant blog.
I have just bought six JJ 12AX7s from you, planning to use them for a guitar dude on Wednesday. If they’re OK then I’ll be needing some more from you for another bloke’s Fender Twin (late 90s reissue.)
I do all sorts of stuff exactly like what you describe on here. I agree so very very much about resistors/capacitors etc!
Also the Fender Hotrod/Blues/Deluxe series (the reissues are worse, with their chintzy-ditzy-cheapo PC boards!) are what one would charitable call “not as well-manufactured as they could be”…. (No aspertions are being deliberately cast at Mexicans here! I’m sure they are trying to do their best…) I have done probably 40++ of these for guys in Liverpool and Lancs in the last few years alone, as all their 12AX7 anode load resistors and phase-inverter couple caps begin to fail, sort of all about the same number of hours’ use….
And as for the upside-down 6L6 power amp PC board…..(talk about dry joints!)