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#1
03-13-2013, 08:46 AM
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Why no UHF converters with RF amp?
I was thinking about 50s UHF converters. I don't know of a single one that had a RF amplifier. Given the problems with UHF reception and the very poor noise figure of converters with no RF amps, why didn't at least one manufacturer make a premium model with an amp? They had the technology and it wouldn't have been terribly expensive.
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#2
03-13-2013, 09:14 AM
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I have to look at the schematic. It's really a complicated beast. Also, look at the tuner in the CT100. It's simular to the tuner in the all channel 1953 RCA, all channel sets. It sure is food for thought. 
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#3
03-13-2013, 09:20 AM
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The U70 has two IF amps, but no RF amp. The CT-100 doesn't have a UHF RF amp, and I don't know of any 50s tuner that had a UHF RF amp.
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#4
03-13-2013, 09:22 AM
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Excellent question
If I had to guess, I'd say that most 1950's-era converters were intended for little more than reception of low power UHF and translators serving a limited, line of sight radius. The Mallory I had was not very sensitive, often worse than a bult-in tuner. A few rocks between me and the Philly transmitters 45 miles away made it hard to get decent UHF without a rooftop antnenna AND a UHF mast-mount pre-amp. If you were one hilltop away from the UHF transmitter in the old days, you didn't count for being in the coverage area. In those days, a 500 kW UHF channel was unheard of. I have several Blonder Tongue converters from the 60s that seemed to work as good or better than a factory-installed UHF tuner. They still were hashy if there was a strong local UHF channel. 6AF4 was connected as an oscillator , using an 1N82A diode for a mixer, didn't a factory UHF tuner also lack the RF amp stage? All VHF tuners had a true RF amp, a stage of amplification between the antenna and mixer stage. This same stage was used to amplify only the IF output of the UHF tuner, after the noise was added, not very helpful. I have never seen a tube booster for UHF either. Last edited by DavGoodlin; 03-13-2013 at 09:28 AM.
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#5
03-13-2013, 09:26 AM
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Good point about tube boosters. I think that Jerrold made a mast mounted UHF amp for MATV use, but I'm not sure when it was introduced.
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#6
03-13-2013, 09:41 AM
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It had to be a cost factor, for the manufacturers. IIRC, amplifier tubes made for UHF frequencies were rather pricey. 
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#7
03-13-2013, 09:55 AM
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But surely there would have been a market for a high end converter?
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#9
03-13-2013, 12:44 PM
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Blonder-Tongue made two models, one with a single 6AF4 and a better model with a 6AF4 plus a 6AB4 as VHF "IF" amp outputting on Ch. 5 or 6.
We sold a jillion of both models back in the day in a deep fringe 'hole' served by translators. The received signal was always line-of-sight and strong enough to not need preamplification. Just guessing, but this was factored into the design of the converters, ie., they were never intended for UHF "DXing"
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#10
03-13-2013, 04:50 PM
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Quote:
http://www.ggninfo.com/May05.htm jr
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#11
03-13-2013, 05:40 PM
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Hi All;
I have a book from the early 50's, that has building instructions for both an RF Amp and a UHF converter.. It I think.. "78 Electronic Radio and TV projects".. It has a bunch of stuff.. By (I THINK) Popular Science.. THANK You Marty
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#12
03-13-2013, 08:35 PM
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Quote:
unintended harmonics that would show up as beat notes or moire on the TV screen. Again, just a guess. [Running for the deepest corner of the basement...]  Cliff
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#13
03-13-2013, 11:11 PM
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There's also an article from late '81 or early '82 in one of the Gernsback pubs. Really well thought-out-looking UHF RF amp for TV. I had a copy, long lost now. The author called the SMT parts "chip" capacitors and resistors. A UHF preamp is not something to hodge-podge together and expect it to work!
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#14
03-14-2013, 12:48 AM
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The first UHF converter designed for the Bridgeport CT UHF field trials in 1950 had an RF amp. It was a 6J4 triode in a grounded grid configuration. It was quite involved, an RF amp, input mixer/osc, two IF stages and an output osc/mixer to produce a 21Mc signal to the TV IF. The 1950 RCA Blue Book (pg 220) has a paper describing the converter. Don't know if that design was actually used in the field trial, as the convertor I have, dated 4/50, has the two IF and mixer/osc tubes but not the RF amp. The paper also mentions the UHF test converter used in the Washington DC field trial in 1948 as having an RF amplifier, but again the unit I have from that trial doesn't have an RF amplifier either. Chuck
__________________
www.myvintagetv.com Learn from the mistakes of others - You can't live long enough to make them all yourself.
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#15
03-14-2013, 08:33 AM
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If UHF had been part of the initial design, it might have had better tuners. But was added later, and obviously the VHF technology couldn't just be extended to UHF. And
it wasn't widespread at first, so a "quick fix" optional CONVERTER was added. No RF and no detent tuning. I do have a Standard Coil tuner that clicked individual UHF channels (with a 21 mc IF), it was really an eight channel UHF tuner with each continuous 10 channel section "clicked" approximately into individual channels. It took FCC regs to start getting better UHF tuners. Bruce Roe K9MQG
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