The inevitable callback on RCA 17PT8072
 

I got this KCS109 set years ago for $10 and never had (still don't have) the Schematic:sigh: If you have it, please PM me. I need to do it right this time.

Attachment 176895Attachment 176896

I even have two Sams 392 and THIS folder is missing from both!!!:thumbsdn:
It must be RCA's only late 50s set with series filaments and doubler power supply with two seleniums.

A friend of mine turned a small room into a bar and I told him I had the perfect TV:yes: It worked OK for 3 years but is now showing the signs that I did not finish the job, barely starting it. The electrolytics must be replaced. The major symptom is the poor AGC and sync as it plays longer.

Since I had no schemo, I bluffed it by testing all with my EICO 950 and replacing only the obviously bad caps. Someone had repaired the power supply, changing the 3-section cap and subbing in silicon rectifiers, I had to trust and could not check this for OEM parts accuracy. The set did work, kind of, so I left it alone and just worked on the PC board, eliminating the bumblebees. I need the schematic to do the rest. It should be a hit this Christmas because it embarrassed me last year, rolling and tearing.:scratch2:

In addition to bumblebees, I think I see some "maroon drop" caps in there. They are brownish or maroon and look like modern orange drops except for the color.

Those are also candidates for replacement. My RCA CTC-7 had terrible sweep problems and other issues before I replaced them. It magically made a fine picture after all of the maroon drops had gone bye-bye.

Ditto, even more so, for any remaining paper caps. If the values are printed on the cases, you don't need a schematic to replace those. If you want this TV to work reliably for an audience, I would not even waste time testing those.

Phil Nelson

That is the way I used to work on vintage TV for years. I gave up on Radio Shack and once all the parts jobbers closed (except Moyers, 2 hours away), I assumed the sources for caps over 200 volts were gone. I did not know about places like Justradios so I tested all caps, replacing what was bad. I kept many late 60s RCA and Zenith chassis around for the orange and maroon drops.
Sorry to hear the maroons are suspect, they used to be a safe bet. If I ever get time to recap my CTC11, I will be felling pretty good!

I still need the schematic.

ETF does not have a KCS-109 in resources. ET circuit digests do not even cover it and my extensive RCA library is missing it as well.

Its time I finished this up and returned it.
 

Getting back on this project, I replaced all the Electrolytic and Paper caps.
I noticed a tube socket missing as I got a closer look..
http://farm3.staticflickr.com/2806/1...92326cc23e.jpg
KCS109A pcb 1 When I saw what makes the KCS109A special, a missing 4CB6 IF tube, it confirmed this set was sold in a strong-signal area, as a personal label on it had a Philadelphia address, one neighborhood away from the transmitters

http://farm4.staticflickr.com/3741/1...95644fd865.jpg
KCS109A pcb 2 Has anyone seen this? I got the manufacturers' service manual and this "printed" is labeled "C257".:scratch2:
http://farm4.staticflickr.com/3804/1...f350f2c06e.jpg
C257 "printed" instead of a 4CB6 like the KCS109C and D

Looks like they used a couple of adjacent parallel traces to form a capacitor to bridge the IF signal across the deleted tube...A very interesting approach!

It was not uncommon for manufacturers in the day on cheaper 'stripped down' models of sets (particularly stereo consoles) to delete sockets from PCBs and bypass signals and other electrical paths across the old socket pins....Though usually it involved soldered on wires or components, and or PCB traces strategically broken at the factory, rather than a alternate PCB foil pattern...

Heh. Quite a 'gimmick'.:tongue:

Yes Sir , I am familiar with the "gimmick" capacitor from my tube FM radio work . It would usually appear as two wires lightly twisted together but of course not electrically connected together . An easy way to get a couple of picofarads without an actual component and somewhat adjustable by twisting tighter or loosening the twists . A neat way to accomplish a desired result :)

Not to go too far off topic, but speaking of unusual traces . . . when recapping my CTC-4, I noticed these two squiggly guys:

http://antiqueradio.org/art/RCACTC-4IFBoard.jpg

??

Maybe that's commonplace in PC boards, but I don't work with them often.

Phil Nelson

I suspect it is an inductor?

Could be a delay line

The luminance delay line is a thick cable-like component mounted above the chassis. The schematic shows two components (L62, L64), described as "filament choke," between the filaments of the IF tubes. I haven't tried to sort things on the foil side to determine whether these squiggles are indeed the chokes. Filament choke is a new concept to me -- maybe intended to filter AC ripple to keep it out of the video signal?

Phil Nelson

I had a simular model that had a transformer power supply and a 5U4 rectifier. I lost interest in it, when I discovered, that someone hacked up the PC board, in some kind of a repair attempt. :thumbsdn:
Some of those RCA's were pretty impressive, buy miserable to repair.

They're RF chokes intended to avert spurious coupling problems (ie., feedback) via the heaters.
Never heard it explained that way, but presumed that's what they were for.

Delay line was my first guess too, then I realized the tight coil-like back-n-forth would probably have an inductance. Give 'em props for ingenuity.

Often, series heater sets have bypass caps at and small chokes between filaments on the tuner and IF tubes

The lesson for me is that, at one time, I could "restore" a set like this by replacing only what is bad and it would be fine.
Many parts failed prematurely and thats what you normally see replaced (usually long ago) in a set of this vintage.
Now that these metal RCA's are coming up on 60 years, any and all paper and electrolytic capacitors are unacceptable.
Unless there are other issues, replacing these parts in total will almost guarantee a set working as designed.

The replacement rectifiers and 10 ohm - 15 watt series resistor deliver exactly 260V B+ from the doubler supply at 120 volts AC.
My line voltage runs high at 122-124, so it's SOP to add a thermistor (motorola's tube sentry), fuse and increase the B+ and filament drop resistor values.
Ive spent the last few weeks using it in the shop and each time I run it for 5 minutes or 3 hours, its without issues:yes:
The contrast control doubles as the AGC control in this model, another interesting effect :scratch2: of running everything through the video amp as if it were a third IF.
http://farm3.staticflickr.com/2863/1...00441826b1.jpg
Contrast fully up

With a Winegard DTV converter, the sound is clear and does not buzz with text on the screen.
A tweak on the sound take-off transformer took care of that.(after the video amp, not just the detector)

The yoke cover is a disaster but at least the rings are stationary. the caps are all new but I did not stuff any:sigh:
There is only so much you can do before any further restoration of the project is taking time away from really interesting projects.
Restoring a 630TS with those details is almost expected, but on this set, performance and exterior appearance count the most.

Despite the weak 17CDP4 CRT, it still looks good for regular watching. Of course , I would NOT use the B&K 445 to rejuvenate it anyway.
All I did originally was let the 8.4 volt filament cook for a few minutes at 12 volts, with a bit of improvement.
These 110 degree deflection picture tubes were certainly no improvement over the 90 degree (longer) tubes.

http://farm6.staticflickr.com/5514/1...c1d1f6dd90.jpg
CRT tests not so good
http://farm6.staticflickr.com/5477/1...4b29dd7a44.jpg
After 5 minute warm up [url=http://www.flickr.com/people/100376096@N02/]

One last thing, I thought I knew this set from somewhere. Its funny how Hollywood sprayed everything on the back of the set gold.
Back in the day, I just noticed there was no antenna connected.:)
http://farm3.staticflickr.com/2885/1...9482920d29.jpg
LAVERNE_SHIRLEY 17PT8074