6A7 question on 39-6 - Printable Version
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6A7 question on 39-6 - Shaleradio - 07-21-2018
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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
RE: 6A7 question on 39-6 - Ron Ramirez - 07-21-2018
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.
RE: 6A7 question on 39-6 - Phlogiston - 07-21-2018
- - AND don't run it anymore. A GASSY tube like that one can arc.
RE: 6A7 question on 39-6 - Shaleradio - 07-21-2018
Thank you both! I was HOPING it was the tube, but I've never seen that before.
RE: 6A7 question on 39-6 - codefox1 - 07-23-2018
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.
RE: 6A7 question on 39-6 - Arran - 07-28-2018
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