Line-cord antenna coupler - safe on new cord?; tube substitutions

[radiotvnut]

Originally Posted by Jeffhs

I've never actually seen a phonograph with a one-tube amplifier, but I have heard of them. Never saw one with a single 50EH5, though. The one-tube phonos I've heard about have had a 117Z3 tube, wired in series with a 90-volt turntable motor. As I understand it, if the tube filament burns out in one of these, the motor will stop as well.

I would think there would have had to be at least two tubes in any phonograph that used a single 50EH5 as an amplifier stage, the second tube being a 35Z5, 35W4 or similar type rectifier (with a dropping resistor to take up the remaining 32 volts) unless, of course, a selenium power rectifier was used. Also, one other problem with one-tube phonos that used the 117Z3 could arise if the tube developed a heater-cathode short. Since the tube filament is connected directly across the AC line, such a short would blow a fuse or kick out the circuit breaker immediately upon turning the set on or even plugging it in (the switch need not be on), and could burn out the phonograph motor at the same time by virtue of putting the full line voltage across the 90-volt winding unless the circuit was fused. I doubt very seriously, however, if any of the one-tube phonos using line-operated tubes had line fuses, although goodness knows it would have been a good idea from a safety standpoint.

I know this is OT; but, I'll share my two cents on phonographs since you brought it up.

I've seen plenty of those record players from the '50's and '60's. Most of the mono units used a 25L6 tube in series with a 90 volt phono motor. The rectifier was usually selenium. Some of the later ones had a silicon rectifier. I've seen some stereo models that used two 60FX5 tubes in series. The main thing I dislike about these one tube record player's is that they require a high output cartridge (2 to 3 volts) to drive the tube. The better models used a lower output cartridge and had a preamp tube ahead of the output. The only portable record players I've seen with fuse protection were the classroom models (Califone, Newcomb, Audiotronics) and the "talking book" record players for the blind furnished by the library of congress. Some of those had a circuit breaker instead of a fuse.