MKIII with 7581A's

[RussB]

I put a set of JAN Phillips 7581A power tubes in my MKIII recently. I gotta say these do sound pretty friggin' good. I had been running a set of SED EL34/6L6's, and thought highly of that set-up.

My MKIII was modded to have an adjustable bias. I'm running the outer pair at 52mA (in Class A), and the inner pair at 40mA. I had to drop the control grid resistors to the outer pair to 82k (vs. the 220k factory) to get the tubes to be better "balanced".

I got the 7581A's from Mike @ KCA NOS Tubes. Not cheap by any means. My amp also has a Telefunken in V1, Ruby "Silver Plate" in V2, and a 12AY7 in V3.

 

[zeppman]

RussB, would you say they are worth the money? They are very expensive.

 

[908ssp]

I run some of those in my Vibrolux where I want nothing but clean wide frequency sound. In my MKIIC+ I want the power tubes to add some dimension to the sound so I run Sylvania STR 454s on the inside pair and E/H 6CA7 on the outside pair. It sounds darn good but I still need to do some experiments with the pre-amp tubes.

 

[RussB]

...so I run Sylvania STR 454s on the inside pair...

STR-415's are the Sylvania's (which are Phillips)

STR-454's are SED 6L6GC's

 

[RussB]

RussB, would you say they are worth the money? They are very expensive.

Mike claims they will last 5 times longer than any "new" production tubes. That's a tough claim to quantify, though...and they may still work OK, but will they still sound good in 2, 3, 4 years?

I wish there were simple answers to questions like yours...