Westinghouse H840CK15
 

I picked up the Westinghouse today from Dwight here in the Metro-Detroit area. My father went with me, and after going out for a late dinner, we decided we weren't going to try to carry the chassis plus 15GP22 up to my walk-up apartment.

Since I have sold off most of the items that my parents were very graciously allowing me to keep in their unused basement, we decided to take it out to their house near Flint to stay temporarily. He called my mother, explained the situation, and she begrudgingly allowed the Westy in the house. Thanks Ma! :o

We set both chassis on a table in the main room and moved the cabinet back deeper into storage.

We turned immediately to testing the 15GP22, and were pleased with some slightly encouraging signs. The heaters lit normally using my regulated 6.3 volt supply, and drew normal current. It passed a date with my tesla-coil, and I put it on the Beltron using hastily made clip leads. To our surprise, the tube shows excellent emissions on all three guns, with the red looking the strongest, and the blue looking slightly weaker than the green (and taking a tad longer to "wake up").

Neither he nor I saw any pink or purple glow between any elements in the gun like I have when testing other gassy 15GP22s.

The meter was not pegged on any gun, but we still haven't tested cutoff (the Beltron can not do this). Like the idiot I am, I left my Sencore at the museum by mistake, so I will have to wait for further testing in November when I get back from Ohio. I think the Sencore will be a bit more conclusive. If I find I can get the meter to peg on the Sencore with certain settings of cutoff, then it is clear the tube is gassy. If cutoff responds normally, then the tube is quite possibly good.)

Tonight was by no means conclusive, and I'm going to continue to assume the tube is a dud. That said, I may get a pleasant surprise when I get the tube on the Sencore, and eventually (God willing) a working 15 inch chassis.

Thank you again Dwight! :thmbsp:

I've determined how Dwight got the low readings for emissions by replicating them; he accidentally connected the G1 lead from the B&K to G2, not G1.

Some photos of the chassis and jug:

https://thumb.ibb.co/hkYXVb/20171006_223725.jpg https://thumb.ibb.co/mQxRqb/20171006_223744.jpg https://thumb.ibb.co/mAJo3w/20171006_223801.jpg https://thumb.ibb.co/bBmaiw/20171006_223808.jpg https://thumb.ibb.co/hbOcwG/20171006_234108.jpg

Any ideas on what causes that weird swirling pattern on some color CRTs? I had a 21CYP22 with the same damn thing. It didn't seem to alter the picture in use, but it looked like hell when the set was off.

Perhaps RCA continued their prewar policy of selling "lesser" CRTs to competitors and holding the best for their own sets.

The 15GP22 in this set was built in the 13th week of '54.

The getter above the blue gun looks a bit odd to me, almost like a small portion of the center has flaked away from the glass. It isn't white though, everything is still a dark grey/black color:

https://thumb.ibb.co/cg3V0b/20171007_121913.jpg https://thumb.ibb.co/e3216G/20171007_121803.jpg https://thumb.ibb.co/j8u9tw/20171007_121807.jpg

The other two getters look fine, and actually a deal bigger than the getters on the tube in the CT-100 I sold:

https://thumb.ibb.co/fpx7fb/20171007_121840.jpg https://thumb.ibb.co/hsdDLb/20171007_121849.jpg

Impressive! that chassis is a beast! Is the circuitry much different from the CT100, or did Westinghouse not get innovative?

I assume the chassis is copper, like my h22t155, or is that rust?

I have seen drying patterns in some early kasil settled phosphor tubes, but not rings like that... could that be a moire pattern perhaps generated by poor contact of the silk screen during the screening of one of the phosphor colors? Seems likely that RCA would sell less than perfect tubes to competitors.

Perhaps the getter above the blue gun was the first one flashed after "pinch off", in a fairly poor vacuum. :scratch2:

Looks like a very fun project.

jr

Totally different ball of wax compared to a CT-100. Difference demod (R-Y and B-Y), but the mixing is done CT-100 style with seperate triodes for RBG in the adder section and a triple diode clamp.

No traditional PLL like the RCA, nor the shock excited crystal approach of the 15 inch GE. Just a color hold control up front. The hue is on the rear panel like on the GE. What were they thinking?

Totally different HV and focus section compared to the RCA. Uses three 3A3s in a doubler arrangement for the ultor and a 1X2? for the focus. According to an old post on the H840CK15 from Folsom, this set has the most stable HV of all the 15 inchers.

Twin 6BG6Gs drive the flyback, compared to the 6CB5s and 6CD6s used in other sets.

The set also makes use of the unusal 6BK5 tube, a minature tube ultimately derived from the 6Y6, 6W6 family. One for audio output (about 2ish watts) and one to drive the delay line.

The audio section in particular leads me to believe this was the brainchild of a Westinghouse engineer and not some copy cat chassis; Westinghouse was one of the only manufacturers using the 6BK5 and 6BN6 combination to lower parts count. I think Zenith may have used it too.

The chassis is copper plated.

I couldn't resist the temptation to retest the tube today with the Beltron. Dave Pike will be coming over with his Sencore CR-70 to check for cutoff later this week.

Red:
https://thumb.ibb.co/kL5a1G/20171008_132638.jpg

Blue:
https://thumb.ibb.co/csNcFb/20171008_132911.jpg

Green:
https://thumb.ibb.co/cwJjvb/20171008_134316.jpg

I've never seen a tube this closely matched on all three guns, so I'm inclined to think it's gassy, but I got no indication of gas while testing it (blue or purple glow between the cathode and first grid) or with the tesla coil... :saywhat:

I need to find someone in the area with a working 15 inch chassis.

Very curious Ben. :dunno:

Meter readings seem suspicious just like a gassy 15G I have. But the fact that you cant get any neck glow, even with your Tesla coil makes me believe the tube is NOT gassy. I have never seen a gassy tube that failed to give a purple glow with a Tesla coil.

Your getters look just like the ones in my aforementioned 15G (shiny and black) which is gassy, but my tube glows like a neon sign with my Tesla coil.

CR70 cutoff test should prove it one way or the other.

Must be a manufacturing defect, right? I don't see how it could happen afterwards. I thought the imperfect CRTs ended up in test jigs, but was there ever a 15-inch test jig? I'm guessing not.

Good luck, I really hope your picture tube is functional.

What tesla coil do you use? Any tesla coil of sufficient power should show gas... now I'm going to check and make sure it's working properly with an unused CFL...

The fact that you have seen the same sort of swirl on two different tube types that used different methods of application is really interesting. I have never seen anything like this.

In the 70's, Sylvania came up with a brighter phosphor slurry that was thicker than usual. Motorola had trouble using the thicker slurry because of broad swirl marks, but they were faint and only showed up when the tube was lit. Engineering staff were commandeered to take two identical 19 inch sets (except for old and new slurry) home and get unprompted comments from their families to find out if anyone could see the swirls as well as the difference in brightness.

Can you hold up something with a contrasty pattern to the tube and see if the reflection is distorted? Wondering if the swirl is a defect in the glass phosphor plate.

Wayne,

I held a sheet of log paper up to the tube. It was sort of hard to see, given that there was a second reflection from the front of the jug itself, but no, the reflection of the pattern from the inner glass phosphor dot plate was not distorted.

The swirling is definitely the phosphor itself.

About Tesla coils and CRTs. I have a Tesla coil or three. I used them to start discharges
with microwave generators to make Fluorine or Oxygen atoms for my research.
They are exactly like the pictures I see offering the CRT tester ones in ebay.

But ... is using one to test a 15GP22 in a CT-100 (in the set) dangerous to the
parts of the set, like the yoke or purity magnet? I would of course disconnect everything.
The CRT itself is immaterial ... its red gun is truly dead.

For testing the CRT for gas with a Tesla coil, I removed the purity coil assembly and yoke. On the Westinghouse chassis this is extremely fast. Loosen four nuts, slide everything back and you're done.

I removed them simply because it is easier to see discharge with more of the neck exposed.

I would keep the Tesla coil away from the base as much as possible; check up by the convergence and focusing electrodes. A Tesla coil of sufficient power can burn out a small incandescent light bulb; I imagine a tube heater would be fundamentally no different.

If your tube is gassy, it will be very apparent with the Tesla coil.

Another good test for gas is a Sencore CR-70. Play with bias setting. At sufficiently low bias voltage the meter should peg; the cutoff control fails to control the beam current like normal if the tube is gassy.

Actually, with a sufficiently gassy tube, the voltages from the Sencore are sufficient to strike the gas and cause discharge between the cathode and grids one and two.

See this post for an admittedly poor picture of what I'm talking about:

http://mail.videokarma.org/showpost....0&postcount=16

I would be very curious to know if you can see the faint purple pink glow between the red cathode and first or second grid in your tube Doug.

Gents, is ths what we are talking about here?

https://www.amazon.com/Oudin-Coil-Te...rds=tesla+coil

Tis like the one I remember seeing at various CRT production/rebuildng facilities years ago.

not affiliated,
jr

I have two, one similar to that and a smaller one that operates from a 9 volt battery. Both can fully illuminate a CFL, neither shows any gas on the CRT.

Hopefully this isnt too off topic, but it has been intriguing me for awhile now. Is there a reason why the H840 uses RY GY demodulation and the CT-100 uses Q demodulation? Both sets are from the same year and I believe RY GY became standard soon after. Did RCA consider Q demod superior to RY GY?

I/Q demodulation is superior to difference demodulation, yes. (For the record, the Westinghouse is R-Y and B-Y, and it was this that briefly became the preferred demod axes). X and Z demodulation, as explained in Wayne Bretl's response to my query on difference demod in another thread, is essentially just a variant of R-Y B-Y demodulation.

I/Q is more expensive to implement. With R-Y B-Y, you have red and blue essentially ready to go right from the demodators. Just amplify it to drive the grids of the CRT and mix the luma in at the cathodes of the CRT. G-Y can be recovered from a simple network of passive components mixing R-Y and B-Y in the correct proportions. Then amplify it, send it to the grids, and ta-da, you have a color picture.

Note however, that this is not how the Westinghouse accomplished this. The Westy uses triodes to mix the difference signals and the luma, amplifies it, sends the result to a DC clamp, and then the grids are driven with actual R, G, and B.

The RCA method is more complicated. I and Q (or -I and -Q) are recovered from the demodulators. I and Q are then inverted. You now have I, -I, Q, and -Q available. These four signals are mixed in the correct proportions, along with the luma, so as to produce R , G, and B. These signals are then sent to a DC clamp, and the grids are driven with true R, G, and B.

More complicated = more costly. It isn't hard to see why RCA abandon this method of demod for the CTC-4 and all subsequent chassis (during the tube era at least). Difference demod is cheaper. If you want to sell more TV sets, you find a way to make them less expensive.

Now, would the difference between these demod methods actually have been visible on a Westy and a CT-100 both connected to an antenna circa 1954: not no, but hell no.

Watching a 15G is similar to watching TV through a screen door: the dot pattern is plainly visible and all fine detail is essentially obliterated.

On a 21 or 19 inch set, I think the difference may have been visible to very observant viewers under the right set of conditions. Whether those conditions would have existed "in the wild" with an antenna on the roof circa 1954 is again doubtful.

Interesting, seems like Q demodulation was just another factor in the poor sales of the CT100.

As I probably explained in another thread, the transmitter side Q filters were really not properly specified by the NTSC/FCC. To guarantee good results, Q baseband should have a notch at 900 kHz, so that in the receiver, when the upper sideband is killed by the receiver 4.5 MHz sound trap, the lower Q sideband also has no energy at 900 kHz below chroma and there would be no quadrature distortion, which was the aim of I/Q modulation in the first place. So, when I/Q demodulation was tried on some later sets with larger screens, the quadrature distortion could be quite visible, and results depended on the Q response of the particular color encoder in use at the studio. So, I/Q was a great idea, but suffered from under-specified filter standards. I believe none of the experiments that led to the choice of I/Q actually used an end-to-end system including the RF/IF parts. Later, when the whole system was being tested, there were a million problems to fix, and if the quadrature distortion was visible (say on a large-screen trinescope), it would have been easy to ignore as possibly a small receiver issue that could be fixed later.

Edit: Also, probably posted by me elsewhere, I did an extensive series of tests on I/Q demodulation when I worked for Zenith in the 80s, and even using baseband I/Q with no quadrature distortion, there were some effects that people weren't used to, like the vertical strokes of yellow movie titles turning orangish because the I signal was full amplitude for narrow objects while the Q signal was smeared and reduced in amplitude.

The last three comments are way over my head.

From a common man’s point of view (average but devoted), it seems to me from recollections and observations back in 1956 and subsequent up to approximately the late 70’s, the “state of the art” in television color broadcasting was incapable of exploiting the potential of the 50’s CRT color reproduction and resolution capabilities.

The 15G actually has pretty poor resolution, owing to its diminutive size. Good color yes, but the 19 and 21” sets are where you could really start to get a good color picture at a size you didn’t have to squint at.

Brought the set up on a Variac today. I figured if I could get the set to produce HV that would definitively say whether the 15G is gassy or not. No HV, and before I had a chance to poke around further a small electrolytic under the main chassis popped.

If I'm not mistaken X Y color demodulation required limiting the bandwidth of the wider band signal in the transmitted I/Q signal. On something like fireworks where there are colored lights of diminishing size the difference between wide and narrow band color might be noticeable in a side by side comparison. Were there viewers that smart, signals that good, two such sets side by side....Perhaps at the FCC hearings prior to NTSC approval and in some TV labs, but unlikely in the real world.

Congrats on the set Ben.

Thanks Tom! :-)

After much thought and deliberation, I've decided the Westinghouse restoration is more than I want to tackle, and admittedly a bit more than I feel I am capable of.

So, Nick Williams will be restoring and aligning the chassis, a fine furniture restoration shop will be completely refinishing the cabinet, my friend Kevin Stankovic will be drawing up model of the mask and knobs in CAD and then reproducing them, and I will simply cooridnate all those efforts and do the final assembly and setup myself.

I welcome the challenge.

I have a Halolite on the bench right now, that will be followed by another 621 and a pair of Curtis Mathis color chassis, then I’ll be ready for the westy.

The big problem with I-Q demod is that to get it really right required two
delay lines, one for Y, one for I. And to get them right and the filters with good phase response is not easy ... without digital (or bucket brigades).

My personal opinion is that best is to use any two axes and get the response
quite flat to about 700-800 kHz then rolling off to zero at 1.5 MHz. on both
axes. Few folks notice the resulting bleedthrough from I into Q. Using
equal bandwidths the results are identical independent of the axes used.

However, other people may seriously object to the bleedthrough.

Yep. It was less disconcerting to have the color saturation of details reduced than to have the wrong hue - and if the level of quadrature distortion was low enough, at normal viewing distance in the home it appeared to add some color detail without being obviously wrong. With the engineer's nose to picture tube, the quadrature was visible as a rainbow effect on small strongly colored objects, but it also tended to be hidden by the luminance overshoot due to video peaking.

Since later solid state sets usually simplified the chroma bandpass such that they had this gradual chroma cutoff rather than the classic double-tuned response, it meant that they could actually benefit from composite video input that had double sideband chroma, meaning that the color detail would be somewhat better with a digital source (DVD or digital broadcast converter) fed into the baseband composite input than was possible with RF feed.

Demodulation had nothing to do with poor sales.
The Consumer Price Index says $1,000 (price of CT-100) in March, 1954 is supposedly equivalent to $9,127 today.

This raises an interesting question. What exactly is "wide bandwidth" chroma demod? Where does one draw the line in the sand and say this set is narrow band whereas this other set is wide band? I guess it is more accurate to say that some sets are wider or narrower relative to one another...

Take for instance the CTC-2 vs the CTC-5N. Both are "wideband" but the CTC-2 demodulates along I/Q and has extended I response. The CTC-N uses difference demod and starts rolling off at about 600 kHz on both axes, yet both are described as having wide chroma bandwidth on Ed's site. The CTC-2 has wider bandwidth, than the 5, but compared to the CTC-4 they both would qualify as "wide".

The actual terms are next to meaningless, but I recall someone telling me it’s actually more correct in most cases to call narrowband circuits ‘equiband’ since most difference circuits have about the same frequency response in both axis. Maybe it was wayne?

I built a small Tesla coil yesterday using the self-tuning, and extremely efficient, "Slayer" exciter with junk box parts. This morning, I tested it with a 150 watt replacement CFL bulb. Lit up like a Christmas tree.

Retested the neck and face of the 15GP22 for gas with the new Tesla coil. Nadda.

If Dave and I get normal looking cutoff tonight, I'm calling the tube good.

The ability of the RF from the Tesla coil to excite the gasses in a sealed low pressure tube is inversely proportional the pressure of the gasses inside the tube, over a fairly wide range of pressures. At about 3 torr, the pressure inside of the typical CFL, the Tesla coil was capable of exciting the gasses. Pressures too high will not allow the excitation of the gasses to be visible. On the opposite end of things, a pressure too low won't allow one to observe excitation of the gas from a Tesla coil either.

Once we get below about 10^-3 torr, the excitation of the gasses from the Tesla coil should no longer be visible. A CRT with a pressure above about 10^-4 torr is useless and will start arcing. A tube at 10^-6 to 10^-9 is ideal.

Given what I've observed thus far, I can safely conclude that the tube must be at a pressure no greater than 10^-3 torr. Even a Tesla coil isn't as fool proof as I had thought... Nick is right, the only good test is a working chassis.

Yes, the major difference is non-equiband (I/Q) vs. equiband; a secondary difference is how wide the equiband demods are. Generally, if the demods are "high level" (have high gain and are coupled to the CRT without further amplification) they will have more roll-off due to stray capacitance than a "low level" demod that is followed by an additional stage of amplification (like the RCA X/Z system). The X/Z system was truly a well-optimized trade-off of cost and performance, which was not improved on for many years.

Question for the 15 inch gurus: does pin 13 of the CRT itself typically show signs of having had 10 kV or so on it? Or would you only expect to see marks on hole 13 of the socket?

The CRT has absolutely no signs of having had convergence voltage on pin 13. I mean none. But the corresponding hole in the socket is pretty chewed up...

Maybe the tube was replaced at some point.

The CRT is good:

• The heaters lit normally, and drew normal current
• The neck didn't get any warmer than a typical color CRT neck
• Neither Dave nor I saw ANY glow whatsoever
• There is no discoloration of the cathodes or grids
• Multiple passes with three different tesla coils revealed no gas
• Cutoff on all three guns responded normally, though the pot needed to be in a different position for each gun
• And finally, the Sencore showed emissions results very similar to the Beltron

:banana: :banana: :banana:

Dave was fairly confident when he left that the tube would produce a good picture; so am I.

Now to get the chassis to Nick...

Now that the CRT is know to be good are you going to pony up some more cash, or was it an all sales final kind of deal :deal::D

Congrats Ben! I would bet your assumption that the tube had been replaced at some point, is correct. The tube seems to test like NOS. And the fact that you found some carbonizing only on the socket at pin13, I think your assumption that this is a replacement crt is probably correct.

In addition, it is my belief that late production crt's from RCA were more likely to be free from leak defects as RCA got better at producing good leak free tubes.

When you get a chance to pull the tube, it will be interesting to see if it has been re-necked which would indicate a tube that was either rebuilt at RCA or failed QC and reworked during original production. I have seen a couple 15Gs that were obviously renecked/rebuilt/reworked by RCA. Although this is just conjecture, I think that after the original production run was over, RCA rebuilt duds to have a supply of 15Gs for RCA's replacement crt division. It is well known that replacement crt price lists showed the 15G to be available for quite a number of years.

Dwight and I have been in contact, and he's happy the tube is operational. The trade was pretty damn fair considering the missing parts on the Westy. If he wants to reveal the details, that's his prerogative. The deal is done.