DrZ Maz 18JR Bias Question

Stan Malinowski

Gold Supporting Member
I believe my Maz 18JR Combo is a Class A amp (I can't find any info on their website which clearly states this) and I would like to re-tube. If the amp is Class A then theoretically I do not need to re-bias the power tubes. Are my assumptions correct (Ie is the Maz 18JR Class A)?

Any 18JR owners have recommendations on brands of power and pre-amp tubes that they favor?

Thanks,
Stan
 

arfy

Member
I emailed Dr. Z about getting spare tubes for my Maz Jr and he advised to get "mid range Tesla EL-84's tightly matched and your good to go." Lord Valve(NBS Electronics) is a good online source. The Maz Jr. is cathode biased, I think, and a pair in the middle of the rating scale shouldn't need any bias adjustment to the amp, which would probably mean changing the cathode resistor value in a cathode biased amp.
 

nek

Member
Originally posted by AlexT
DrZ recommends GT EL38S #6 - and yes, no need to bias.

Alex
Right, EL84. AlexT and arfy are saying the same thing. The S in groovy tubes parlance is Tesla. Middle range for GT is 4-7. Anywhere in that range ought to do it.

My Maz JRNR came with JJ 12AX7's in the first two positions and a Sovtek 12AX7LPS for the phase inverter. I really have had no reason to change them. Every once in a while I ponder switching out the Sovtek GZ34 for a Mullard. I don't know, it just feels kind of like overkill.
 

Taller

Silver Supporting Member
I get my JJ/Tesla tubes from Bob at eurotubes. Great prices, great service and he's very knowledgable about tube amps and loves to talk about them.

He's kind of nutty looking on his website, but I work around electronic engineers all day long and he looks normal to me!


eurotubes
 

Blue Strat

Member
No, they're not all self biasing. The Rt 66 (and possibly others) are not self biasing.

All of the EL84 amps are self biasing however.

Consider using the NOS Tesla (not JJ) El84s which have higher gain and more bite than the JJs.
 


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