Another Westinghouse H840CK15

[ohohyodafarted]

Here are the DC resistances of the vertical convergence transformer. These readingx are taken directly from a known good trans that I removed from my CT100 and replaced with one of the replacement transformers that Folsom had for sale back in the day. The original has been sitting on my shelf for about 10 years because I am saving it in case of a failure in one of my 15" color sets.

The resistance of the primary is 1060 ohms.

The secondary is 20,300 ohms center tap to one end.
and 8700 ohms center tap to the other end
with an overall end to end resistance of 29,000 ohms.

That equates to about 27,645 feet (5.23 miles) of #40 wire on the secondary at 1049 ohms per 1000 feet of wire.

Hope this helps in your winding effort in the event you are unable to obtain a replacement.

Good Luck!

[trinescope]

Originally Posted by ohohyodafarted

Here are the DC resistances of the vertical convergence transformer. These readingx are taken directly from a known good trans that I removed from my CT100 and replaced with one of the replacement transformers that Folsom had for sale back in the day. The original has been sitting on my shelf for about 10 years because I am saving it in case of a failure in one of my 15" color sets.

The resistance of the primary is 1060 ohms.

The secondary is 20,300 ohms center tap to one end.
and 8700 ohms center tap to the other end
with an overall end to end resistance of 29,000 ohms.

That equates to about 27,645 feet (5.23 miles) of #40 wire on the secondary at 1049 ohms per 1000 feet of wire.

Hope this helps in your winding effort in the event you are unable to obtain a replacement.

Good Luck!

Thanks much for the information. I guess the Westinghouse and RCA transformers, although functionally equivalent, are actually constructed differently. Looking at the ad on the ETF website for the reproduction transformers, it says that 41 and 43AWG wires are used in the windings. My transformer had only 41AWG wire in both primary and secondary. The scan of the Sams folder for the Westinghouse shows secondary resistance readings of 3800 and 9200 ohms (although the scan is fuzzy in that area, so that's a best guess) whereas the RCA part as you measured is 8700 and 20300 ohms, respectively. The primary resistances are just about equal, however. My educated guess is the RCA part uses 43AWG wire on the secondary. 41AWG wire is about 1320 ohms/Kft and 43AWG is about 2140 ohms/Kft, quite a bit of difference. Using best guess turns per foot based on the location of the windings the primary is 2000 turns of 41AWG, and the secondary is 8700 + 17000 turns of 43AWG. For the Westinghouse part I get 2000 turns of 41AWG and 5750 + 12500 turns of 41AWG. Using the same insulation thickness the overall winding dimensions are roughly equal and just about fit in the E laminations.

The overall primary/secondary ratio looks to be different between these two if my assumptions and calculations are correct, but the tapped secondary ratios are nearly the same.

I don't know if I want to attempt this on my own or see if maybe Edcor or some other transformer company could produce this.

[ohohyodafarted]

Originally Posted by trinescope

Thanks much for the information. I guess the Westinghouse and RCA transformers, although functionally equivalent, are actually constructed differently. Looking at the ad on the ETF website for the reproduction transformers, it says that 41 and 43AWG wires are used in the windings. My transformer had only 41AWG wire in both primary and secondary. The scan of the Sams folder for the Westinghouse shows secondary resistance readings of 3800 and 9200 ohms (although the scan is fuzzy in that area, so that's a best guess) whereas the RCA part as you measured is 8700 and 20300 ohms, respectively. The primary resistances are just about equal, however. My educated guess is the RCA part uses 43AWG wire on the secondary. 41AWG wire is about 1320 ohms/Kft and 43AWG is about 2140 ohms/Kft, quite a bit of difference. Using best guess turns per foot based on the location of the windings the primary is 2000 turns of 41AWG, and the secondary is 8700 + 17000 turns of 43AWG. For the Westinghouse part I get 2000 turns of 41AWG and 5750 + 12500 turns of 41AWG. Using the same insulation thickness the overall winding dimensions are roughly equal and just about fit in the E laminations.

The overall primary/secondary ratio looks to be different between these two if my assumptions and calculations are correct, but the tapped secondary ratios are nearly the same.

I don't know if I want to attempt this on my own or see if maybe Edcor or some other transformer company could produce this.

Forget about the resistance numbers on the Westy schematic. They are wrong. The correct numbers are on the CT100 Sams schematic. I have no first hand knowledge of the correct wire gauges, but I would go with the numbers on the ETF ad for Folsoms trans. What do you come up with when you measure the actual wire from your trans?

[trinescope]

Yeah, I know the Westinghouse schematic numbers are wrong (1350 ohms for the secondary IIRC). Since the CT-100 part looks like it works in this set as well I'll go with the numbers I get based off of your information. I did measure a 1 foot piece of wire and got 1.3 ohms which corresponds with the 1320 or so ohms per 1000 feet of 41AWG. 43AWG should have been more like 2.1 ohms per foot. That's why I believe the parts were made differently.

My secondaries were open so I didn't have the benefit of getting a resistance reading off of the original part.

[trinescope]

I was finally able to do the IF alignment after dealing with stuck and chipped cores and two transformers with broken wires. I think I got a pretty passable response after a lot of iteration. Hopefully the color will look and sync better now. I will need to order more capacitors so I can replace the remaining paper wax capacitors still being used. Also I will need to check out the horizontal oscillator since it starts becoming flaky after being on for a while, shifting frequency a bit then back again. I need to build a 3.58MHz crystal oscillator for aligning the demodulator section. That way I should be able to set up the 90 degree phase shift using a dual trace scope and be sure it's correct before installing the CRT to the chassis. That is the pain in the rear about this set... the CRT has to be removed from the chassis to do much of anything with it beyond normal adjustments.

[trinescope]

Looks like I'm on my own as far as the convergence transformer goes, so I ordered one of those Chinese automatic coil winders and some 41AWG wire. This should make it easier to get a nice, tight, even wind and if the transformer ends up not working for some reason I can try again fairly easily. I'll first try winding the primary and see how close to 1000 ohms I get for winding resistance. That's a few days off right now. I also need to order more .1uF capacitors, and I will also get a 3.58MHz crystal oscillator for chroma demodulator alignment. My work area is in the garage, and with this 100 degree weather I'm not really doing much now.