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  #136  
Old 11-14-2017, 06:37 PM
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  #137  
Old 11-15-2017, 11:34 AM
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Originally Posted by benman94 View Post
Regarding the correct 25 kV ultor voltage, see this quote from the RCA booklet entitled "Technical Features of the RCA Victor Model 21-CT-55 Color Television Receiver":



(Emphasis added by yours truly.)

I'm still failing to see what is ambiguous about the RCA specified ultor voltage, but to be honest I really don't care any more... I tried to help, I only hope you correct the issue before your flyback goes up in smoke.

Anyway, here is the factory service data you asked for "1954 No. T13", published November of 1954: http://docdro.id/HBjbl9P

You'll note that the only 3.3 MOhm resistor is in the grid circuit of the triode section of the 6AN8 that serves as the R-Y amp and phase splitter. I'm not sure what resistor Mike replaced in the 6BD4A circuit with two 2.2 MOhm resistors in series. Apparently he's smarter than RCA's own engineers. I guess we should all defer to some random guy with a soldering iron instead of the factory service literature...
From 1954......hmm... do you have the 13 Goldenrods (service Bulletins) issued against the 21CT55? (I don't either...) The last one was issued in 1972....and probably a parts stoppage report. Many of these Goldenrods were safety issues - without them, the original service literature is a snapshot in time.

By 1978 (when we got our first RCA service library, from RCA, 28 binders, TV only...), some 600+ Goldenrods had been issued by RCA for televisions. Some were minor part number changes, but in the case of ALL early color (CTC17 and earlier), RCA issued Goldenrods to limit the 2nd anode voltage in all sets to a value that reflected the amount of shielding around the regulator tube.

I'm not Chicken Little, crying about the X-rays - I'm merely pointing out that the original service lit has been revised many, many times and some original statements and values rescinded.

RCAman, a frequent poster, may still have an RCA library with the Goldenrods. Ours went the way of another shop when we closed up in 2008. They tossed all the tube stuff - I rescued what they still had - CTC72 and up, unfortunately.

Nick/Miniman82 - same as any NAVAIR pub change - remove the old stuff and put in the new, up-to-date stuff. Old values/procedures and part numbers no longer apply...
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  #138  
Old 11-15-2017, 12:08 PM
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Gonna have to disagree with the pub analogy, in this case I know better than to put unnecessary electrical strain on 60 year old parts. Besides, we’ve both been around long enough to see a pub or two with bullsh!t procedures in it.
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  #139  
Old 11-15-2017, 12:36 PM
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These sets were in service for around a decade when the X-Ray alarmists got started...A pre X-ray scare HV reduction I'd buy as merited, but any X-ray scare reductions I'd regard as superfluous and 'not running the set as it would have been during most of it's intended service life'. I rather see a CTC-2/CTC-2B doing what it would have done in the 1954-1963 time frame, than what it would do in 1967-1975.
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  #140  
Old 11-15-2017, 12:53 PM
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Quote:
Originally Posted by Electronic M View Post
These sets were in service for around a decade when the X-Ray alarmists got started...A pre X-ray scare HV reduction I'd buy as merited, but any X-ray scare reductions I'd regard as superfluous and 'not running the set as it would have been during most of it's intended service life'. I rather see a CTC-2/CTC-2B doing what it would have done in the 1954-1963 time frame, than what it would do in 1967-1975.
Agreed. As mentioned previously, the X-ray scare was completely unwarranted. Stick a 6EL4A in the set if you're that worried about it and call it a day. The X-rays are soft and the dose from a 21AXP22 face at 25 kV, or a shunt reg at 25 kV, is going to be negligible. I work with Coolidge tubes all day long. Trust me, if there were any real risks from a CRT I'd be the first to chicken little... You're more likely to be electrocuted by your CTC-2B.

I still have yet to see a logical reason to run this set at less than 25 kV, but plenty to run it at spec...

But if you don't believe me, defer instead to John Yurkon, a physicist as well, who has done actual testing on CRTs:

http://www.videokarma.org/showthread.php?t=112954
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  #141  
Old 11-15-2017, 02:32 PM
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Quote:
Originally Posted by Findm-Keepm View Post
From 1954......hmm... do you have the 13 Goldenrods (service Bulletins) issued against the 21CT55? (I don't either...) The last one was issued in 1972....and probably a parts stoppage report. Many of these Goldenrods were safety issues - without them, the original service literature is a snapshot in time.

By 1978 (when we got our first RCA service library, from RCA, 28 binders, TV only...), some 600+ Goldenrods had been issued by RCA for televisions. Some were minor part number changes, but in the case of ALL early color (CTC17 and earlier), RCA issued Goldenrods to limit the 2nd anode voltage in all sets to a value that reflected the amount of shielding around the regulator tube.

I'm not Chicken Little, crying about the X-rays - I'm merely pointing out that the original service lit has been revised many, many times and some original statements and values rescinded.

RCAman, a frequent poster, may still have an RCA library with the Goldenrods. Ours went the way of another shop when we closed up in 2008. They tossed all the tube stuff - I rescued what they still had - CTC72 and up, unfortunately.

Nick/Miniman82 - same as any NAVAIR pub change - remove the old stuff and put in the new, up-to-date stuff. Old values/procedures and part numbers no longer apply...
Interesting. So RCA issued “Adendums” / Goldenrods to update service data. I wonder if Mike has those for the 21CT55?
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  #142  
Old 11-15-2017, 02:46 PM
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I see that on pages 6 and 17 of the T13, RCA calls for setting the ultra voltage at 25KV.

What I’m trying to understand is how does this relates.

In the RCA data sheet for the 21AXP22A,

RCA states: max 25KV ultor voltage.

RCA states: equipment design range with any ultra voltage 20 to 25KV.

Look I’m not a tech, my 41 year career after the Navy was real estate law. Just trying to understand.

I remember Mike telling me that the Sams procedure for alignment was incorrect, don’t remember the specifics. This would not be the first time service manual’s are incorrect.
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  #143  
Old 11-15-2017, 03:16 PM
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Marshall,

Look again at the arrow in the datasheet you posted. The words "Design Center" are key here. The design center system of maximum ratings means it is completely safe to run the maximum allowed value. Design center means you can actually exceed the maximum value listed by about 10 to 20 percent, and provides a built in safety margin for parts value variation, manufacturing tolerances in parts, etc
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  #144  
Old 11-15-2017, 03:24 PM
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Look at this datasheet for the 15HP22: https://frank.pocnet.net/sheets/084/1/15HP22.pdf

CBS ran them at 20 kV ultor voltage.

Look at this datasheet for the 15GP22:
https://frank.pocnet.net/sheets/093/1/15GP22.pdf

Every manufacturer ran them at 20 kV (19.5 kV in the case of RCA, which is a negligible difference).

Look at this datasheet for the 10FP4 CRT. Most 10 inch sets ran them right at 10 kV or damn close to it.

https://frank.pocnet.net/sheets/201/1/10FP4.pdf

Do you see the pattern. Running at design center maximum is perfectly fine, and in the case of a CRT, often desirable.
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  #145  
Old 11-15-2017, 04:00 PM
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Your last two posts took the words out of my mouth before I could write them, Ben.


To add to your running at design center max being desirable. Most manufactures tried to do that for a couple of reasons: Brighter picture, and CRT life. The cathode material of a CRT has a somewhat finite number of electrons it can emit before the emissive material is depleted. The higher the HV the less gun current is needed for a given brightness setting, the less current the fewer electrons needed from the cathode for the same result, the fewer electrons used for desired result the longer the CRT life.

Also I'm not trying to knock your tech, but I remember you quoted your tech as saying that the HV regulator "shunts the excessive voltage" which conceptually is wrong. The regulator shunts current not voltage from the HV line to ground. You see every power supply has to obey the laws of Thévenin...That is there is no ideal voltage source. Every voltage source has an internal resistance, and that internal resistance forms a voltage divider with the load (CRT+HV reg tube). In the case of varying loads (such as a CRT) the output voltage varies as a function of load current drawn through internal supply Thévenin resistance. The HV reg is configured to attempt to increase it's relative current draw instep with decreases in CRT current draw (caused by video content), and decrease when the CRT increases. If the current through a Thévenin resistance is held constant (which is what the HV reg tube is meant to do) then the output voltage of the supply is also held constant.

There is also an average current to the HV reg that is adjusted by the HV level pot....The lower you set the HV level the higher the constant/average current (sum of CRT and HV reg tube) is on the HV winding of the flyback. The Thévenin resistance lives in the fly windings in the case of a TV like this, and thus the higher the HV current you put through it the higher the heat and strain on the flyback.

Many RCA flybacks were being pushed hard by design, adding to it does not strike me as desirable.
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Last edited by Electronic M; 11-15-2017 at 04:03 PM. Reason: typo
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  #146  
Old 11-15-2017, 04:32 PM
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Quote:
Originally Posted by Electronic M View Post
Your last two posts took the words out of my mouth before I could write them, Ben.


To add to your running at design center max being desirable. Most manufactures tried to do that for a couple of reasons: Brighter picture, and CRT life. The cathode material of a CRT has a somewhat finite number of electrons it can emit before the emissive material is depleted. The higher the HV the less gun current is needed for a given brightness setting, the less current the fewer electrons needed from the cathode for the same result, the fewer electrons used for desired result the longer the CRT life.

Also I'm not trying to knock your tech, but I remember you quoted your tech as saying that the HV regulator "shunts the excessive voltage" which conceptually is wrong. The regulator shunts current not voltage from the HV line to ground. You see every power supply has to obey the laws of Thévenin...That is there is no ideal voltage source. Every voltage source has an internal resistance, and that internal resistance forms a voltage divider with the load (CRT+HV reg tube). In the case of varying loads (such as a CRT) the output voltage varies as a function of load current drawn through internal supply Thévenin resistance. The HV reg is configured to attempt to increase it's relative current draw instep with decreases in CRT current draw (caused by video content), and decrease when the CRT increases. If the current through a Thévenin resistance is held constant (which is what the HV reg tube is meant to do) then the output voltage of the supply is also held constant.

There is also an average current to the HV reg that is adjusted by the HV level pot....The lower you set the HV level the higher the constant/average current (sum of CRT and HV reg tube) is on the HV winding of the flyback. The Thévenin resistance lives in the fly windings in the case of a TV like this, and thus the higher the HV current you put through it the higher the heat and strain on the flyback.

Many RCA flybacks were being pushed hard by design, adding to it does not strike me as desirable.
I hadn't even considered the lower cathode current. That's a good point Tom. The major issue that RCA was driving at was inefficient phosphors coupled with the shadow mask design.

The primary issue is that the red phosphor was extremely inefficient. The underlying physical process of exciting a phosphor is more efficient with higher energy electrons, which in turn demands higher anode voltage.

Side bar: This is the reason that many Zenith Walton owners have resorted to connecting the B+ for the eye tube (the rare Zenith specific one, 6T5 maybe?) with 500+ volts from a solid state source hidden in the set. With a burned P1 Willemite phosphor, that 500+ volts can bring back sufficient brightness. The cathodes in these tubes are usually still quite strong.

Also keep in mind that the shadow mask blocks a vast majority of the electrons leaving the cathodes. They simply strike the shadow mask and return through the HV lead back to the chassis, never striking a phosphor and therefore never producing light. This is why the Lawrence Tube, the Apple tube, the Sony Chromatron and Trinitron, etc were explored.

RCA took a different approch. Modify the existing shadow mask design to a degree and develop newer brighter more efficient phosphors. This of course culminated with the rare earth types.

Another note about design center: one of the biggest variables in those days was the line voltage. It could range from 105 V to 120 V at the outlet. In most places this issue has been corrected, and the tolerance is nearer to 120 +/- 5% at the service drop to the house. This variability circa 1954 caused proportional shifts in filament voltage and B+.

If you're one of the unlucky folks that lives at the end of a rural circuit serviced by DTE or Consumers, the situation hasn't changed at all since 1954...
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  #147  
Old 11-15-2017, 05:16 PM
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Good information flowing ...

Just read a 1954 paper by RCA last night. This particular tubes shadow mask, 21AXP22 blocks 85% of the electrons. This same figure was presented to the IEEE in a paper entitled “THE PDF CHROMATRON-A SINGLE OR MULTI-GUN TRI-COLOR CATHODE-RAY TUBE by Robert Dressler from the PROCEEDINGS OF THE I.R.E. VOL.41, NO. 7, JULY, 1953”, priniple engineer at Chromatic Television Laboratories’s Inc., developers of the Chromatron tube. The slot mask was an effort by American manufactures to increase the electron flow to the phosphors.

Like I said previously, I’m taking everything said seriously. We will curtail running the 21AXP22 until I have a chance to sort all of this out with Mike. He is about to have a second surgery and don’t want to bother him.

Any comments about the latest screenshots after the slug was adjusted?
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  #148  
Old 11-15-2017, 05:22 PM
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Originally Posted by etype2 View Post
Just read a 1954 paper by RCA last night. This particular tubes shadow mask, 21AXP22 blocks 85% of the electrons. This same figure was presented to the IEEE....
And this is exactly what I referred to in my last post. This is yet another reason why you run the jug at 25 kV...

As far as the screenshots go, I can tell, especially in comparison to the CTC-7, that the image is on the dim side. Otherwise they look alright.
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  #149  
Old 11-17-2017, 02:00 AM
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21CT55 Slideshow

See the slideshow at the bottom of this link page.

https://visions4netjournal.com/vinta...tv-page-two-2/
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  #150  
Old 11-24-2017, 02:45 PM
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Update: we have been working on our RCA 21CTC55 receiver. Bottom line we intend to do a third test soon.

Below is what we wrote for our blog.

“We are very excited, proud and pleased with the results Mike and I achieved restoring this RCA 21CT55, a 62 year old television. Credit also to Dave, Kevin, Walter and Bob. I’m not ashamed to say “I like showing it off”.

A comparison test of a 1954/55 RCA 21CT55 and a 1958 RCA CTC-7 Worthington.

A new test to compare the image and color reproduction of the two sets. We wanted to show the differences in the first production 21 inch color set with wide-band, six IF stages and superior demodulation. The 21AXP22 also has the wide color gamut phosphors. The CTC-7 came four years later and considered to be the first truly reliable RCA color television. This CTC-7 has a rebuilt 21CYP22A. It must be said that both CRT’s tested “Good” at cut off, but the 21CYP22A tested very strong and the 21AXP22 tested weaker. The red gun in the 21AXP22 is the weakest.

We found a good quality, low loss signal splitter in my “pile of stuff” and hooked up both sets, so we can photograph both simultaneously. Experience with the camera I’m using (not the best) shows that ambient light in the room will influence the true color reproduction subject to the cameras limitations, because the camera is reading ALL the light in the room. Because collectors like to see the cabinet as well as the images, we can limit the ambient light interference by dimming the light source just enough to show the cabinet highlights with the majority of the lit screen composed in the viewfinder.

In photographing both CRT screens at the same time in the same frame, we must move further back and the ambient light will definitely influence the results. We must eliminate the light and photograph in near total darkness.

Both sets were adjusted and set up to RCA procedure recommendations. The two sets were first adjusted by eye individually for the best combination of color saturation, hue, brightness and contrast. No test instruments. (the eye can be the best test instrument). This is subjective, what I like, you may not like. My eyes have been “trained” to prefer ISF calibrated color starting in the 1990’s. I don’t claim to be an expert. ISF color calibration is scientific and quantitative and not subjective.

We used the Gentlemen Prefer Blondes DVD. It is known for great quality, three strip Technicolor.

We powered up both sets and let them settle in for 30 minutes and tuned off the lights. This time we had to take an “average” exposure. Unlike a good DSLR, my camera only has one focus and aperture point to set. We set the camera focus and exposure point in a darker area equal distance between the two lit screens. This created under exposed dark screen images, so we compensated by increasing the exposure with the camera to match what my eyes were seeing.

Both sets have fans added to the flyback cage to help cooling. The fans can be switched off. Both sets are protected by a Furman Discrete Symmetrical Power Model IT Reference 7.

After this test was completed, it occurred to me that we should have calibrated both sets using the SMPTE color bars from the Joe Kane Video Essentials DVD and blue filter. Maybe next time when we get a good DSLR.

Update notes and analysis: During the test which took over an hour, the 21CT55 screen images enlarged and increased in brightness. The CTC-7 stayed constant. The CTC-7 came up about 10 seconds later. In these shots and live, to my eyes, the 21CT55 consistently resolves more detail then the CTC-7. The geometry is adjusted better in the 21CT55. Look at slides 1 and 9. Blue shifted to violet. The CTC-7 could not register the bright spotlight scenes properly during the dance sequences. (Slide 26) The facial tones shifted to green and the dress shifted to violet. This could be adjusted, but we wanted to leave all setting the same from start to finish. The CTC-7 images are slightly brighter but is expected in the newer 21CYP22A. You can also see the differences in the red phosphors and the 21CT55 shows better details in the shadows and in bright areas. The results of this test show that we need to adjust the 21CT55 “warmer”, less blue and the CTC-7 should be “cooler” more blue.

Onward we go. Maybe my wife will buy me a nice DSLR for Christmas? Hint …..��❤️ The Tournament of Roses parade is coming soon. We intend to do a third test prior to the parade live telecast via rooftop antenna converted to analog, after calibration with the SMPTE color bars and blue filter.

Back on that historic day, January 1, 1954 when RCA and NBC broadcast the first coast to coast color program of the parade, folks in my hometown of Milwaukee could not view that color broadcast unless they were invited to one of the four private demonstrations or the one public demonstration at a television dealership. The color televisions used for those demonstrations were prototype Model 5 receivers.

The following year parade telecast on January 1, 1955, could be viewed on Admiral, Westinghouse, RCA, and other color sets, including a 1954/55 RCA 21CT55. Next years telcast (January 1, 2018) will be our first opportunity to recreate that historic event, but this time we will see the technology differences made possible with modern color cameras and studio chain equipment. Let’s do this.”

Once again, we can’t give you a direct link to the slide show. The slideshow and future slideshow can be viewed at the bottom page of this link:

https://visions4netjournal.com/vinta...tv-page-two-2/
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