New Project - RCA 8PT
 

Today a package arrived, containing a very nice little TV, the RCA 8PT, black, with a swivel stand. It's in excellent physical condition, and my goal is to get it into excellent electrical condition as well.

Opened it up, cleaned out dust, tested the tubes... it needed only one tube, a 6U8, curiously the only non RCA 6U8, a Japanese Channel Master, was bad.

Turning on the TV it gets a nice bright raster, and good sound, but the horizontal hold can't be dialed in.

One symptom worries me a bit, probably due to ignorance. With the Horizontal frequency control at a low frequency (I can hear the flyback), the out of sync image is nice and bright. As I turn up the frequency, it hits a point where the image horizontally collapses into what looks like a modulated vertical stripe, and the screen gradually goes dark. I think I can hear zapping sounds in the flyback, or maybe the frequency is just all over the place, but whatever it is appears to be killing the high voltage. Turn down the horizontal frequency, and the image comes back, full brightness, and the high voltage appears to be restored, but sync is impossible.

I am going to replace all the capacitors in the TV before I worry too much about the lack of horizontal sync, but the possibility of a bad flyback is a bit worrying. I wonder what the experts think.

I have to say, it is a nice contrast to my other vintage tv, in that moving it around can be done with one hand!

Looks like we've got another spammer!

"china wholesale". Yeah,that's just what people on a *vintage* tv site want...Chinese crap!

Spammer banned.

...

Neat little sets, although the innards are tightly packed. This article has a link to the RCA factory service manual, and a few notes that may be helpful.

http://antiqueradio.org/rca16.htm

Phil Nelson
http://antiqueradio.org/index.html

My best guess would be the .047/600v paper cap in the boost circuit...And yes, I have also heard odd clicking noises when the frequency is way off and "squigging" (if that is the proper term). There are only about 4 paper caps in the horiz section (2-.047s, 1-.022 and 1-.22), I think that I would do those first and re-check the performance,
jr

Thanks all for the input!

I think I better go against my desire to see a picture on the screen now, and wait for all the capacitors to show up before I continue on. I'm happy to know this doesn't mean the flyback is suspect, at this point. In addition to the symptom mentioned above, the B+ is about 160, and should be 216, so fresh electrolytics and ditching the selenium rectifiers sure looks like it won't hurt.

Phil - your website is great, I remember reading about your TV several years ago when I used to go on rec.antiques.radio+phono. That's where I first became aware of this model. I printed the service manual from your website about a week before the TV arrived, to have an idea what to expect. I have to say I am surprised by how small everything is... even the controls are tiny.

I cleaned up the case with a toothbrush and warm water... it looks nearly new, although maybe it could be a bit more shiny. The only defect is the antennas are broken.

finally got my order in at mouser - 39 caps and two diodes. If it takes half as long to install these as it did to order them online I'm doing well :)

It's amazing how much grime gets trapped under safety glass...

Yeah, well, you gotta remember that l'il guy is 51-54 yrs old, & I'd about guarantee SOMETIME in its life it was around a smoker or 2, a few pets, & prolly some kids...Too bad these things can't talk-I'd LOVE to hear some of the stories they could tell...

I have one of those I have been using regularly for ten years now. I did a full recap when I got it and it works great. These are some of the best built vintage portables around, transformer powered, no printed circuits, all metal cabinet, etc. Once restored, it will reward you with years of viewing pleasure and it is small enough to use and display anywhere. Take your time with it and it will be well worth it. Let's see some pictures along the way.

Photos 1 of 2
 

As requested - here's some photos. Set is basically as received from member Eric H, aside from some light dusting and cleaning. As you can see it is in excellent internal and external condition!

Photos 2 of 2
 

You can see where I damaged the vertical hold knob a little bit when I was putting the chassis back into the case. Luckily it just cracked off a piece, which I recovered, and it didn't crumble, so I can glue it back together. These knobs are very delicate! When you separate the front and rear halfs of the chassis, getting it lined up again so everything lines up is a bit critical. Mine is one of the later models with safety glass instead of plexiglass, so it is very easy to clean and free of scratches.

Those small knobs are often missing, probably more than half my 8" sets are missing them entirely.
Someone should repro them, shouldn't be too hard provided you can come up with a pristine one to make a mold from.

I have (had) 12 of these little guys, I think every single one of them would at least display a raster without anything being done to them, usually the Horizontal won't quite sync up, that's pretty amazing, only one has a bad CRT , way better odds than most sets.

That is about the condition mine was in when I first got it. Mine produced a weak picture with no sync when I got it. Since restoration it works like new and the CRT is strong and bright. It would have been nice if RCA had used an aluminized tube. I used to lament the lack of UHF on these sets but since the digital switch over it is no longer an issue. They make great daily watchers. It is a lot of work disassembling that cramped chassis and getting to all those paper caps but the results are well worth it. I am surprised RCA put so much into this set considering they were using PC boards in their much more expensive products.

Wow, a portablel with a transformer!

I have not seen one of those in person, but it just amazes me how all that could be crammed together like that!

The 8" Emerson with the radio built in, is also transformer powered.

Yep! those little rubber knobs are the first to go, they get brittle and break off in chunks. On my childhood set, I replaced them with short pieces of black insulation in about 1959. Today I just cut short chunks of silicone tubing (model airplane fuel line) and slide onto the knurled shafts. Second to go was the power cord, where it enters the set.

Your set is looking great! good luck with the re-cap job!

jr

3 of 'em have managed to find me-Plus one of the Emerson AM radio/TV combos, which uses the same CRT. Oddly, the best cosmetic-condition one-a sort of grey-beige version-has a CRT that's about shot.

Sandy, Is that emerson am/tv you have got UHF? Ive got one here with no knobs and i need to see pics if its the same ..

Steve

No UHF.

Thanks for all the comments! I've been trying to be extremely careful with the set.. was annoying to crack the little knob, but such is life. The plastic antenna mount is broken on mine, I'm going to try to repair it with epoxy or JB-Weld before I start to search for a replacement. The quality of construction is amazing... even after looking at all the photos on Phil's website, I can't say I was prepared for how small it actually is! The only other place I've seen the same size and type of potentiometer, is in old 50s Motorola two way radios... the type with submini tubes. Makes me wonder what modern electronics would look like had the Japanese never become involved in things.

About 75% done replacing capacitors - wow there's a lot, and wow is it small! Work is going well though! There is an error in the parts list, in the RCA manual. C164 is listed as 0.001uf, but in the TV and on the schematic it is really 0.022. I paralleled two 0.01's, couldn't find any 0.022's locally.

All done except electrolytic can. Gonna restuff it this week, but it isn't warm in operation. TV picture looks awesome, it's sharp, with great geometry. Not perfect, but very close!

Sound has a lot of buzz when text is on the screen, but otherwise is good. I suspect there's not much I can do about this? It's nice to see this little guy alive!

Have a couple more observations about this little TV.

1) The problem Phil encountered with the picture being tilted, seems to be because the yoke is held in place with spring pressure, and rotates on its own a bit when the chassis is installed back into the cabinet. It can be corrected by removing the control door, and inserting an insulated flat blade screwdriver into the tv with the guidance of a flashlight, and using it to move the yoke into correct alignment. It seems like every time I move the TV, the picture gets a bit tilted.

2) The TV is fairly poorly shielded. My cable box puts out a signal on 3, and since there is also a broadcast station on this channel, the interference ends up as lines on the picture. Using a VCR as a video modulator gives me a nice crisp picture.

3) White screen or text puts an unacceptable amount of buzz into the audio. Can anything be done to help this?

I may be remembering wrong, but I think that there is a large Phillips head screw on the outside of the yoke housing near the bottom that pushes a collar with fingers against the back of the yoke to hold it in position.
jr

Yes there is, also the plastic yoke covers are nearly always distorted on these, enough to lose the centering magnets in some cases.

When I rebuilt one I discovered the long metal shield around the neck of the CRT had to be in place or it wouldn't get a raster, possibly the Ion trap was weak or just so tiny it wouldn't work without the shielding.

Originally these had a long stiff piece of fish paper attached to the Ion trap and extending out the back far enough to adjust the trap by removing the rear cover, this is often to brittle to use after 50 years and either has to be replaced or you have to adjust the trap with a non ferrous stick of some sort.

BTW Max, I still need to look for the rear cover for you, if you can't fix the antennas you'll need it to cover the hole. Remind me if I don't contact you soon, I forget things easily these days.

I've had the TV on all afternoon... it seems the buzzing has quieted down to such a low level I almost don't notice it since the TV has been really fully warmed up for hours. Figured out my CRT computer monitor is interefering with the picture on the RCA. Easy to solve that, I don't plan on keeping the RCA in my computer room anyway! So far I've been operating it with the antennas down, but Eric if you do dig up a rear cover I'd like to get ahold of it. No big rush, it's working fine as is.

The fish paper is intact on my TV, but haven't had a need to adjust the ion trap yet - picture is good and bright as is. I'm getting used to life in black and white!

I have had many 50s sets that buzz when white lettering is displayed on the screen, and others that don't. It seems that I have read a technical explanation as to why this occurs, but I don't think that it indicates any problem in the set itself. I wonder if slightly adjusting the AGC control might help? It would be worth a try and certainly can't hurt anything. The portable might not even have an AGC adjustment. The main thing is noting approximately where the original setting was for what I call backward reference. LOL!

Yes.

http://antiqueradio.org/art/rca1619.jpg

Many old TVs buzz in scenes with very high contrast. Aligning the sound section can help, but on some sets you may never eliminate it entirely. Backing off the contrast will reduce it. Sound buzz is more noticeable now than in Ye Olde Dayes because contemporary TV programs are littered with constant text crawls along the bottom, animated logos, etc., etc.

Phil Nelson

Thanks guys!

Removing the antennas from the rear strongly improved the picture quality. They have an internal mechanism which disconnects the antennas themselves when they are fully retracted, but it wasn't working, which allowed a lot of interference to get into the TV. Removing them and adding a terminal strip made a big difference. Now I am getting very sharp focus and can see all the scan lines.

I've noticed a new problem, a bit more subtle, There's vertical stripes on the left side of the screen. At first I thought it was screen burn, or gas in the picture tube but when you turn the contrast all the way down, and brightness all the way up to get a full raster, the horizontal hold control will shift the stripes back and forth. Attached are a couple pictures. I still haven't restuffed the can filter cap, but all other paper and electrolytic caps have been replaced.

Check the filter cap for the G2. Doogie

You mean G2 of the CRT ?

I think this is a 5uf cap, part of filter can. Will try this tonight.

It is probably a 0.1 – 0.5 mfd cap. At between 400 – 1000 vdc. It will not be a can. Lookup up your CRT type number on Google and follow the wire back to the chassis and find the first cap to ground. Doogie

Ah.. in that case I would have already changed it. Will verify that the value is correct.
Schematic says G2 not tied to ground through a cap?

That could be true. Rectifiers were very expensive in the old days. Check caps in the yoke circuit. Just because you replaced them does not mean there good. Do you have an ESR meter? Good luck. Doogie

It could be a dynamic thing.

Rebuilt filter capacitor can. First one I've ever done, it was a lot easier than I was expecting. No impact on this problem, but now all electrolytics are new.

Attached is the schematic so you can see what I mean about G2

Looks like ringing in the Damper circuit, have you tried adjusting the horizontal drive coil or the width?

Just for kicks tried subbing the 6CG7, 6BQ6 and damper one by one, to no effect - all were good.

Horizontal drive doesn't seem to do much at all. Width I need to find a more appropriate screwdriver to adjust... it's got a slot in the end of a long threaded shaft, and all of my miniature screwdrivers seem to immediately slip out of the slot.