Single ended tabletop radios.

[Big Bean]

Remember the wood cased Zenith tabletop radios from the fifties and early sixties. It's my understanding that many of them were single ended, can anybody confirm this? Thanks.

[boom3]

I have a Zenith AM-FM table radio from 1960, although the circuit design is the same as models from at least 1951 onwards. The audio output is a 35ZGT operating single-ended. (I may have blown the exact number, but it is a 35 series tube) I think a pentode. This was very common since most of these sets were "series heater string" designs that had no power transformer. The heaters of all the tubes were in series, and the voltage drops equal 110 volts, more or less. My Zenith heater string only equals 102 volts, but I'm sure that the selenium rectifier's drop and other losses mean that no heater is overstressed. I think these used a siimple voltage doubler to get B plus which would be no higher than 240-250 volts for these tubes anyway.

Trust me, the single-ended approach for these and competetive radios had nothing to do with fidelity, it was all about reducing the parts count and keeping to target cost.