Had no idea Boogies were biased this cold!

[CitizenCain]

I know about the fixed bias and the rationale behind it. I was doing some work in the shop and thought I'd test my Mk I reissue just to see where it was biased.

Man, I can't believe it sounds as good as it does with biasing like this. I've got some Svetlana 6L6GCs in there. They're measuring around 475v and 35 mA. That's cold! I switched to the Tweed power setting and it's looking around 400v and 25 mA.

The Weber bias calculator says I should be around 44 mA on high and 52 mA on the Tweed voltages.

Just for grins I put a set of Mesa 6V6GTAs in there. Running on Tweed power they get 405v and 6.4 mA. That's about 3w idling. And it sounds frickin' awesome with these tubes in it!

Does anyone here mod their amps for adjustable bias? Do you get enough difference in the tone to make the effort?

 

[stokes]

If it is worth it "tonewise" is totally up to how you play your amp,and your perception of what sounds good.If you play with a lot of preamp distortion,it may not be that noticeable as it will be at cleaner settings.What makes it worthwhile is the fact that with an adjustable bias,you are no longer locked into using Mesa tubes or tubes that are pre tested to fit your bias range,you can use any matched set of output tubes,I like NOS tubes,and to use them in a stock Boogie you have to get lucky,with the adj.bias I can use any tubes I have.

 

[pfflam]

Do you have to do any to the bias, etc. to be able to use 6V6 in the Mark series?

Can you plug them in any output tube position in a simul-class green stripe Mk III?

Very good question . . . as I have about 10 NOS stock 6v6s laying around and want to try them out.



And where can I get information on getting or doing a Bias mod?

I would love to have one in my Old-School 60W SOB, so that I can pop in Old Tubes without worry (I come across lots of old tubes) . . . love to have one so that I could test with a DMM and then adjust without removing the chasis?

any ideas on if such a thing is possible?

 

[stokes]

Do you have to do any to the bias, etc. to be able to use 6V6 in the Mark series?

Can you plug them in any output tube position in a simul-class green stripe Mk III?

Very good question . . . as I have about 10 NOS stock 6v6s laying around and want to try them out.



And where can I get information on getting or doing a Bias mod?

I would love to have one in my Old-School 60W SOB, so that I can pop in Old Tubes without worry (I come across lots of old tubes) . . . love to have one so that I could test with a DMM and then adjust without removing the chasis?

any ideas on if such a thing is possible?

I wont touch the 6V6 issue,but the bias mod is simple.Look at a schem for the amp and find the bias circuit,there is a 10k resistor (might be different value in your amp) and change it to a 20k cermet pot,if this resistor is a different value than the one in the schem just use a pot twice the value,that way the bias voltage you have with the fixed resistor will be right in the middle of the pots range and you can adjust up or down for the tubes you select.