RCA KCS100D Chassis VOT Issue

[Chris K]

Hi all. Have a cool little RCA 8" Model PT-710 with an open vertical output transformer. Tried to find the break but couldn't. There are a couple of chassis for this set and I have model KCS100D that has a VOT with a 32-1 ratio and a 22k Primary. The "B" chassis' VOT has a 35.8-1 ratio with a 27k Primary. There was a Thordarson 26S12 replacement on eBay for the B model and I thought I'd grab it and see if I could get it to work but no go. A direct replacement I believe is a Stancor VO-107. Can't find one on the bay or in the ETF parts lists. There is a Thordarson S2620 that is a 32-1 ratio but I can't find the specs on the primary resistance (can't find that one for sale anywhere either!). I guess what I'm asking for is any ideas on the full specs for the S2620 and would it work? The RCA part number for the correct VOT I need is 103266. I guess I could get a donor set because these small TVs can be shipped easily but I'm sure there are options I don't know about. Anyway, I'd love to get this cool little TV working again. Thanks for listening!!!

[Electronic M]

I think there were a different Vert output tube and circuit between the 2 versions of the chassis...If you are trying to use a vertical output transformer for the other version, then you need to change the tube and circuit wiring to match what the transformer was made to work with.

[Chris K]

Originally Posted by Electronic M

I think there were a different Vert output tube and circuit between the 2 versions of the chassis...If you are trying to use a vertical output transformer for the other version, then you need to change the tube and circuit wiring to match what the transformer was made to work with.

That's right Tom...my chassis uses the 6CM7 and the VOT I bought is for the 6CG7 in the B chassis. Not only is the tube pin wiring different but the vertical linearity pot is wired differently and a bunch of resistor values are changed. I guess it was foolish to use the B chassis transformer but...I'm learning! I suppose I'll have to either get a donor or wait until an appropriate replacement becomes available. Are there any considerations other ratio and primary resistance I need to be concerned with when looking for a replacement?

[Tim]

The resistance will not matter, it is the turns ratio that matters. Sams lists the resistance to help in troubleshooting, not as a required spec. Stancor made a universal VO transformer supposedly good for 5:1 to 50:1 if you can find one of those VO-109. Do you mean Thordarson 26S20? You wrote S2620.

[Chris K]

Originally Posted by Tim

The resistance will not matter, it is the turns ratio that matters. Sams lists the resistance to help in troubleshooting, not as a required spec. Stancor made a universal VO transformer supposedly good for 5:1 to 50:1 if you can find one of those VO-109. Do you mean Thordarson 26S20? You wrote S2620.

Yes transposition error! I believe the ETF lists a Stancor VO-109 as being in stock. I'll check.

[Chris K]

Nope...it's a VO-110 and a VO-117

[Electronic M]

Originally Posted by Chris K

That's right Tom...my chassis uses the 6CM7 and the VOT I bought is for the 6CG7 in the B chassis. Not only is the tube pin wiring different but the vertical linearity pot is wired differently and a bunch of resistor values are changed. I guess it was foolish to use the B chassis transformer but...I'm learning! I suppose I'll have to either get a donor or wait until an appropriate replacement becomes available. Are there any considerations other ratio and primary resistance I need to be concerned with when looking for a replacement?

Why not use that new transformer for the other chassis version and just change the tube and resistors to match it?....I mean yeah these sets are a bit cramped to work on, but having done one myself in one day back on Thanksgiving (away from home no less), I can say that these aren't so bad to work on that I wouldn't rewire the whole vertical circuit to make the transformer work if I were in your shoes.

[jr_tech]

Vertical circuits, RCA 8PT70xx:
Quite a few differences. Note even the HV is different
jr

[TV-collector]

Hi Chris,
A vertical output stage is like/about an audio output stage constructed.
(higher voltage/low current at the primary, lower voltage/high current
at the secondary)
As others said, there is not a big difference among output transformers.
You have here now no additional tabs.
I should try to use a transformer from a parts set with the same angle
in the vertical deflection.
It is not so complicated like interchanging transformers in the horizontal
output.
Good luck!

TV-collector

[Chris K]

Thanks all. I think I'll keep my eyes open for a donor although making sure it's a D chassis first may pose a communication challenge with the seller if they are not minimally vintage TV savvy.