03-12-2015, 07:31 PM
It's alive. Sort of.
[Image: http://www.philcoradio.com/images/phorum...5T_032.jpg]
I tested all of the tubes. The 84 was OK, surprisingly. The 41E was slightly weak as was the 78E. The 75 was significantly weak and was replaced. The 6J8EG tests very weak also, but I don't have any spare 6J8EG tubes.
So I tried the set out anyway.
Result: I had no trouble picking up my SSTRAN at 660 kc, but I had to turn the volume way up to hear it. And the audio is somewhat low and distorted.
Then I noticed the screen grid of the 41E was glowing red - not a good thing.
I took some voltage readings with my DMM and noticed that all DC voltages are running around 30 volts higher than the Philco data indicates. But that does not surprise me, considering the 1000 ohm/volt meters used in ye olden days which loaded down the circuit under test...combined with today's higher line voltages.
I checked the specs of the 6K6GT (octal version of the 41) and it indicates a maximum plate voltage of 315V, maximum screen voltage 285. The voltage readins I obtained were below those levels - not a lot lower on the screen grid, but lower. So I don't think the 275 or so volts (I say "or so" because the reading kept fluctuating) on the screen is what is causing it to glow red.
Tomorrow I'll try a different 41 tube and try it again. I'll also double-check my wiring, but so far it looks OK.
-----
As is typical with Philco, they run the screen voltage of the output tube higher than the plate voltage. I am considering adding a series resistor to drop the screen voltage to a level at or just below the plate voltage. Looks like a 1 watt, 2700 ohm resistor would do the trick. The only problem is, I would have to add a terminal strip near the 41 tube's screen grid pin owing to the way the set is wired. It may be more trouble than it's worth pursuing.
[Image: http://www.philcoradio.com/images/phorum...5T_032.jpg]
I tested all of the tubes. The 84 was OK, surprisingly. The 41E was slightly weak as was the 78E. The 75 was significantly weak and was replaced. The 6J8EG tests very weak also, but I don't have any spare 6J8EG tubes.
So I tried the set out anyway.
Result: I had no trouble picking up my SSTRAN at 660 kc, but I had to turn the volume way up to hear it. And the audio is somewhat low and distorted.
Then I noticed the screen grid of the 41E was glowing red - not a good thing.
I took some voltage readings with my DMM and noticed that all DC voltages are running around 30 volts higher than the Philco data indicates. But that does not surprise me, considering the 1000 ohm/volt meters used in ye olden days which loaded down the circuit under test...combined with today's higher line voltages.
I checked the specs of the 6K6GT (octal version of the 41) and it indicates a maximum plate voltage of 315V, maximum screen voltage 285. The voltage readins I obtained were below those levels - not a lot lower on the screen grid, but lower. So I don't think the 275 or so volts (I say "or so" because the reading kept fluctuating) on the screen is what is causing it to glow red.
Tomorrow I'll try a different 41 tube and try it again. I'll also double-check my wiring, but so far it looks OK.
-----
As is typical with Philco, they run the screen voltage of the output tube higher than the plate voltage. I am considering adding a series resistor to drop the screen voltage to a level at or just below the plate voltage. Looks like a 1 watt, 2700 ohm resistor would do the trick. The only problem is, I would have to add a terminal strip near the 41 tube's screen grid pin owing to the way the set is wired. It may be more trouble than it's worth pursuing.
--
Ron Ramirez
Ferdinand IN
