Mark III bias

Hi
Thanks for a great forum.

I'm a new tube owner, got me a pair of stock mark III
and a stock Pas-3x. With the original Dynaco tubes.
In the mark III it's the 6550. Sound great
But maybe a little flat at constant baseloops, at some low frequency. I must send the tubes for testing.

Checked the bias, it was 1,36 in one. 1,46 in the other.
I would like to keep the tubes as long as i can. So my question is: Whats the lowest i can set the bias, before it underperform? I did set it at 1,4. After 45mins of playing. Still at 1,4. Thats good i think?

I'm from Sweden, so runs 230V.

Regards Niklas

NikmarkIII wrote:Hi
Thanks for a great forum.

I'm a new tube owner, got me a pair of stock mark III
and a stock Pas-3x. With the original Dynaco tubes.
In the mark III it's the 6550. Sound great
But maybe a little flat at constant baseloops, at some low frequency. I must send the tubes for testing.

Checked the bias, it was 1,36 in one. 1,46 in the other.
I would like to keep the tubes as long as i can. So my question is: Whats the lowest i can set the bias, before it underperform? I did set it at 1,4. After 45mins of playing. Still at 1,4. Thats good i think?

I'm from Sweden, so runs 230V.

Regards Niklas

Distortion will increase with lower bias. 1.56 is nominal. If the tubes don't reach thet they are
most likely "worn out", this also affects how much power it can give.

New matched 6550 might be what you need to get needed power.

peter ( also from sweden )

They do reach that bias i think. 1,56 is a little high nowdays when voltage in wall socket is 230?

NikmarkIII wrote:They do reach that bias i think. 1,56 is a little high nowdays when voltage in wall socket is 230?

You could go down to 1.50 if you want. Byut there is no problems for OLD tubes and certainly
not JJ-6550 . What you don't want is much over 1.60

Thanks!
I gonna set them to 1,5 then
I don't hear any dist at 1,4. Only a little fluctuating bass in one of them. Like a idle problem in a car, it goes a little flat.

What company did the original USA dynaco 6550 tubes?

NikmarkIII wrote:Thanks!
I gonna set them to 1,5 then
I don't hear any dist at 1,4. Only a little fluctuating bass in one of them. Like a idle problem in a car, it goes a little flat.

What company did the original USA dynaco 6550 tubes?

TungSol made the 6550.   The ones  Dynaco rebadged - i do not know of their origins.

I use JJ 6550 by obvious reasons and find them perform ok.

I did some test with higher bias. Did not improve anything.
Will get 4 new JJ tubes to start with.
Thanks for your help Peter!