I have two el34's in ultralinear operation. The resistance from the center tap on tube 1 is 72.4 and on tube 2 it is 83.4. V drop from center tap to plate on both tubes is 2.8. This leaves me with plate currents of 38 and 34. The tube biased lower has much less glow to it compared to the right why is this and how do i fix it.

 

I have two el34's in ultralinear operation. The resistance from the center tap on tube 1 is 72.4 and on tube 2 it is 83.4. V drop from center tap to plate on both tubes is 2.8. This leaves me with plate currents of 38 and 34. The tube biased lower has much less glow to it compared to the right why is this and how do i fix it.

Can you post a circuit diagram?

 

Can you post a circuit diagram?

Excuse the red circles.

 

When you say "much less glow" are you referring to the glow of the filament?

 

When you say "much less glow" are you referring to the glow of the filament?

Yes, it is not as bright as the other tube

 

why?......getter shadow.

How to fix it?......you can't.......maybe look at tube with different angle.

 

Try interchanging the two tubes.
Moving the tubes in and out of the sockets could help clean up the contacts.
If the same tube is glowing much less maybe it is time for some new tubes.

 

why?......getter shadow.

How to fix it?......you can't.......maybe look at tube with different angle.

I mean with measurements i can tell the bias is uneven which is causing this. how do i fix it,

 

Try interchanging the two tubes.
Moving the tubes in and out of the sockets could help clean up the contacts.
If the same tube is glowing much less maybe it is time for some new tubes.

Already have new tubes and have cleaned sockets

 

Im just curious why the readings would be different.

 

If you interchange the tubes does the balance change?

 

Oh, I see now. You are measuring the DC resistance of the transformer and using that to determine plate current via I = V/R.
I have never seen anyone do that.

 

If you interchange the tubes does the balance change?

no

 

no

In that case, I say one tube is different from the other, filament wise. I have not seen this before.
Do you still have the old tubes?

 

In that case, I say one tube is different from the other, filament wise. I have not seen this before.
Do you still have the old tubes?

yes

 

yes

So now you have four EL34 tubes. Find if the low glow applies to only one of the four tubes.

 

So now you have four EL34 tubes. Find if the low glow applies to only one of the four tubes.

two el34 tubes. it applies to only one

 

two el34 tubes. it applies to only one

Then nix that tube and use the old tubes while you wait for one or two new tubes to arrive.

 

Then nix that tube and use the old tubes while you wait for one or two new tubes to arrive.

i have done that. this happens regardless of tube

 

And idle current of 38 ma in one and 34 ma in the other, I would think the filaments are ok.
A ~ 10% difference.
Most tube circuits have wide tolerances. It was just a drive by comment on the tube glow.........I haven't been keeping up on your project or mods.