[Gallaine]

Not sure if this is right forum, but I put it here because my question is about tube matching for a Stax 006t amp.

Anyway, I've been doing some reading about the Stax 006t amp (since I bought one) and wondered if the 6FQ7 tubes it uses need to be matched - after all, I want to do some tube rolling; yes, of course, after I've had some time to become familiar with the amp.

I've read an article or two about matching power tubes but came across some literature that suggested that preamp tubes did not require matching. The next question that came to my mind is whether or not the tubes in the Stax amps are "power" tubes. So, what do you think?

Too match or not too match, that is the question.

 

[kuma]

Quote:

Originally posted by Gallaine The next question that came to my mind is whether or not the tubes in the Stax amps are "power" tubes. So, what do you think? Too match or not too match, that is the question.

I'm not hard-core tube head. But my tubed preamp also uses 6FQ7 or ( 6CG7).
They are not a *power* tubes, I don't think.

They might be functioning like power tubes in your fone amp since you don't need as much as power as driving speakers.

I've always used matched pair whether power or small signal tubes.

 

[kevin gilmore]

In a stax 006 or 007 there are 2 pots per channel that
need adjusting when you change out the tubes.

In a 006 you try to balance the sections of a tube.
In a 007 you try to balance 2 tubes to be the same.
(2 tubes per channel instead of 1)


One pot is the dc balance between the sections of a tube
and is measured between pins 3 and 4 of the headphone
connector. (2 and 5 for other channel) Set it to zero.

The other pot is the dc offset and is measured between
pin 3 and chassis (pin 2 and chassis for other channel).
Set it to zero.

You will have to repeat this a number of times to get it right.

 

[Hirsch]

In an amp that has the bias adjustments Kevin has described, getting the tubes matched from the start is less critical than in an amp that doesn't have those adjustments. However, if you start with reasonably well matched tubes, variations in bias voltage between the sections and between the tubes will be less. Further, tubes that are reasonably well matched at the start may wear at around the same rate.

Kuma is also correct in that the 6FQ7 is not a "power" tube in the normal sense, but rather a small signal tube. Matching and bias adjustments are usually not as critical in small signal tubes, but since Stax has provided a way to make the adjustment, my guess is that performing it will get the best performance out of the amp.

My personal rule of thumb is that even with small signal tubes, I try and keep all triodes, both within the tube and between tubes, in a ten percent range, even in amps that "self-bias" and especially in amps that don't adjust bias at all.

 

[Gallaine]

Thanks for the information.

I've never manually adjusted bias before. Do I need any equipment to do it? I haven't taken delivery of the amp yet so maybe when I see it I'll understand.

 

[kuma]

Quote:

Originally posted by Gallaine Thanks for the information. I've never manually adjusted bias before. Do I need any equipment to do it? I haven't taken delivery of the amp yet so maybe when I see it I'll understand.

If your amp is not self-biassing, you need a voltage meter.

http://www.avalonrise.com/catalog/pr...roducts_id=172www.avalonrise.com/catalog/product_info.php?products_id=172

I won't recommend start tube rolling till you get the handle of what the amp sounds like with stock tubes first, tho.