HOT Current vs Fuse Current #2
 

I am now using a 22mf electro across the analog VOM for HOT current measurements. I corrected the posting where I measured 128ma using a DVM. It now reads 180ma at both Hot cathode and at the HV fuse. Seems reasonable since current in is current out in these simple circuits. Ultor / HV reg current only amounts to a 1 or 2ma difference if you want to be nit picking.

Glad to hear I was right.

glad to hear that tom got his set performing properly.thats what we are glad about

My pet peeve is misinformation, sorry if that anoys some of you.

i am sure the "misinformation"wasnt purposely intended to peeve you.i find tom s posts very informative,well written and enlightening.no competition here in this forum.some of us are still learning,others teach and then there is the one who knows everything.i am still learning and glad to associate with these fine fellows.
i personally dont have a pet peeve.just realize everybody has different looks,tastes,actions,etc.can you imagine a forum where everybody was the same?how would you like to talk with people just like you?it would get boring very quickly.as a matter of fact,i am bored with this post.goodnight

FBX Setup is OK
 

I just made a major capital equipment purchase, a Heathkit HV Probe for $39 including shipping. When used with my 1950 Heathkit VTVM I was finally able to setup my 6BK4 HV reg after I cleaned the 66m resistor with lacquer thinner. It was reading 24m with 50 years of crud on its body. Now the ultor is held at the desired 27KV constant at all brightness levels. Some important readings:
At ac in of 115vac, B++ is 424v, horz system current at fuse is only 172ma (same as HOT cathode), boost is 725v, focus is 5.5kv, Ultor is 27KV. After > 2 hours operation, the FBX primary and HV doughnut were barely "body temp", < 110F!
The last major effort will be the horz dynamic convergence system. The latest pics are with only vert convergence:

Glad 4 ur success
 

GLAD 4 UR SUCCESS:banana::banana::banana:

Those screen shots look pretty good to me.

Dummy question here: What's the reason that HOT circuits typically don't incorporate some type of current regulation circuitry? The way I understand it, is that if you loose Horizontal drive, you end up with a melt down.

Kevin

My attempt at a dummy answer--

Seems to me that the tuning of the HOT / flyback is already delicate enough under good circumstances. Adding another circuit or two for protection in the case of complete horizontal drive failure might have made the whole thing even more unreliable.

How often were there cases of complete horizontal drive failure?

Easy enough to do in the IC age (and they were probably more concerned with keeping HV/x-rays under control than protecting any circuitry)

Maybe I should have stated current limiting instead of regulation. Probably wasn't a threat back in the day when OEM parts were available. But I've heard horror stories of very early paper coupling capacitor failures on mid 50's sets.

Kevin

The simple answer is that anything more sophisticated than a fuse would have been way too expensive with tube technology - the simplest current comparison circuit would require at least one more tube stage. Safety shut downs became affordable with the use of transistors, and eminently affordable with ICs. Even then, there were cases of tolerance issues causing unnecessary shutdowns sometimes. With the wide tolerances on consumer tube circuits, this would have reached intolerable false failure rates.

I suppose if the HOT was self-biased, then it would not provide a large enough current spike as required. Are those running something like a class C TX output?

Kevin

The HOT under normal operation is either on hard, so the voltage across it is low when current is flowing; or it is completely off, so the current is zero while the voltage is high. Therefore , the power dissipated is low, because the product of (voltage x current) is low or zero. Without the drive waveform, it can be somewhere in between - this condition of having both current and voltage means that the power dissipated in the HOT goes up drastically.

So, another way to describe the HOT ckt would be like a "switching power supply", I reckon, and class "C" is not too far off.

As we know, in an SMPS, the switch transistors must be on or off, and nOT much in between..or WAY too much current--and then destruction--immediately follows.

:thmbsp:

oh yea. ive had my fun building DIY SMPS circuits. WEEEEEEE

especially when your not pushing the gates hard enough, you power up your circuit, works for a little bit then... KERRRPLOWWWWWW

weee yea what fun....

Of course a flyback is a type of switching power supply (having designed a couple).

And sweep tubes were commonly used in lower cost amateur SW transmitters, probably running pretty close to Class C (I think you could get 100W PEP SSB out of a 6JE6). You tuned the final to minimum current.

I don't see a problem with installing a bypassed cathode resisitor to limit plate current, in the event of drive signal loss. My mid 50's RCA B&W has this. But a lot of TV's don't have it. Were they too cheap to spring for a resistor and cap? What am I missing?

Kevin

Perhaps the added cost was not justified? I read that one resistor was saved in the matrix of the 21CT55, vs the CT-100. You might be surprised the lengths OEMs go to for cost reduction; some of it borders on a safety risk, especially with cars.

The resistor elimination in the 21CT55 matrix from the CT100 design was a patent dodge. RCA did not want to pay royalties on I/Q demodulation. Well, thats the story I heard. RCA was known to do almost anything to avoid paying royalties.

John. I came to the same conclusion recently. The quadrature transformers for the CTC2 and CTC2B chassis have different part numbers. They would have to be since the demodulation angle is different for R-Y demodulation than it is for I demodulation,

I do not have a CTC2B chassis to test my theory, but one must rule
out the possibility that the CTC2B chassis does not properly decode the color signal transmitted by an NTSC broadcast transmitter. The two color signals, I and Q, that are trasnmitted by NTSC standards are in quadrature. In the CTC2B the decoded chroma, Q and R-Y, are not. When a quadrature signal is encoded, it must be deconded in quadrature if crosstalk is to be minimized.

If I am right, the CTC2B chassis is inferior to the CTC2 chassis when decoding an NTSC broadcast.

Now, it is always possible that some stone has been left unturned by me. Perhaps eliminating the one insignificant-in-cost resistor in the CTC2B matrix somehow negates the not-in-quadrature problem. I don't know.

BTW: I believe it was probably Philco that RCA was dodging.

Pete

Comparisons before and after FBX replacement.
 

Here are preliminary comparisons of the original FBX vs the replacement FBX installed in my 21CT55. The screen is still too wide, must be the original yoke is more sensitive then the newer yokes intended to be driven by the replacement FBX. No, I wont try to find a newer yoke………..Tom

When I had to come up with a flyback for my CBS field sequential color adapter (the original was missing) I had to experiment with various things to get the replacement to work with the yoke. I also had too much width. I added an inductor paralleled by a resistor in series with the yoke. Maybe something similar would work for you:

http://www.earlytelevision.org/cbs_c...storation.html

Hobble-up Width Control
 

Steve, thanks for your interest in my 21CT55 reactivation. The new FBX is very efficient, delivering 32kv maximum ultor and 800v boost with B++ of 398v. Fuse current is same as HOT cathode and runs at only 174ma. B++ is limited with power resistors in the power xformer hv secondary so I can select three B++ voltages with 115vac input from my Variac: Low is 374v @ 160ma HOT, Med is 395v @ 170ma HOT, High is 420v @ 182ma HOT. After running for 3 hours at Med, FBX is bearly warm at B++ of 395v. Excessive screen width is the only major problem. All RCA's CTC7 and above have no width control. They must rely on tight spec'd parts in the Horz/EHV system to give just the right over-scan.
Your experience with using inductors to load the FBX and bleed-off drive to the yoke is consistent with my Fink '57 TV engineering handbook descriptions of width controls . Most of them were shunt where yours is series dropping. I intend to try various schemes to pull mine in.
The preliminary pics I posted above were somewhat disappointing to me. I definitely have chroma leakage in the Q channel since I don't have the proper output filter values installed. Also my camera was on AUTO and bad focus. Here's some full manual pics. The first pic is a stitch of extreme crop of new vs Sony Pro. Q chroma leakage is obvious:

My 7 and 9 both have a plug on the yoke you can move around to get the desired width, while my 4 has an actual switch.

my 9 has that plug also.these sets produce some of the most pleasing colors.i have it along side of my zenith space command and the 9 s flesh tones are remarkable.my xl100 and the zenith chromacolor with the 25vdmp22 are better,but not that much.love those old rcas!

What are the other 4 pics? Chroma dots on every other one? - like with and without 3.58 trap in the luma.

By the way this is what the horizontal linearity or efficiency coil is for; to tune
the HOT circuit for minimum current which, at least in my B&W sets is also the best linearity. I imagine it's the same in color sets too?
Cliff

RCA was the last major mfr. to use intercarrier audio. I guess Sarnoff didn't want to lower himself to paying royalties to Motorola Inc.

Frankenstien Lives!
 

Here are some later screen pics of the Ferris Day Off. The stitches are before and after FBX swap. Some are after vs Sony. With the exception of too much width, picture quality re facial color graduation and non-combfiltered fine detail, typical of my 21CT55 aka Frankenstein, has been restored. Following advice of this thread, I purchased at great expense DVD of Wizard of Oz and Blu-ray of Gone with the Wind ($10 and $12 respectively. I am now ready for the Lollipop Color of the original Technicolor. I hope I'm not disappointed………………Tom,

Looking real good Tom! :banana: Look forward to lolipop color screen shots on the old gem. 1938 "Robin Hood" is another good one for Technicolor, and I use it often with the 4.
Kevin

It's alive, Its alive! Tom you should change the title of this thread. Your 21-CT-55 is most certainly resuscitated.

-Steve D.

Please pardon my language but that thing looks goddamn awesome! You really should change the name of the thread! That chick sitting on the bricks drinkin' coffee looks hot! (that's my type:D) The detail on the CTC 2B has much better detail too! It puts the Sony to shame!! Oh yeah, did I mention that chick's hot:smsex:

21CT55 is Alive and Well
 

My "Frankenstein" 21CT55 is now off life support and performs as good as original. The screen width is still too wide and has some video foldover that has to be tracked down and fixed. Also the chroma section is showing some color drift near the bottom of the screen occasionally. With 115vac mains, I am running B++ at 396v, boost at 790v, ultor at 27kv. Horiz system current measures 170ma at the fuse, therefore the HOT cathode is the same or less. Please lets not rehash this issue, OK!
I've been playing the "Wizard of Oz" DVD. Am very impressed with the near saturated (Lolly-Pop) screen colors. The screen looks much better than my digital cameras can capture. Seems the CTC2B video system and the 21FBP22A crt have greater brightness dynamic range then the camera's. If I run the camera's brightness down to get good pure whites (tablecloth, blouses etc) without blooming, I loose all low level dark detail in the shadows. The CRT has no problems with these scenes. I find this very disturbing and wish some VK members would drop by for direct viewing.
Anyway, this ".....death" thread is no longer relevant and I intend to go back to my original "RCA 21CT55 #8802897 is Alive!" thread. I feel good about this...........Tom

The limited dynamic range is something that plagues most digital cameras. I have done several exposures of the same scene, overexposing for shadow detail in one, underexposing for highlights in the other, and so on, and piecing the results together in photoshop. This happens a lot when trying to scan in old slides as well, particularly Kodachrome.

Digital Camera Dynamic Range
 

My camera is an old 4mpix Canon S40, Judy's is a newer 7mpix Olympus SP-550UZ. They both have dynamic range considerably less than the 21CT55/21FBP22A screen display. I wouldn't want to resort to the heroics of Photo-shop enhancement to demonstrate this ancient CTV. Maybe it's a insurmountable problem. I shoot with ISO of 200 and 1/30 sec. usually F5.6.
The resolution is set for 1024 X 768 native so I don't have to scale it down for posting. Morie is not a big problem. Any suggestions..............Tom

Part of the problem is that cameras (digital or film) that produce pleasing pictures of natural scenes have a contrast boost in the mid tones, with a gradual S-curve compression of highlights and lowlights,compared to the original scene. TV systems have this contrast boost as well. The result when photographing the screen is a double contrast boost. The raw capture of a digital camera actually has enough dynamic range, so if you can capture in raw mode and reduce the contrast in Photoshop, you may get decent results.

There is one other problem that can occur (less so on color CRTs than monochrome) - if the CRT is resolving scanning lines with dark spaces in between, this means that the average level in an area (which the eye can see quite well) is made up of bright lines and dark spaces. Both film and digital cameras have a hard time accomodating that dynamic range. The actual video variation of the bright lines ends up compressed into the highlight region of the digital sensor or film when the average is correct. For best gray scale, the focus (either CRT or camera) needs to be just not so sharp that lines with spaces are visible. Some film recording systems used a vertical spot wobble at a high frequency to just make the bright lines touch each other. Your use of reduced resolution may help by averaging nearby pixels, but it may not be a cure if some of those pixels are overexposed and some are seeing black. An alternative is to underexpose the average, then blur the lines together precisely in Photoshop (by reducing resolution), and then boost the average back to normal. This problem is similar to taking pictures of stars at night. The system really can't handle the dynamic range, but a tiny bit of defocussing changes the brightness modulation somewhat into an area modulation (brighter stars light up bigger blobs of pixels) and gives the right final impression.

So, something to try:
Shoot at highest resolution, with exposure compensated down by at least one stop;
Then reduce the resolution to average the bright and dark adjacent pixels;
Finally, increase the levels to the correct average.

Tom,

This is absolutely astounding!!! It goes to show that there are people here on VK that have a level of technical expertise that goes above and beyone anything that many of us "re-cap and refinish" restorers like myself, could possibly ever approach.

You have accomplished something that only very few on this forum could have even attempted.

Congratulations, you have my sincere admiration and respect for what you have accomplished!

Thanks for Your Replies
 

My screen shots are good, but when I view the actual screens of the 21CT55 and my comb-filtered Sonys I realize my two cameras don't do them justice. Leadike and Wayne have offered possible solutions to increase brightness dynamic range of the shots, Since I don't have Photoshop I've decided to try Wayne's suggestion of processing RAW format on both cameras. This seems daunting but worth the effort. As for Bob's reply, I am most humble. I consider him the primer restorer, both in cabinetry, electronics and CRT rebuild technology. All his projects are museum pieces, including his recent 21CT55, which gives me brief pangs of guilt for what I did to mine in '64. I'll attempt to make it up with some outstanding, RAW based screen shots from my " vertical chassis table model" 21CT55 conversion....Tom