Up to a million watts of dissipation.
The external-anode tubes are a nuisance to cater for. The grids are fragile and the whole thing breaks if the cooling fails when there is some power (even the heater).
-- -TV
Yeah, big iron plate-modulated MF and HF AM transmitters (think Voice of America) used a modulator tube to vary the B+ on the Class C final amplifer. IIRC that improved the efficiency by about 2x compared with lower level modulation and linear amplification.
They often used the same tube as the modulator and the final, which makes perfect sense--the plate dissipation is very roughly the same, and the RF isn't all that much faster than the audio.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
My last tube circuit (circa 1989) had an 833A in it--I needed to control some HV grids in a charge drift experiment, and nothing else had the combination of voltage capability and low off-state capacitance. I even ran the grid off batteries!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
From Rate Training Manual NAVPERS 10087-C "Basic Electronics Volume 1", fourth edition as published by Dover Books, 1980:
For a very large transmitter T2 might be 10 feet high and weigh 10,000 lbs
IIRC, it was known as Heising modulation.
The Tek 519 scope was 1 GHz bandwidth, with no vertical amp and a distributed-deflection crt. It used one giant 2cx-sort of tube for the horizontal deflection drive. The scope was mainly used for photography of rare single events.
I have a tube.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Paradoxically, it makes more sense to do that with valves than with transistors. If you accept that high power dissipation is unavoidable, a valve runs at a much higher temperature and can be much smaller and lighter for a given dissipation than the equivalent in transistors and heat sinks. The volume of cooling air required is also less because it carries away the power at a higher temperature.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
They're a lot more forgiving of mistreatment, too, as long as you don't drop them on the floor. Transistors tend to survive that better--open or shorted outputs, not so much. :(
My experience in tuning high-powered SSPAs is in plasma applications rather than communications--it gets interesting because the real part of the load impedance changes by a good two orders of magnitude when the plasma strikes, but that doesn't happen until you've got a nice high voltage across the load.
Tube amps can take it, but SSPAs want to shut down on account of high VSWR, so the tuning problem gets much worse.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Am 04.06.20 um 22:14 schrieb Phil Hobbs:
When I was still at school and a freshly licensed ham, I asked Thomson-CSF for a data sheet of a 2C39-like tube. They sent me in addition a complete data book of their product line, including the Hyper-Vapotrons intended for large MW transmitters.
The Plate looked somehow like a hand granate, with the vapor that formed in the trenches shooting itself away from the tube.
The data book may be still somewhere in my basement. :-)
Gerhard
>
Pineapple or potato-masher? ;)
I'd be interested to see an English version if one exists.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I have no idea how they did that before JB Weld was introduced. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
pineapple
Short googling returned this:
<Could not find it at the should-be-there place, but found a Philips app note instead that belongs to the RF transformer thread.
Gerhard
I'd never heard the term, but a web search brings up screen-grid modulation examples, e.g. .
Plate modulation is different, because it doesn't require the final to be running in a linear mode. AM is inherently inefficient, but using a Class A linear amp for the final wastes at least 75% of the electrical power. Plate modulation only wastes half, which (if all you've got is tubes) makes it a huge win.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Misspoke. It was an 813A.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Yikes, 30 MW/m**2? That's going some--like an SC-70 running at 120 watts, which could come in handy. ;)
30e6 W/m * (2 mm)**2 = 120WCheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
20W
with
The last known company for custom high power modulation transformers was Peter Dahl, which has gone out of business. With so many AM and SW transmi tters being replaced with high efficiency solid state, their market dried u p. Their main product was replacmets for broadcasters, and they could often supply a new transformer within three days. Their quality was higher than the originals, and flatter frequency response. One downside to the modern A M transmitters is the ability to modulate almost down to DC. A local statio n runs commercials that have
I wonder how they turned all those setscrews. In a vacuum chamber? Just TDR the stuff?
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
If you have a tank circuit after the tube, you can run the tube in class AB, which has a higher efficacy.
The final tube can run in class C, with a high efficiency, but the question is how to generate the high audio power. This has now been done for decades with semiconductors and some digital methods.
For instance the Brown Boveri (now ABB) 500 kW HF or 600 kW MF transmitters from the 1980's used 32 floating power supplies in series feeding the plate. Depending of the instant audio waveform amplitude,
1-32 of these power supplies were actually activated, thus varying the plate voltage based on the audio waveform.
That's version of Class G, which will save some power, for sure.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
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