Tube/bias question.....

[RedB4Black]

My amp has a plate voltage of 560

I put in some Ruby labeled SED winged C tubes that I had that had the following measurements.

PC: 43
TC: 4900 (on three) and 4825 on the fourth

Based on the weber bias calculator, I should be biasing at 32Ma. The range on the bias pot won't let me get the hottest tube below 38Ma and the other tubes range from 34 to 36Ma.

My question is...

What do the PC and TC mean on the tubes. Should I look for higher or lower numbers on another set to allow me to get the amp biased to the proper range?

 

[steve_k]

My amp has a plate voltage of 560

I put in some Ruby labeled SED winged C tubes that I had that had the following measurements.

PC: 43
TC: 4900 (on three) and 4825 on the fourth

Based on the weber bias calculator, I should be biasing at 32Ma. The range on the bias pot won't let me get the hottest tube below 38Ma and the other tubes range from 34 to 36Ma.

My question is...

What do the PC and TC mean on the tubes. Should I look for higher or lower numbers on another set to allow me to get the amp biased to the proper range?

What was the rating on the tubes you pulled out of it? if this is the CCV, Mark does leave a small bias range in it. He likes to run his about 80% dissipation though. Running them much lower, you have already so much gain on the amp, it just gets more gain and much quicker. As long as you are under 80%, I would not worry about it. 560V sounds kind of high though. Did you measure that yourself or was told that number? Seems like mine was around 520V with the Cameron/Mercury iron. to answer your question though, yes, a lower rating will yield a lower bias point.

Steve

 

[RedB4Black]

My amp has a plate voltage of 560

I put in some Ruby labeled SED winged C tubes that I had that had the following measurements.

PC: 43
TC: 4900 (on three) and 4825 on the fourth

Based on the weber bias calculator, I should be biasing at 32Ma. The range on the bias pot won't let me get the hottest tube below 38Ma and the other tubes range from 34 to 36Ma.

My question is...

What do the PC and TC mean on the tubes. Should I look for higher or lower numbers on another set to allow me to get the amp biased to the proper range?

What was the rating on the tubes you pulled out of it? if this is the CCV, Mark does leave a small bias range in it. He likes to run his about 80% dissipation though. Running them much lower, you have already so much gain on the amp, it just gets more gain and much quicker. As long as you are under 80%, I would not worry about it. 560V sounds kind of high though. Did you measure that yourself or was told that number? Seems like mine was around 520V with the Cameron/Mercury iron. to answer your question though, yes, a lower rating will yield a lower bias point.

Steve

Yes, it's the CCV. I measured it with my Weber Bias Rite. Three tubes measured PV 559 and the fourth measured at 555. Not sure how accurated the Weber is for PV. I'm sure there is a more accurate method with a DMM.

The tubes that are in there now are Chinese el34-Bs. There aren't any ratings on them. I'm running them at about 30-32 Ma on three of the tubes. One is a little mismatched and is at 36.5Ma. Sounds good as it is, I may just leave it alone and not worry about a tube swap.

 

[Capulin Overdrive]

could maybe swap around the SED's, and see if you could get it evened out some.


i don't know what i'd do in your shoes? probably run the tubes a few days, and order some with lower numbers.

 

[steve_k]

The voltages are most likely correct. My CCV has a plate voltage of 565 on high and 455 on low. Big headroom.

I have to check what my numbers are at home. I also owe you an email.

He must have changed trannie designs somewhere along the way. at 110V input, seems I was getting 520-530 PV.

 

[RedB4Black]

could maybe swap around the SED's, and see if you could get it evened out some.


i don't know what i'd do in your shoes? probably run the tubes a few days, and order some with lower numbers.

Yeah. I tried swapping positions. Didn't really work. The current tubes in there now are fine. I pulled the winged C's out of my Uberschall to try. That amp has a high PV too, but the bias pot obviously has a wider range.

 

[RedB4Black]

The voltages are most likely correct. My CCV has a plate voltage of 565 on high and 455 on low. Big headroom.

I have to check what my numbers are at home. I also owe you an email.

What do you mean by low? Half power mode or the pentode/triode switch?