CHRS West Coast Antique TV Event 5/18/24

[Tom Albrecht]

CHRS Antique TV Event

Date: Saturday, May 18, 2024

Time: 9:30 AM - 4:30 PM

Place: CHRS “Radio Central”, 2152 Central Avenue, Alameda, CA 94501

Our annual TV event returns again for 2024. The day's schedule will include presentations, demos, displays of working antique TVs, lunch, and plenty of time to hob-nob with fellow antique TV enthusiasts.

To get an idea of what this event is like, take a look at videos of our 2022 event here (last year our video recording didn't work out, although we had an equally nice event):

Part 1: https://www.youtube.com/watch?v=ZvpMQG4ABp8&t=12s

Part 2: https://www.youtube.com/watch?v=FpONMMRezcE

We're putting together this year's program now, and we will post updates here as plans come together.

The event is free of charge and open to both CHRS members and non-members. In past years we've had participants from Oregon, Nevada, and Southern California, as well as our locals from Northern California. If you're willing to travel to the Bay Area, you are welcome to attend. If you're not already on our email list and would like to be included, send me a PM for more details.

If you plan to attend, send me a PM so that we can plan for the right number of people. If you are interested in making a presentation or showing a technical demo, let me know.

[Tom Albrecht]

Our CHRS TV Event is just 4 weeks away on May 18. A nice schedule of presentations is coming together. Presentations will include:

1. The RCA CT-100 Was Not the First NTSC Color Set
2. Restoration of a Newly Acquired 1939 General Electric HM-185 Prewar Set
3. Early RCA Color Circuitry
4. Color Broadcast Programming in the Early Years
5. Showing of the "Real McCoys" Episode "The Television Set"
6. The Farnsworth GV-260 and the "Beam Relaxor" Horizontal Deflection Circuit

We still have room on the schedule for another presentation or two if you have something you'd like to share. Technical demos would also be most welcome, as are any sets you'd like to bring along to display, either working or static.

Lunch will be provided for a $5 donation. Let me know if you plan to attend so we can plan for the right amount of food. Hope to see you there!

[old_tv_nut]

Originally Posted by Tom Albrecht

Our CHRS TV Event is just 4 weeks away on May 18. A nice schedule of presentations is coming together. Presentations will include:

1. The RCA CT-100 Was Not the First NTSC Color Set
2. Restoration of a Newly Acquired 1939 General Electric HM-185 Prewar Set
3. Early RCA Color Circuitry
4. Color Broadcast Programming in the Early Years
5. Showing of the "Real McCoys" Episode "The Television Set"
6. The Farnsworth GV-260 and the "Beam Relaxor" Horizontal Deflection Circuit
...

The titles look really interesting - will the presentations be recorded for those who can't attend?

[Tom Albrecht]

Yes, the presentations will all be recorded, and I'll post a link to the video about a week after the event.

Last year we had a technical problem and we were not able to record the presentations on video. That was a real shame, since last year's presentations were especially good ones. This year we'll make sure that the video equipment is all working properly!

You can see the videos from 2 years ago at the link in the top post.

[Tom Albrecht]

The plan for the day has now been finalized for the CHRS Antique TV event:

Date: Saturday, May 18, 2024
Location: CHRS Radio Central, 2152 Central Avenue, Alameda, CA

9:30 - Early arrival for those presenting or displaying sets
10:00 - Welcome, introductions, and a few words about sets brought to display
10:30 - Early RCA Color Circuitry (Staples)
11:10 - 1946 Farnsworth GV-260 and the “Beam Relaxor” Horizontal Deflection Circuit (Albrecht)
11:50 - Lunch
1:00 - Showing of “Real McCoys” Episode “The Television Set” (Deal)
1:30 - Restoration of 1939 GE HM-185 Prewar Set (Albrecht/Pendleton)
2:10 - Coffee/Dessert Break
2:25 - RCA CT-100 Was Not the First NTSC Color Set (Staples)
3:05 - Early Color Programming (Pendleton)
3:45 - END

Presentations will be video recorded and made available to view after the event for those that can't attend.

In addition to the presentations noted above, we will also have the following sets on display:

1. Homebuilt 3 inch NRI school set (Dean)
2. Homebuilt 7 inch set (Dean)
3. GE HM-185 console prewar set (working); there is a presentation above on the restoration of this set (Pendleton)
4. Hallicrafters T-54 (working); related to "The Real McCoys" episode that will be shown (Albrecht)

Lunch and afternoon dessert will be provided for a $5 donation.

If you would still like to attend, but haven't let me know yet, please do so, so we can plan for the right amount of food.

[Tom Albrecht]

The video for this year's CHRS Antique TV Event is now available to view. If you were unable to attend and want to check it out, or even you were able to attend and simply want to review something, you can find the whole event here:

https://www.youtube.com/watch?v=hv-HC1jKDpk

Happy viewing!

[old_tv_nut]

Thanks, Tom!

[old_tv_nut]

I have added a question and two comments to the comment section of the video, including a copy of an extensive comment I originally posted on Videokarma about the rebirth and quick demise of I/Q demodulation in RCA's solid state sets, and the problems observed at Zenith when I did a thorough study of the issue. Basically, there was quadrature distortion produced by some color encoders that didn't suppress the lower Q sidebands enough - so some sources looked good and others had objectionable quadrature distortion on color edges. (All the professional encoders met NTSC/FCC specs - the NTSC just never realized they needed tighter specs, and you couldn't see the effects on a 15GP22.) Zenith engineering management would not accept that sometimes the picture would look worse than others. RCA reduced the quadrature effects by reducing the amplitude of the I-channel high frequencies to where they did very little to improve color resolution.

[Tom Albrecht]

I brought your comment from the YouTube page over here, since John Staples has a reply which I can also post, which might possibly generate some further discussion. Probably easier to do that here than on YouTube comments.

Your comment regarding the Westinghouse color TV use of a non-crystal controlled oscillator to track the chroma bursts:

"Regarding the Westinghouse crystal-less color oscillator: The main reason for using a color crystal VCO and not an LC is that the crystal can be guaranteed not to drift so far (actually much less than one-half the horizontal rate), so that side lock to the burst is impossible, even in a home set without a crystal oven to control the temperature. An LC oscillator could be tuned off frequency by a multiple of horizontal, in which case the hue would go through a stable rainbow pattern (or multiple rainbows) from left to right. So, the Westinghouse circuit required an unusually stable LC oscillator that would drift very little even when in the hot chassis environment."

John's response (via email to me earlier today):

"Thanks for the first comment which add some more information about how the different bandwidths of the I and Q signals are handled.

"The second comment is very interesting as it may shed some light on what the APC circuit is. The point is that the Hartley oscillator may lock on to a frequency that differs by the horizontal frequency or something else and would give a rainbow.

"Here is the schematic of that circuit which I should have included in my talk, although it is almost unreadable.

"Note the usual upper 6AL5 phase detector in the PLL, but also note the lower phase detector excited at 90 degrees which feeds the color killer, which I spoke about, but also an additional low-frequency coupled loop through the 12AX7 back to the reactance tube. This may be a way to detect that the Hartley oscillator is locked by some multiple of the horizontal frequency off, and a beat note may kick the oscillator back on frequency. Just a speculation.

"What do you think?"

[old_tv_nut]

My first thought was "is this a frequency detector?"

A circuit called the DC quadricorrelator was invented by Donald Richman that added a third phase detector whose inputs were the output of the normal phase detector and a differentiated output of the color killer detector. Since the output beat notes of the first two detectors are are 90 degrees apart, but the diffentiator shifts one of them, this third detector produces a signal proportional to frequency offset. This speeds up the acquision of the phase lock loop, but cannot solve the side lock problem.

The Westinghouse circuit lacks the third detector. I will look at it further, but I suspect it has something to do with speeding up the acquisition when the oscillator starts far away from nominal frequency (but still not so far as to permit side-lock). Again, a crystal oscillator can be guaranteed not to start so far off from nominal as an LC oscillator might.

Wish I could see the component values more clearly.

[old_tv_nut]

Note that the ordinary phase-locked loop develops a DC pull-in voltage when initially off FREQUENCY (not only phase) because the beat frequency is low enough to pass to the control device and therefore causes the frequency variation vs. time of the oscillator to be non-sinusoidal, thereby developing a phase error voltage in the detector that is present longer in one polarity than the other. However, since the control voltage has to be low pass filtered, this asymmetry is greatest when the frequency difference is small, and gets less and less for greater frequency offset (and higher beat frequency). If the beat frequency is too high to pass through the low pass filter to the control device, the loop will fail to pull in. This odd circuit may be amplifying the higher AC beat frequencies to wobble the oscillator more strongly when the offset is large.

Time to sleep on this and I'll take a closer look tomorrow.

[old_tv_nut]

The 12AX7 cathode follower gets its input from the phase detector through an RC highpass (0.1 uF and 220k). Cutoff would be 7 Hz (probably modified by other things hanging on the phase detector output).

The phase detector lowpass filter (reading from the 15 inch receiver schematic) appears to have a very low first break point with a 4 uF and 104.7 K = 0.4 Hz, then attenuation shelf of 20x out to a final rolloff of 318 Hz. (The corresponding rolloff points on a CT100 apear to be 29 Hz and 1592 Hz.)

In the modified circuit, the 4 uF seems to be missing, and I'd guess its rolloff is replaced by the coupling capacitors from the 12AX7, but I can't read their values, nor the resistor that goes from the common point of the two electolytics to ground.

Summary thought so far: the 12AX7 serves to increase AC coupling above 7 Hz. Still, I'm puzzled as I don't see any provision to roll off its effect at higher frequencies - it seems like this circuit would swamp the effect of the 100k and 5000 pF regular filter. I would have thought therre should be a resistor in series with the connection from the 12AX7 and the test point, just like the resistor in series with the 4 uF in the unmodified circuit.

Maybe someone else can work their way through this to see what it's actually doing.

[ChrisW6ATV]

Thank you for posting the video link, Tom, and for your work to make the event happen.

[Electronic M]

Old_tv_nut the early television museum has both the factory service literature and Sam's for the westinghouse that are probably more legible. http://earlytelevision.org/pdf/westi...ms_0259-15.pdf

[old_tv_nut]

Originally Posted by Electronic M

Old_tv_nut the early television museum has both the factory service literature and Sam's for the westinghouse that are probably more legible. http://earlytelevision.org/pdf/westi...ms_0259-15.pdf

Yes, but do they have something with this modified circuit?