Issues on an RCA KCS-47 C
 

This is the project I've spent the last six weeks on. Ugh.

This set has had a TON of work done to it at some point in time. I'd say about half the capacitors in the set were Sangamos, the power transformer had definitely been replaced as well. Someone did some sloppy work with the line filter arrangement, which I cleaned up. I did the usual complete re-cap of the set, good tubes, etc. Only thing that I noticed was one cap value that was way off, someone replaced one of the vertical .047 @ 1 kV with a .005 @ 1.6 KV :headscrat , so I replaced with the correct value, thinking that the last time this set worked, it had some wildly keystoned picture.

The one thing I did have to do was short the power switch with a soldered jumper, as it turns out, the switch was shot.

Anyway, bringing us up to today. Powered it up for the first time on a variac. At about 85V or thereabouts, tube filaments all lit fine, no smell, no "earth shattering kaboom" (lol). I couldn't her the horizontal oscillator running, either....but there was a buzz in the audio. After a few minutes I goosed it up to full power to see where we're at.

Although there was no static in the sound, I could vary the buzz in loudness with the volume control. No raster, and a minute later, spotted a faint blue flash from the HV cage. Powered it down immediately. Figured that if there's some arcing going on, I better see what's happening.

I removed the cover on the HV cage, and powered it up once more. It appears that there's some arcing going on UNDER the chassis, in the flyback area. I didn't remove the chassis again this evening.

Before power up, I checked all of my connections, all of my solder joints, as well as my capacitor placement against the schematic. I've heard that these sets are absolutely horrible for reliability, but I'm curious what those who are more experienced than I am (which is most of you) have to add here.

Um....help? :(

Shorted fly? Maybe measure HOT cathode current while running it up to full voltage, see if it shoots up sky high?

Although I haven't restored a KCS-47 or have any experience with them, I do have a couple spare chassis in case you need any parts.

Didn't Bill Cahill (hope I got the last name right) do an EXTREMELY long thread over on ARF about a set with this chassis? I hope I have the chassis number wrong or that you have a better example of that set than him as that thread made the set he was restoring seem like a nightmare. After initial restoration work there was tons of trouble shooting and lots of new problems creeping out of the wood work as others were being fixed.

check the door knob cap , i restored one of these sets once and it caused i think a simular problem to what you described.

mike

Have been using my KCS-47 for 10 yrs or so and has work well. Every once in a while something would blowup but all in all it's been a good set.
Bill C have mentioned that the 6W4 can take out the power transformer though a filament to cathode short. Perhaps that is why you have a new power trans. Not a bad idea to run a separate filament trans for just the 6W4, I did. Luckily RCA made a bunch of those set is parts aren't too hard to come by. Don't know about the doorknob cap as mine will work without it. The flyback on this set mounts about 4 or5" above the chassis on the phonalic board. Maybe a bad 6BG6 socket??
GL
Terry
ps Are you putting the chassis back in the cabinet when you are testing it?? If so you got to make up some cables and put the chassis on top of the cabinet.

Bill Cahill informed me that someone in the past used a cheap and wrong replacement transformer on this set. He's seen this happen before. Whoever it was, didn't snip the jumper on the damper tube (which is mandated when even attempting this), and that basically, a cascade failure must have happened the last time this set was tried back in the late 60s or so.

He told me that basically, the chassis is junk. Fortunately, I've got another chassis to swap components and tubes to.

(sigh)....all that work :(

KCS47 chassis.
 

IIRC, that was the chassis, that RCA first used intercarrier audio in mid-production.
I always considered that model, a dog. :thumbsdn:

Mine appears to have had intercarrier added somewhere other than at the factory. I started on it in '83, someday I'll drag the chassis out and take it to the final production rev, but the KCS-68 beckons, as do the 8, 14, 17 and 21-inch metal cabinet ones!

In one of the Riders volumes, it shows the proceedure to convert this chassis to intercarrier audio.

Why does everyone hate these sets? Mine has been pretty good over the last 10yrs or so.
Terry