[Shaleradio]

O         Got a 39-6 that was DOA.  After recapping and switching out resistors that read bad, it now comes on and the tubes light.  However, my 6A7 (Det-Osc) has me puzzled.  
Off of a dim bulb tester with a 65W bulb (39-6 requires 40w), the 6A7 is bright and the blue light will pulse along the grid section (see pix).  With a loop antenna, I can get a station when I touch the grid cap of tube 78 (IF).  My 6A7 reads are:  pin 2(plate) is 191v the schematic shows 145v.  Pin 3 (screens 3&5) read 122 and the schematic shows 75v.  Pin 4 (grid#2) is 192v and the schematic shows 145v.  On pin 1 which is my heater feed, I get 5.6vac and the spec sheet for the tube shows 6.3 v.  
I have a 6A7 on another working Philco but I'm afraid to switch it for fear my issue may not be the tube but something else.
I have no tube tester, just a multimeter.  Any suggestions?
Mark

[Ron Ramirez]

Anytime you have a tube with a purplish blue glow inside the elements as shown in your photo...the tube is bad. Replace it and try again.

[Phlogiston]

- - AND don't run it anymore. A GASSY tube like that one can arc.

[Shaleradio]

Thank you both! I was HOPING it was the tube, but I've never seen that before.

[codefox1]

Yes, tube is gassy and needs to be replaced. Purple glow OUTSIDE the elements within the bulb is not necessarily the end. I had a pair of 6L6's that danced to the music in an old amp and it plaed on for a while. But your tube needs to be changed.

[Arran]

Very pretty glow, but useless as a mixer oscillator tube, the gas disrupts the mutual conductance of the tube, making it conduct too well, almost like a short circuit. I've never seen that happen with a 6A7 tube before, I had a #224 tube that did that and had to get a refund from the fleabay seller I bought it from, but it was a balloon type so you run into that more often with early production tubes then later ones.
Regards
Arran