Ampeg B-15-NF question

[mresistor]

Hi guys -  Concerning an Ampeg B-15-NF would you consider a static bias setting with Sovtek 6L6WXT power tubes right about 73% of 30W acceptable?   


PV - 493 VDC
PI -  45 ma


Or should I up the 100K bias resistor to get the static dissipation down to around 60% ?  If so what value would you suggest..  ?


https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_b15nf_schematic_4_65.pdf

[sluckey]

Or should I up the 100K bias resistor to get the static dissipation down to around 60% ?  If so what value would you suggest..  ?

You need to decrease that 100K in order to decrease plate current. Or you could increase the 47K for the same results.

[shooter]

by adding 1 Ohmer's you can monitor real-time results, I was pretty shocked at how much current hard pickin likes.
even at 60-some % Average current was getting close to the warning zone.


but these are guitar amps, so usually tone wins over engineer, hands down   

[mresistor]

Oh yeah  sorry  decrease   thanks..    And it's a bass player that will play it.  Old guy like us so not going to play that loud.   I was thinking more around 60% or even less would be better for the amp.


Thanks guys.

[PRR]

...shocked at how much current hard pickin likes....

That extra on-demand power goes to the load, not the tube. And is ultimately determined by supply voltage and load impedance, not bias.

If 63% is the coolest you can go with THIS set of tubes, find a way to get less bias current (more bias voltage), so when you replace tubes and get a "hot" set you can dial it down.

[mresistor]

Thanks PRR   I replaced the 47K with a 56K and the amp quiescent current is at 50% and I feel a whole lot better about it.  It also sounds pretty good to me.


Shooter I have a Hoffman bias checker I made eons ago .. used it and trying to keep the amp as stock as possible.