Trim pots and dual rec.

[mbbguitar1]

So we all know that the dual rec is a set bias amplifier. I just read on the eurotubes website that a dual rec, or any other amp that is a "set-bias" amp, is usually set cold and should have a trim pot installed, which would greatly improve the tone of the amp. Has anyone here heard this before? Has anyone here done this, and is the tone better? Please advise! Thanks, mbbguitar1

 

[Boogiebabies]

 

[mbbguitar1]

Thanks for the info. That was exactly what I was looking for.

 

[CudBucket]

Well, the DRs from the early-mid 90s were biased hotter than the current 3 channel models and many prefer them to the newer models.

 

[ylo]

Adding bias trimpots has some pros and cons:

(+) You can use a wider range of power tube brands and performances and tweak for the correct idle current.

(-) In Boogies, you have to cut PCB traces and add components or wires to go to off-board components. This can get messy, and I suppose voids the warranty. If you screw it up you can do some serious damage, for example melted power tubes.

I think Mesa's claim that bias adjustment is unecessary is a complete pile of crap -- the wrong bias can shorten tube life. On the other hand, maybe I am deaf, but I have never noticed much difference in tone for different bias settings in my 70's Fender Twin and 60's Gibson Lancer tube amps, which I modified with bias trimpots. I have decided not to bother adding bias pots to my own Mesa.

 

[G.I.G.]

I know there are people out there that will disagree, but I would be very hesitant to put a bias trim pot on either of my Boogies.

If you read Randall Smith's article regarding bias and why their amps are fixed bias, it makes sense. Sure, maybe Mesa wants to sell more of their tubes, but their profit margin is much larger on amps then on tubes, and I don't think they would sacrifice amp sales by making their amps fixed bias, only to sell a few more tubes. Like Randall Smith says "we're in the amp business, not the tube business".

If you have an electronics background and could properly install a trim pot and adjust the bias correctly everytime you changed power tubes, then maybe it's not a bad idea. I own a Dual Rec and a Rectoverb, both of which I love. I am very content with the tones I get out of both and have no desire to add a bias trim pot to either.

One other thing to point out. With a lot of the newer Boogies (RK, Roadster, Stiletto, etc.) that have multi-watt channel assignable power, you can drive the tubes harder in the 50 watt mode vs. 100 or 150 watts if getting more power tube saturation is your deal. It's another option that at least in my opinion, elimnates the need for adjustable bias.