Traynor YBA-3 Custom Special - B+ level

[GussyLoveridge]

Hi Folks,

I'm working on a Traynor YBA3 Custom Special circa early 70s.  4 EL34s. I have ~560 VDC on the plates and maybe ~540 on the screens.  They are running around 34 mA per tube which I calculated as running about 76% of their capacity.

Are these numbers way too high? 

Schematic calls for 540 VDC on the plates and 536 on the screens.

Is this just because of higher mains voltages to the house these days? 

Thanks dudelingers. I love this place.

 

[mjrippe]

You are well within spec.  Rock on.

 

[CJ]

what kind of tubes? 

metal base mullard's will be ok,  JJ garbage will die a quick death,

 

[GussyLoveridge]

Hey folks -

mjrippe:

Thanks, I appreciate the help.

CJ:

I have been using JJs. They have been reliable for me. I have put them in nearly every amp I have worked on and never had a problem with the fidelity or longevity. What is your experience with them that has led you to believe that they are a sub-par valve?


ANOTHER QUESTION:

What is the correlation between bias voltage (negative voltage) and bias current?

I understand that the more bias voltage applied, the more the tube is shut off or less quiescent current. 

I am under the understanding that the bias voltage should be ~10% of the B+.

But is there anything to say that if you'd like to rise the bias currently by say 5 mA - that you would lower the bias voltage by X vdc?

 

[PRR]

> I am under the understanding that the bias voltage should be ~10% of the B+.

No, not for most audio tubes.

> .....if you'd like to rise the bias currently by say 5 mA - that you would lower the bias voltage by X vdc?

No. In principle it might be calculated. In practice you MUST measure current.

 

[abbey road d enfer]

I am under the understanding that the bias voltage should be ~10% of the B+.

It appears to be so with the typical big bottles (6V6, 6L6, EL34, 6550...) but utterly wrong with small bottles like EL84, 11-19V bias for 250-375V B+

But is there anything to say that if you'd like to rise the bias currently by say 5 mA - that you would lower the bias voltage by X vdc?

As PRR wrote, no simple equation. Between different grades of the same type of tube, quiescent can vary +50/-30% for a given bias voltage.

 

[GussyLoveridge]

Thanks folks - I do appreciate the help so much.