The PHILCO Phorum

O[attachment=16844][attachment=16843]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

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.

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

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

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.

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