RCA KCS 94 Aquisition and Questions

[mr_rye89]

I picked up this guy on Tuesday, very dirty but very intact. 17AVP4 picture tube, series string set, selenium rectifiers, blah blah blah....

Now my questions are:

Where does one get a NTC Thermistor that is 450 ohms cold, 9-ish ohms hot that can handle a series string of tube filaments? Mine is cooked

Does anybody know where to get a horizontal waveform coil? Right hand side of the last pic attached) According to the Sams it has a DC resistance of 48 ohms.

I do have all the knobs BTW and the model number is 17-S-6044 incase anyone wants to know.....

[mr_rye89]

The horizontal waveform coil that is. i decided to do an autopsy and found the other side of the wire. Soldered crudely but it works! Measures 48 ohms. I also re mounted the horizontal oscillator/hold coil back on the chassis, it was loose for some reason.

[mr_rye89]

I'm still at a loss for the filament string thermistor, maybe something like this:

https://www.mouser.com/ProductDetail...3uJp0Cqw%3D%3D

[mr_rye89]

Did a recap yesterday, powered up tonight. so far we have sound, vertical sounds like its running, horizontal is running (doesn't sound right), no smoke! no raster or picture though. B+ voltages are a tad high (I might increase the value of the fuse resistor) most tubes test ok, the HV rectifier seems flaky, I'll likely get a replacement before the weekend is out. When I first got my Motorola set it's HV rectifier was flaky and it wouldn't make a picture either.......

EDIT: The thermistor in the link worked well

[mr_rye89]

Kinda quiet in here.......

I changed some resistors, put a new HV Rectifier and damper in and farted around for an hour to get it to make a picture..........Turns out the ion trap was mis-adjusted. This set won't make a picture without it lined up right..D'oh!

It makes a good picture now, but I'm not watching it due to the burning resistor smell coming from it, I think it's the 150 ohm 1 watt resistor that goes between the vertical output transformer secondary center tap (or yoke) and the control grid on the vertical output tube. Vertical seems fine.

And yes the centering magnet needs adjustment

[JohnCT]

Originally Posted by mr_rye89

I changed some resistors, put a new HV Rectifier and damper in and farted around for an hour to get it to make a picture..........Turns out the ion trap was mis-adjusted. This set won't make a picture without it lined up right..D'oh!

Heheh... ion traps..

I had exactly one experience with an ion trap (although I'll be seeing more after joining this group and getting into old TV).

Back before I was even a young shaver, my dad would throw me $5 to change picture tubes in TVs for him. He had me change a B&W tube in an old RCA, and I put everything back in it *exactly* as it came out. I turned the TV on and the picture didn't look any better than the worn out tube that I changed.

When dad came back, I told him the new tube was no good. He looked at it a second and rotated the ion trap around the tube and the damned thing sprung to life.

I never forgot that, but I haven't seen one since.

Picture looks strong and linear on your project.



John

[compucat]

I have always like that particular model. I am rather fond of those metal cabinet RCAs. I have one of the eight inch portables I restored ages ago which still works great. Too bad RCA was so sold on using printed circuit boards. The heat from the tubes just does them in.

[JohnCT]

Originally Posted by compucat

Too bad RCA was so sold on using printed circuit boards. The heat from the tubes just does them in.

I can't recall any issues with RCA printed circuits, at least those in the color chassis.

I recall bad connections on tube sockets that were tough to make right because of the oxidation, but I found that replacing the socket fixed it permanently. The copper itself was never a problem.

I do recall Philco circuits having the copper roll up like carpet as soon as a soldering iron touched it.

John

[mr_rye89]

Yeah im not a big fan of old phenolic PC boards in tube gear. The ones in this TV aren't too horrible, I didn't disturb any traces either, I just cut the old capacitors out while leaving some of the old leads, I twisted and soldered the new leads to the old ones. Not pretty but better than lifted traces. That 150 ohm resistor is still running too hot, probably because the b+ is 20 volts too high, and I increased the fuse resistor from 5.6 to 8.2 ohms with little difference.

this is a cool set an it has a 4 legged base with a lazy Susan so you can swivel the whole set.

[JohnCT]

Originally Posted by mr_rye89

That 150 ohm resistor is still running too hot, probably because the b+ is 20 volts too high, and I increased the fuse resistor from 5.6 to 8.2 ohms with little difference.

Sometimes a resistor will run hot if the filter in front of it is weak.

John

[TonyP]

maybe the vert output tube has grid emission. measure the grid voltage over a period of a few minutes. does it rise? Is is already more than a volt or two positive? I think its supposed to be zero. If it is more than a volt positive, then turn the brightness down, remove the tube. measure the grid volts. if they dont rise, then its the tube. if the voltage keeps rising, could be the coupling cap is leaky. yes, new caps can be defective. most likely the tube had grid emission (aka tube is gassy).

[mr_rye89]

I haven't checked grid emission on the vertical output, I don't have test sockets but I can test for it on my tube tester I guess. The method you described sounds more accurate.

I have two 8.2 ohm resistors in series for a fuse resistor now and it brought the B+ back down closer to spec, and the burning resistor smell is gone so we'll see. This set is a good performer and fun to watch, not as bright as my '60 Motorola but that set has an aluminized tube and a runs a higher anode voltage. Now I have to figure out where I'm going to put this set........

[DavGoodlin]

Nice work, very interesting set. Was this the first series string portable?

I never saw one of these earlier, small screen RCAs other than KCS 102, a 14 inch beast with power trans. The series filament version KCS 109 which has that blasted metal shield under the big PC board. Access is the problem with RCA pc boards more than anything else.

[mr_rye89]

I'm not sure if this is one of the first series string sets, maybe. It dates from '56 or so. I didn't remove any of the boards, I just wire wrapped and soldered the new caps to partial legs of the old ones. The shields are a pain but I think they sorta keep the tubes from cooking the boards as mine are all in great shape.

[Electronic M]

Might be RCAs first series TV, but the Moto VT-71 was series string from go and it was a 1948 set.