Adjustable Bias For Mark III Simul-Class Boogie?

[jamaicajeff]

I'm looking for info or a kit to mod my Mark III Simul-Class so that I can adjust the Bias current and get rid of the grainy sounding power section. Right now I have 2 GT EL34's S-7(V6, V9) and 2 GT 6L6GE (V7,V8)H6.
I did some voltage and bias current checks and this amp is running much to cold. With just the EL34's (half-power) V6 and V9 draw 25.3 ma which isn't too close to the 30 max that the bias probe manual states. At full power V6 and V9 draw 25.3 ma which is on the nose according to the probe manual which calls for 25ma; however, V7 and V8 only draw 19.4 ma. These tubes are way under biased and I can hear the grind. The EL 34's are doing all the good sound performance while the 6L6's are being suffocated. Can anyone give me instrutions or is their a kit out their to convert this amp. I would like to hear its potential after owning it for 16 years. I am very competent with a Volt meter and a solder iron and have done several good projects in the past. Any help will be sincerely appreciated.
Jeff

 

[Shai`tan]

There is a post here on this forum that shows very good screenshot closeups of the bias mod for the Mrk III. I showed them to my amp tech, and he knew just from looking at the screens how it was done. And he is doing the same mod for me, as well as a complete cap job.

And you are right. We tested the tubes and the bias, and no way is the bias set correctly for my Mrk III to the Svetlanas I use. Yet Mesa Boogie says this amps bias is set for THEIR tubes.

I will do a search for the post right now. Then post the link.

http://forum.grailtone.com/viewtopic.php?p=500&sid=78cc45ebdc8c48c02efb45b6711efa36

I hope this is as helpful to you as it is for me.