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G6Tanuki · 25th Jan 2020, 3:54 pm

I'm sure I recall reading a book from the early-1930s in which people working for Marconi offered designs for experimental multi-anode/multi-grid valves in balanced-modulators for use on the transatlantic long-wave radiotelephone system (which, of course, was one of the earliest applied uses of ISB) and later pre-WWII shortwave radiotelephone systems.

Yes, they also used the classic 'diode quad' approach (AT&T used this too in their early systems multiplexing loads of phonecalls onto a single coaxial cable) but it seems that the whole idea of active balanced-modulators/demodulators goes back quite a long time.

I've even got a circuit somewhere from a 1930s ARRL magazine which shows a pair of 6L6 valves used as a 'high level balanced modulator' [carrier to the control-grids, push-pull audio to the screen-grids, 400V on the anodes] directly feeding the antenna, to produce a few tens of Watts of DSB on 7MHz - an idea I'm somewhat tempted to recreate.

We had to wait a while before the likes of the 6BN6 and 7360 arrived.

25th Jan 2020, 3:54 pm	#16
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: "Double anode" triodes/tetrodes. I'm sure I recall reading a book from the early-1930s in which people working for Marconi offered designs for experimental multi-anode/multi-grid valves in balanced-modulators for use on the transatlantic long-wave radiotelephone system (which, of course, was one of the earliest applied uses of ISB) and later pre-WWII shortwave radiotelephone systems. Yes, they also used the classic 'diode quad' approach (AT&T used this too in their early systems multiplexing loads of phonecalls onto a single coaxial cable) but it seems that the whole idea of active balanced-modulators/demodulators goes back quite a long time. I've even got a circuit somewhere from a 1930s ARRL magazine which shows a pair of 6L6 valves used as a 'high level balanced modulator' [carrier to the control-grids, push-pull audio to the screen-grids, 400V on the anodes] directly feeding the antenna, to produce a few tens of Watts of DSB on 7MHz - an idea I'm somewhat tempted to recreate. We had to wait a while before the likes of the 6BN6 and 7360 arrived.