[Joeztech]

As a follow-up to the modification of the 1st IF from a 7H7 to a 6SG7, I did receive the new old stock Sylvania 6SG7 from AES on Friday. Yesterday I felt better after a Tylenol to help diminish the fever I was having from the flu and installed the new tube. A quick check with the substitute AM loop antenna showed that the reception is better than before with many more AM stations appearing all up and down the dial. So this particular tube is a good replacement (not substitute) for the original 7H7.

On another issue, the very slow warm-up, I note that after viewing several Philco schematics there are slight differences in how the output tubes are biased depending on whether they are 6K6GT or 6V6GT tubes. Here is a list I compiled of what I found:

46-1209 uses 6V6GT output tubes and a 150 ohm candohm resistor (no part number found for this one)

46-1226 Code 125 uses 6K6GT output tubes and a 265 ohm (measured) candohm resistor P/N 33-3435-7

47-1227 uses 6K6GT output tubes and a 165 ohm candohm resistor P/N 33-3435-1

47-1230 uses 6V6GT output tubes and a 135 ohm candohm resistor P/N 33-3435-2

So what I gather from the above information is that when Philco used a grid bias resistor that was higher resistance (producing slightly higher negative bias) when they used 6K6GT output tubes. When Philco used 6V6GT output tubes they used a lower value resistor and consequently less negative grid bias in order to turn on the 6V6GT tubes.

I know that this site has listings of the various Philco Block Capacitors by Philco P/N but is there a listing of values for Philco P/N candohm resistors?

I believe the candohm 33-3435-7 resistor that I find in this 46-1226 Code 125 radio should have been closer to 165 or 170 ohms. I think this particular candohm resistor has something wrong with it. The next step will be to find a suitable lower value of 150 ohms or 135 ohms to properly bias 6V6GT tubes. Otherwise if 6K6GT tubes are to continue to be used a 165 or 170 ohm resistor will be installed. Since I have two good 6V6GT tubes on hand and would have to order 6K6GT tubes I plan to install one of the lower values in place of the existing candohm resistor. I believe this will also correct the very slow to produce good audio problem. Other voltages are correct throughout the radio.

Joe