Tuesday, April 11, 2017
Stepping Inside an AM Transmitter (video)
Very cool video. We have visited VE7ZWZ's amazing shack before. This time he takes us inside a BIG commercial AM transmitter that he has modified for use on the amateur bands.
I know that he had the plate voltage turned off, but I still felt myself cringing when he reached up to touch the plate connectors on those enormous thermatrons. The filaments were on, adding to my unease. Dude, don't do that! And if you are standing INSIDE the transmitter, keeping one hand behind your back might not be as beneficial as it normally would be.
His comments on his VFO were interesting. I was kind of disappointed that he went with a varactor circuit. A varactor? Amidst all those bread slicer variable caps? It just doesn't seem right. (And BTW they are bread slicers, NOT "potato slicers.") But I kind of liked the heater--thermistor--insulation set up that keeps the VFO at constant temperature.
I thought it was interesting that these transmitters were kept on, with the tubes glowing for years at a time.
Thanks Mr. Carlson, for another great video!
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Nothing spectacular for this old duffer - except SCALE!. One gotcha though: referring to 6L6s as triodes. Sorry, they're (beam-power) pentodes. The series went like this: 6F6 signal pentode (may even have been a tetrode, I forget...) > 6V6 (beam-power, ~5W) pentode > 6L6, ~30W ... all intended for audio but serviceable to HF. UK names EF3? for the 6F6, EL3? for the pentodes (30-series Octal, there were equivalents in the 80-series B9G envelopes, including a double-6V6!). An early version of the 6V6 was the 'side-pin' socketed EL3N (Mullard). Gads, history! :) I had a side-pin superhet set that I rescued in High School: ECH3 triode-heptode converter, EF3 (?) IF, EBF2 detector/AGC+audio, EL3N output, AZ1 rectifier. Broadcast and short-wave 6-18mc/s (yep, that early!). That helped me immensely in my French studies - I could find Radio France each end of the dial. :)
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