11-19-2012, 01:34 PM
Yes, quite a few 6J5G tubes. This has become more of an issue with the event of the 6J5G going up in price. IF you use the cheaper 6J5GT or MG tubes you must "modify" the tube shield base. In a cinch, you can use a 6C5G tube to replace the 6J5G, but the 6C5G has a lower mmho rating.
The AF section of the 37-670 employs four 6J5G tubes (1st Audio, Phase Inverter, and PP Drivers) to drive the PP 6F6G output tubes. If you consider the mutual conductance of just the 1st Audio and PP Drivers, you have a very favorable comparison to that of the late-model 116B, which incorporates a 77 tube 1st Audio and 42 tube driver.
This makes me wonder if Philco opted for more in the AF side of the design of the 37-670 vice an additional IF circuit.
Looking at some other schematics from the 37 model year, I noted that the only sets with two IF circuits were the 37-116, 37-675, and 37-690. Philco DID add an extra AF amplifier (6J5G) to the 37-660 set, but interesting to note that the 37-665 (same # tubes as the 660) had one AF amp/driver (6K6G) and added a separate 6J5G oscillator tube and used the 6A8G for a detector only. The 37-660 combined the Oscillator/1st Detector in the 6A8G tube.
Go figure...
The AF section of the 37-670 employs four 6J5G tubes (1st Audio, Phase Inverter, and PP Drivers) to drive the PP 6F6G output tubes. If you consider the mutual conductance of just the 1st Audio and PP Drivers, you have a very favorable comparison to that of the late-model 116B, which incorporates a 77 tube 1st Audio and 42 tube driver.
This makes me wonder if Philco opted for more in the AF side of the design of the 37-670 vice an additional IF circuit.
Looking at some other schematics from the 37 model year, I noted that the only sets with two IF circuits were the 37-116, 37-675, and 37-690. Philco DID add an extra AF amplifier (6J5G) to the 37-660 set, but interesting to note that the 37-665 (same # tubes as the 660) had one AF amp/driver (6K6G) and added a separate 6J5G oscillator tube and used the 6A8G for a detector only. The 37-660 combined the Oscillator/1st Detector in the 6A8G tube.
Go figure...
