How to order tubes for desired bias effect? Hot, Cold, Med

[danipman]

Tubes come in different ratings (GT 1-10, Boogie/Fender have colors).

I'm more interested in trying out other tubes but I want to achieve certain performace outcomes, most to order tubes that I can control the power amp breakup, eg Softer tubes for less clean headroom.

Since Boogies (Mine is a MarkIIC+) have the fixed Bias and from what I am reading, different bias on the Class A and Class AB circuit I am going to assume that slightly different tubes might perform differently.


I live near Doug of Doug's Tubes so I can obtain tubes within a certain spec. He has a tester and labels the boxes.

How do I order tubes to work with the fixed bias as a fixed point, and the tube as the variable?

If I wanted a tube to distort sooner, what would I ask for?

If I wanted Tubes that had more headroom, what would I ask for?

What is the optimum spec for Class A circuit?

What is the optimum spec for the 60Watt citcuit?

I believe the term is transconductance?

Any assistance appreciated

Dan

 

[zeppman]

I believe the hotter the tube runs, the quicker it will break-up. Running tubes too cold will make it sound very sterile though..so be careful.

 

[Timbre Wolf]

Have you asked Doug these questions, Dan? My guess is that you haven't, yet, because you wouldn't be asking us.

In my experience with Doug, he is very capable of answering such questions. He has been quite helpful to me in the past, and was willing to take a bit of time to get my order right (and make useful suggestions at the same time). Give him a call, and tell him what you'd like to do - he's a nice guy!

- T

 

[RussB]

#1 there is no "optimum bias point"

#2 Class A , LOL! :lol: in Mesa's case, that means class a/b running at 100% or more of max plate dissipation. In that case, you want tube that draw little natural plate current (IMHO, of course)

#3 Talk to Doug

 

[danipman]

Doug is a very knowledgeable and nice guy and I have purchased a bunch of tubes from him in the past. However Doug doesnt collect Boogies and I havent seen one in his house on my visits there.

The information I am seeking is what are the recommended readings a tube should follow to be best suited for the fixed bias circuit the Boogies run on.

What makes the tubes that Boogie sells suited to the circuit in the amp?


If you tell me a tube that runs hot will breakup sooner, how do I specify that? If I have tube X, but want a replacement tube to be a little dirtier or a little cleaner, what would be the measurable criteria?

The reason I am asking here is because we all have Boogies and most are tied to a fixed bias. Since I cant tune my amp to the tubes, I wish to have some way to select tubes to match the sound I want to get.


DW

 

[screamingdaisy]

+1.

Tell Doug what amp you have, and what you're trying to do gain/sound wise and he'll select what'll work best.

And don't worry about sounding dumb....I've asked him plenty of dumb questions and he's always been very helpful.

 

[RussB]

For the record "Fixed Bias" is the way all class a/b amps operate, some have variable resistors (potentiometers) to adjust the grid voltage, while some use a simple resistor. Either CAN be adjusted, and in the case of Boogies, you need to swap out a resistor.

Old Fender's and Marshall's all have fixed bias, as do most amps out there.

Doug CAN help you choose the right tubes (He's helped me!)

So can Lord Valve and Mike @ KCA NOS Tubes. They know what will work in your particular Boogie.