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 Post subject: NTSC Aural transmitter power reduced
PostPosted: Jan Sun 29, 2017 2:27 am 
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I am not sure if this should be here or in the clubhouse. Feel free to move it. Sometime between 1954 and 1969, the FCC either allowed or required television stations to reduce aural carrier power. I THINK this was sometime in the late 1950's, but it was before my time. RCA had a method for the TT-50 television transmitter which involved disconnecting one of the parallel final power amplifier tubes. Does anyone know when this was done? Thanks, Jim


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Jan Tue 31, 2017 3:30 am 
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The most recent discussion on this question can be found here:

http://antiqueradios.com/forums/viewtopic.php?f=3&t=312251

Nobody offered a specific date, something everyone involved would like to know.


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Jan Tue 31, 2017 5:46 pm 
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That is the discussion that started me thinking about the transmitter modification to reduce aural power. All my friends who were around back then and involved in such things are deceased. I was the kid.


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Jan Tue 31, 2017 10:52 pm 
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Likewise. My dad would have known. It was before my time too. It surely must be in books somewhere. Issues of Radio & TV news seem like a good place to start.


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Feb Wed 01, 2017 5:44 pm 
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I have been checking old magazines with no luck. I did get a clue from one magazine that it may have been after 1961.


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Feb Wed 01, 2017 11:34 pm 
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Radio and TV News might not be the best magazine to get that info. I'd try Broadcast News or one of its predecessors that catered to the broadcasters specifically. IIRC, they published FCC notifications and the like pretty regularly. The Library of Congress or FCC archives would be likely sources too, though they might be harder to slog through.

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A collector of TV signal boosters and UHF converters -- God help me!
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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Feb Fri 03, 2017 9:49 am 
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Greetings, All!

I went to a friend (Burt W.) who has spent virtually his entire adult life as a broadcast engineer, and he went to an old-timer he knows. His name is Donald Wilson, K6DSW. Here is his reply to Burt in full:

Quote:
This is from my memory, mainly based on references, and some experience.

There were several, separate aural power reductions.

Before NTSC color TV was adopted, the rules allowed aural power between 50% and 100%
of the peak visual power. The FCC color rules were effective in December 1953, in those rules
or soon thereafter, the aural power was reduced to between 50% and 70%.

By about 1956, as part of rule changes to make UHF TV more viable, UHF stations could
use aural powers between 10% and 70%, VHF stations still had a 50% minimum.

The change you were thinking of occurred about 1965. The maximum allowable aural power
for all TV stations was reduced to 20% of peak visual. Both VHF and UHF stations were required
to hold their aural powers between 10% and 20%. The 20% aural power maximum made proper
fine tuning of a color set easier and simplified the design of color receivers. On many sets, color
or black and white, adjacent channel interference was reduced, but that was not the reason for
the change.

There was one more change. In 1985 as part of a relaxation of technical rules, the minimum
10% power limit was eliminated.


In the mid 1960's, RCA supplied kits to reduce the aural power of many of their transmitters.

Many stations running the TT-50AH high band transmitters bypassed the aural final amplifiers.
The aural output from the 10kW driver could produce 7 kW.

The RCA 25 kW amplifiers (7 parallel 5762 tubes), used in the TT-25BL, and several other models
from the 1950's, were capable of 100% aural power. Since this was not usually needed, a station
could remove filament power from two of the aural final tubes and still be able to operate at 70%
aural power. The two tubes had to stay in the amplifier so that it would tune properly.

Donald Wilson
K6DSW




That's probably as close as you are going to get.

Regards,

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Jim T.
KB6GM


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Feb Fri 03, 2017 4:45 pm 
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Better than we expected. Thanks for your help.

Makes sense that color would have had an impact. People kept their TVs maintained back then, and in 1953 probably 95%+ of first generation sets were still in action, and subject to the semi-annual house call. Repairmen undoubtedly evolved methods to counter the effect of the changes in aural power over the decades. The bridged tube in Lee's 8TS30 being one such example.

Good research. Relay our thanks back to the "old timer" for his recollections, if possible.


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Feb Fri 03, 2017 8:30 pm 
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Thanks Jim and thanks to Burt and Don. You are completely correct, the mid 1960s kit is what I was really courious about. I recall reading the instructions for installation of that kit many years ago with only slight interest. Jim


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Feb Fri 03, 2017 11:56 pm 
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I imagine that sets built with two separate IFs (one video, the other sound) would have some difficulty with reduced aural carrier strength. Intercarrier sets less so. More often than not, the sound would come in better on weak stations than the video did.

UHF stations transmitting around a million watts would see a lower electric bill with reduced aural power. Which is not insignificant at that power level.


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Feb Mon 06, 2017 11:09 pm 
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wa2ise wrote:
UHF stations transmitting around a million watts would see a lower electric bill with reduced aural power. Which is not insignificant at that power level.


In practice, the "million watt" stations were using 100KW-class transmitters and gain antennas for a 1 million Watt "Effective Radiated Power" (E.R.P.). Still a pretty good reduction of those stations' AC power bills.

RCA's biggest UHF TV transmitters in the '60s were the TTU-110 series (two TTU-55's in parallel). I was a co-op at RCA in Meadowlands PA in the late 1960s, where those transmitters (and all RCA broadcast transmitters were made).

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Mark Nelson
A collector of TV signal boosters and UHF converters -- God help me!
tv-boxes.com


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Apr Wed 05, 2017 10:55 pm 
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I worked in TV broadcast in the late 50's and still do today

I don't recall the exact year but TV stations were allowed to reduce Aural power to 10% of visual where it remained until 2009 when we shut it off.

Before that it was 20%.

I believe this caused problems in the late 40's TV's especially if they weren't inter-carrier sound.

Now it doesn't matter because they are all gone.

Jim


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Apr Thu 06, 2017 12:17 am 
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Well, in a way it does matter. If the digital converter boxes and other modulators adhere to the 10% sound carrier level, then the old split sound set will still have problems because of that change.

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Tom


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 Post subject: Re: NTSC Aural transmitter power reduced
PostPosted: Apr Thu 06, 2017 1:39 am 
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Location: Phoenix, Arizona
Actually it doesn't matter :)

I have not looked a various set-top converters with a spectrum analyzer so I don't know what the ratio actually is.

When the FCC set up specs for set-top converters there was a lot of attention paid to receiver compliance but very little for the analog side.

In a word they didn't give a RAT because it was all expected to hit the landfill soon.

The converter I use to watch Meet the Press on Sunday morning drives my RCA 621TS which is a separate sound design and it seems to work OK.

I have a VHF transmitter modulator (exciter) I use to drive my house cable and it works good but I have the Aural up toward 20%

The bigger problem is Macrovision which I take out with an old grass valley 640 proc amp.

The new all-exciting digital, audio is of course in the stream and you can't adjust until you get your hand on the knob.

Analog audio is/was FM, Visual was/is AM, so the power ratio doesn't really matter now.

Jim


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