[hsusmann]

I have been restoring a Philco 86 all week and
finally got it all put together and running again.

I noticed that the 80 Rect. tube has a faint
blue glow between the filaments and the plates
indicating a gassy tube.

I don't have much experience dealing with gassy
tubes. From what I've been reading online
some people run with them as long as they
are still working. Others say replace them.

I also was reading that if you leave them
on about half voltage for a couple of days
the gas may become absorbed by the getter
material.

Just wondering if anyone else here has some
words of advice?

The radio seem to work fine and I get good
B+ voltage etc...

Thanks,

Herb S.
Ithaca NY

[codefox1]

Seems to come up every week or so, but it's a crap shoot at best. 80's are neigher rare or expensive, and if it were mine I'd get a better one lest the power transformer, etc... take the hit.

[morzh]

I think I git 6 or 7 of them at about 2 bucks each a year ago on eBay.

[hsusmann]

OK, thanks for the advice. I do have some other 80 tubes around here but they are the ST type not the globe type as the gassy one is. I was hoping to use the globe type but sounds like it's best not to use gassy tubes.

I am doing a side experiment where I'm running the gassy tube on a lab power supply on about half filament voltage. I'll let it go several days and then check to see if the blue glow is still there when it's in the radio.

Don't know if you're supposed to run plate current for this fix or not. Will start with just half filament current for now.

Herb

[Phlogiston]

That's a good idea, but why not run it at 5 volts?

[hsusmann]

I don't know why you are not supposed to run it at full filament voltage at first. I've read that you do it at half voltage for a few days then ramp it up to full for a few more days.

Don't know the reason yet...

Herb

[codefox1]

Glad you asked. If you can run the set up slowly with a variac and a good old fashioned analog milliamper meter (say 500 MA) between the 80 filament and the first filter capacitor, you can get a good idea of what is going on as the set slowly warms up. Chances are if you have not replaced the filter capacitors, they will cause the current draw to become out of range as you advance the variac you will notice the current goes up a lot if there is anything wrong. Be prepared to power off at once and mend the problem before subjecting another 80 to a premature end. All electrolytics and all wax capacitors must be replaced in old radios, no good foolproof way to test them has convinced me so yet.

Best!

[Phlogiston]

He is running the 80 (280) ouside of the chassis. No caps involved. He is attempting to activate the getter to absorb some gas. I would have just run it at 5 volts. But ther may be a reason to warm it up slowly.

[hsusmann]

Yes, I am running the 80 tube outside the radio
on a lab supply. So far I've run it a total of about
12 hrs and I already notice a difference in the color
of the glow.

It started out blue but now is violet.

I am going to run it for a few more days and then
go to full filament voltage and run it another few
days and see what happens.

Herb S.

[Phlogiston]

From my experiences, violet is worse than blue for indicating gas. Sill, interested in hearing how it comes out.

[hsusmann]

OK, that is interesting that violet is usually worse than blue.
When I apply reverse plate voltage on the tube with the
filament at full power I still don't get any reverse current
which sounds good to me.

Will post updates as this experiment goes on ...

Herb S.

[PAradiogeek]

I'm definitely not an expert, but the things that I've read say that a blue glow in a tube is not an indicator of a problem. See below:

http://www.rru.com/~meo/Guitar/Tubes/blue_glow.html

- and -

http://www.thetubestore.com/Resources/Ma.../Blue-Glow

Maybe you don't have a problem. Definitely interested in the general consensus though.

Jon

[jontz]

I'm with PAradiogeek. I'm very new to old radios, but not to tubes in general. I've seen many guitar amps tubes glow blue/violet that were perfectly fine. Perhaps that's not the case with these older tubes, and I'd love to learn if I am wrong. If the tube checks out OK and there aren't excessive grid currents, I think you are good to go.

[Phlogiston]

Once again, one of my favorite tube pictures -

This IS A BAD tube. If your glow is blue maybe not. Violet is bad.

   

[Ron Ramirez]

If there is a blue glowing spot just inside the glass but not within the tube's elements, your tube is probably OK.

If there is a violet glow within the tube's elements as Phlogiston's photo shows above, your tube is bad, period, end of story.

Note: Not applicable to gas-filled rectifiers or thyratrons.