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EL34 Blue GLow
EL34 Blue GLow
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Old 26th December 2002, 11:49 PM   #1
stigla is offline stigla  Norway
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Join Date: Nov 2001
Location: Trondheim
Default EL34 Blue GLow

Yeah, I know this have been asked before...

I've been breadboarding this guitaramplifier with 2 EL34's with a Marshall 50W replacement Transformer from Antuiqe Elec.

This is the first time I am dealing with pentodes, and the first thing striking my eyes when first powering up the amp, is a blue glow inside and between the electrodes of both the EL34's. I know this is a bad thing...

Thing is, the tubes are new, JJ's E34L's to be excact. I have triple-checked my wiring. Can't find anything wrong. I have a fixed bias supply and a separate one for each tube. They have about 450V@30mA to work with, and the glow appears at lower currents too...

The glow seems to be situated between the plate and the 3'rd grid, or maybe the 3'rd and the screen, hard to tell.

Is this my bad luck here? have I got 2 bad tubes just as a coincidence? Or is there some obvious wiring error that I cant see?


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Old 27th December 2002, 05:06 AM   #2
fdegrove is offline fdegrove  Europe
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Join Date: Aug 2002
Location: Belgium
Default ER 34 BRUE


I know this is a bad thing...
The heading is just a joke (one I experienced with Japanese customers asking for the Tesla E34L blue glass).

What you're experiencing though does not really constitute a bad thing.
With some new tubes you may see this blue glow due to execessive gaseous content in materials used.

The function of the getter is to burn this off and you will notice that this glow will lessen given time.

It will not affect the performance nor sound of that tube by any means so please don't panic.
Nothing is wrong with the tubes at hand.

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