Re-Bias a Dual Recto?

[steelhorse]

I have a 94 DR, has new tubes (6L6 GT's and GT pre's) sounds great and is doing very well. I had rack mounted boogies back in the 80's and MK III's and of course was told I didn't need to re-bias if I used boogie tubes. Coming from a mostly Marshall background for many years and finally getting one of the amps I've wanted for many years, does this amp require re-bias when re-tube the output valves and if so what are the bias ranges and where are the bias pots located?

Is there anywhere online that has a guide?

 

[hoobafrank]

The way I understand it, most boogies are fixed bias and the only change you can do is throw el-34's in there and flip the switch (if it allows it). Those are the only bias adjustments you can make. That being said when you buy tubes, make sure you specify that you are putting them into an amp with a fixed bias. At least thats what I've been told, and what I have practiced.

-Chris

 

[droptrd]

Thats right. The DR's have a fixed bias. Let your tube supplier know that they are going in a mesa DR and you should be fine. Or you can buy mesa tubes and you will be fine. Mesa only sells tubes that fit in the bias range of thier amps. GT's will work also if you use this conversion chart to convert the mesa color code to the GT rating scale

MESA/GT
red/4
yellow/4
green/5
gray/5
blue/6
white/6

 

[steelhorse]

Thanks for the info. I suspected this was the case but wasn't sure so thought I'd better ask.

Also not sure what the color code thing for GT means, there are "4's" in there currently so I'll look that up.

Which are better for hard rock, metal type music like Alter Bridge, Killswitch Engage, Metallica?

 

[droptrd]

Mesa uses a color code for their tube rating system. - red yellow green etc...
Groove Tubes uses a number scale. 1-9 So if you buy a GT in 4, 5, or 6, you will be able to drop em in your mesa and go. The lower the number, the earlier the distortion - but you loose punch and clean clarity.
1-3 = early dist. 4-6 = med 7-9 = late dist. (but you only want to use 4-6 in your DR)

 

[steelhorse]

Awesome, thanks!

 

[Juancito12]

Mesa and color matched tubes are fine and safe but when I bought my recto I took it to a local tech an they installed a bias pot, new output tubes, and biased it to a warmer tone using a scope. Now I can dial in a good tone with any tubes. It allowed me to try the SED Winged C's which I love in my recto.

 

[steelhorse]

I think I'm going to stick with what's already in there; GT-6L6-CHP Quartet

These: http://www.groovetubes.com/GT-6L6-CHP_Quartet_P2174.cfm

& http://www.groovetubes.com/GT-12AX7-R3_P1586.cfm