Driftwood Purple Nighmare bias

[russell.hollmes5]

Whatsup guitar dudes and dudettes!

I recently got a purple nightmare, I really like it I know it got mixed reviews but I think it sounds pretty beefy.

Anyways I didn’t get a manual with it and after googling, searching their website top to bottom, searching YouTube, searching this forum…also I emailed Marek, no response yet.

I cannot find ANY info on what to bias the tubes to. There is a section on the back of the amp to plug in a multimeter and pots to adjust the bias and I am a technician by trade so I feel confident doing this, I just need to know what value to set these to. My amp came with 2 6L6 and 2 KT88 like many of them do. I checked the bias that the amp came with but I also want to verify that the tubes weren’t improperly bias’d by some other DIYer.

Thanks for any help!!

-Russell

 

[bugsy5150]

I bought a Darkest Nightmare new with the same tube set up as yours, here’s how the 6L6’s were biased from Driftwood.
Thirteen reading is watts!! Hope this helps!!

 

[strungout82]

Hi. It is worth a mention that if you use the bias test points of your Purple Nightmare then you are measuring only one tube of the pair (V6/9 or V7/8). I got this info from the Marek himself.

 

[russell.hollmes5]

Update!! Marek emailed me a copy of the manual and this:

i would set the bias for the 6l6 at around 32mA (=32mV reading) and
around 40 for the KT88s.

Yeehaw!! ?

 

[FourT6and2]

Update!! Marek emailed me a copy of the manual and this:

i would set the bias for the 6l6 at around 32mA (=32mV reading) and
around 40 for the KT88s.

Yeehaw!! ?

You should really measure your specific amp's plate voltage. A manufacturer's recommendation is just that. You wall/mains voltage changes things and each amp can have behave differently. If you're a technician of some sort, whip out the DMM and measure your amp's plate voltage. Then you'll know your max bias @ 70%.

6L6 = 24 watts
Assuming 523 Vp...
25mA = 55%
32mA = 70%

6L6GC = 30 watts
Assuming 523 Vp...
25mA = 49%
32mA = 56%

KT88 = 42 watts
Assuming 523 Vp...
40mA = 53%

 

[FourT6and2]

I bought a Darkest Nightmare new with the same tube set up as yours, here’s how the 6L6’s were biased from Driftwood.
Thirteen reading is watts!! Hope this helps!!

View attachment 379355View attachment 379358

That's pretty cold... Like ~50%. Probably shipped that way to keep keep warranty claims down. Might be hot enough to get out of crossover distortion but hard to say without a scope. But if it sounds good, it's all goooooood