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The most common radio to come out of the vacuum tube era was the All-American Five. Consisting of 5 tubes (thus the name,) the heater voltages of the tubes added up to 121 volts, and the radio could be operated directly from the AC line without a transformer - but could also be operated from a sufficient DC source as well as there was no power transformer.

Before that all happened, however, battery powered sets were popular. Several types of tubes were designed for this, all with low filament voltages that could be operated off common dry cell batteries. But that was expensive, and as the country became electrified, more people demanded sets that could run on wall current.

To meet this demand but still provide battery sets to those who wanted them, the 117Z3 was introduced. This tube performed as the DC power supply for a battery set when plugged in. Having a heater voltage of 117V, it didn't depend on any other part in the set to operate, but also didn't interfere when the set was used on battery.

It was created as a fix to allow manufacturers to keep making what the did without changing anything else, but as electricity came to most places, the need for battery sets faded, along with the parts created to make those sets work without batteries. Now, this tube is an oddball, but still useful, you can use it to provide B+ (high voltage for the plate) on tubes but run the rest of the tubes on a DC power supply to reduce hum and other artifacts of AC voltage.

The most common radio to come out of the vacuum tube era was the All-American Five. Consisting of 5 tubes (thus the name,) the heater voltages of the tubes added up to 121 volts, and the radio could be operated directly from the AC line without a transformer - but could also be operated from a sufficient DC source as well as there was no power transformer. Before that all happened, however, battery powered sets were popular. Several types of tubes were designed for this, all with low filament voltages that could be operated off common dry cell batteries. But that was expensive, and as the country became electrified, more people demanded sets that could run on wall current. To meet this demand but still provide battery sets to those who wanted them, the 117Z3 was introduced. This tube performed as the DC power supply for a battery set when plugged in. Having a heater voltage of 117V, it didn't depend on any other part in the set to operate, but also didn't interfere when the set was used on battery. It was created as a fix to allow manufacturers to keep making what the did without changing anything else, but as electricity came to most places, the need for battery sets faded, along with the parts created to make those sets work without batteries. Now, this tube is an oddball, but still useful, you can use it to provide B+ (high voltage for the plate) on tubes but run the rest of the tubes on a DC power supply to reduce hum and other artifacts of AC voltage.

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[–] [deleted] • 2 pts

I've messed around with tube amplifiers a little bit. Rebuilt a pair of st-60's and did a few mods to them during the rebuild. Ditched the solid state dc rectifiers someone converted them too and went to a pair of dual tube rectifiers on each. Haven't ventured too much into radios yet as I haven't had time but i've actually got a battery powered portable tube radio that was handed down to me and needs to have a good bit of restoration work done.

[–] • 2 pts

Yeah, solid state rectifiers can cause more problems than they solve in tube stuff. You get noise radiated from diodes that the amps can pick up (hash radiation,) and instant DC on the plate can cause cause a phenomenon known as cathode stripping which is exactly what it sounds like - the cathode isn't hot so the potential on the plate literally strips the cathode because it's not emitting.

As far as your radio, dig into it's history a bit as to make sure you aren't embarking on a project that can't be completed. I'd guess it's too old, but some radios suffer from problems like silver mica disease where the IF cans have silver-mica capacitors that break down over time.

[–] [deleted] • 2 pts

Yeah some of the tubes can be hard to find for sure and the new tube reproductions you find are never really as good as the old ones. They sound all right and work but they just don't last as long. One of the first things I do is go through and replace any electrolytic capacitors I find and I figure this radio ill need to go through and check capacitance on everything as well as redoing all the wiring because stuff this old it usually has fallen apart.

[–] • 2 pts

Well, too old for silver mica problems. Not too old to find parts, you can always sub similar tubes if one isn’t available.