RadioBanter - View Single Post

June 17th 06, 06:46 PM posted to rec.audio.tubes,rec.radio.amateur.homebrew

wrote:
Pooh Bear wrote:

wrote:

Is this classic "gassy" tube failure? Towards the end it seemed to be
slightly more blueish on the top.

What condition was the getter in ?

Dark metallic. Not whitish, not even on the edges.

Just warmed it up again, and looked for interelement shorts. No shorts,
just lots of grid and plate current when negative grid bias and B+ is
applied, it seems to "run away" in fact (after 5-10 seconds of bias/B+
the currents start taking off steeply). No oscillations/parasitics on
the scope.

I actually have another GE 807 that's been in my junk box for many
years (presumed "junk"), and it has a similar getter and similar excess
currents (actually worse).

semi-dumb question: where are you measuring the bias voltage? (directly
at the tube, or on the other side of the grid resistor?)

I'm wondering if a bad coupling cap is causing the bias at the tube to
drift towards 0v or even positive.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com