checked it again, dont know what the deal was with the eye tube cap tester but now working .001uf on two different ranges.

very interesting. The 12" tube I had did not have any dag on it at all, so I grabbed a 10Bp4. the cap value was barely readable .00001 but it did null there that vs the .001 geez.... and the resistance reading was also very different, I get 800ohms about 3"apart on the new dag, vs 15,000ohms on the old dag. the old dag is clearly thinner than the new. I dont have a NOS tube to compare with.

http://www.shinjo.info/frank/sheets/127/1/12LP4.pdf

the 10bp4 as min 500pf max 2000pf.


So it looks like my recoated 12LP4 at 1000pf is in the right range, and my old 10BP4 with its worn dag is def outside the min as it was more like 10pf vs 500pf min


I can see I am going to have to redo the dag on the old 10bp4 just to see the improvement in capacitance as a test.

Good deal. That's half the price of Aerodag G, which is what I've used before.

http://www.grainger.com/Grainger/SLIP-P ... cant-1WVK7

http://www.tedpella.com/SEMmisc_html/SE ... hor1349940

Either way, one can lasts a long time!

Phil Nelson

Phil, curious about the conductivity of the the aero vs the slip. If you get a chance pls get a ohm reading of say 1" of covering. I suspect it has a lot to do with just how thick the coating is, I know I put a few coats on mine, then knocked it down with a green scrub pad (it was getting pretty ruff like bad overspray) then shot a couple more for a satin like finish.

I think on the next one I will measure the capacity and resistance as I go. Should be a nice experiment.

I was also going to rig up an old LP turn table with a box over the spindle and put the CRT on top, then spin it at 16 while holding a constant spray, again just a fun thing to do, not needed of course.

I added a .047 cap between the vert out green lead and the cathode of the CRT and a 3.3 k resistor between the center of the pot and the CRT cathode. It was very easy to do since there was a term strip and they were right next to each other. I tried different caps and some resistance in series but the .047 was perfect. I gives a 35v pp spike on the cathode (the video is coupled to the grid, the cathode sets up the brightness thru a voltage divder pot). I can't think of any harm this can cause except maybe to that pot.

I can now set the controls to any setting of brighness and contrast and there is not a hint of retrace. I will tag this change for any future techs that may encounter this set.

I tweeked up the discriminator transformer so the audio would max out just as the fine tuning peaked. Messing with the brigthtness I noticed that at very low levels the top of the pic was a bit darker, vertical blanking from the cap addition, so I went back and changed it to a .033 now the shading is barely noticable. You have to have the screen almost completely cut off to notice any change in shading. You can see some retrace now but only with the brightness fully advanced with low contrast, so the pic looks bad long before the retrace lines become an issue. So with this setup you get a much broader range of brightness, better low contrast scenes before retrace is an issue.

after more playing I am now at a .022 and a 33k seems about perfect. This by the way is the same values used on an old capehart.

Now that its all working I went out to check on the cabinet, Bill C was right, its metal, I sure thought it was bakelite as is seemed thicker and heavier, but I know bakelite is not magnetic so metal it is. I feel better about painting it now.

You had me going... thought you'd found a very rare Bakelite T-120.

there was a lot of paint fleck everywhere including on the CRT plastic cover. got it all cleaned up with some thinner, I was worried about it reacting with the plastic, but it was ok. I am assuming its plastic, after that mix up on the cabinet, I am not so quick to say for sure

I would like to repaint the whole thing, its a mess, but that would include the front where the control knobs are. Any ideas on how to reproduce the various markings (volume, on of, horz vert etc....

At one time, you could purchase generic TV decals, which were very close to the typeface and size used on some of the RCA's, DuMonts, and other brands of that vintage. Try checking AES and Radio Daze.

Almost positive the face of that is laminated or tempered safety glass, RCA didn't use plastic windows until much later.

Radio Daze sells some water slide decal sets that might work, they do have a couple TV specific sets. Book and stationary stores used to carry dry transfer lettering sets, but I haven't looked for years.

http://www.radiodaze.com/category/211.aspx

good info. I was hoping to find some dry transfers, not that I have ever used them before.

I was messing with the modulator, the sensitivity of the set is excellent. with a pair of rabbit ears I can keep the BT450 way low and still get perfect reception.

the osc tube is no longer a problem, the cleaning of the tube pins took care of that, it used to be if you touched the tube it would go off (6J6).

the leather belt was broken, but I am attempting to glue it. Right now I just made up a loop of dial string and looped it 4 times, works perfect on the fine tuner.

I just use an O-ring about 3/16" or 1/4" diameter to replace the fine tuning belt, and remove the idler and spring saving those in a small envelope for future use.

I was going to try that Dennis, but I had the dial cord (and not an o ring) and it works fine. The belt glue worked but it was just too tight a fit so I left the dial cord fix in place.

dont know if I mentioned it but I ended up with a .01 and a 33k resistor. The vertical shading was is still evident but only if you are staring at a dark rastor and really looking for it. the retrace lines are a non issue with the fix.

all that is left is the 2 650 power resistors, after that I will prob button it up until I get motivated to work on the cabinet.

I must say this is by far the best B&W set I have as far the quality of the picture goes. the detail and grey scale are fantastic.

That horizontal circuit is called the synchroguide. It was used in pretty much all RCA sets from the 630 onwards through at least the mid 50's (my 1955 RCA CTC-4 color set even uses it), and was adopted by a number of TV brands in addition to RCA. If you collect pre-1960 sets then you have probably encountered it more than once.

Tom C.

my solution to the voltage divider on the back.

removed it after wetting down with some tuner lube to keep the asbestos from fraying. I mounted some single term strips by drilling a hole and using a self tapping screw. the term are mounted such that they go thru the factory holes in the chassis where the orig terms came thru. I used the orig metal guard to mount them so I had to mark the mount locations before drilling. I wanted the terms to exit as close to the dead center of the hole as possible when the metal guard/mount is attached. I ground of the tips of the self tapping as I did not want them to poke me from the outside.

next I wired up two resistors in series a 350 and 300 5 watt square sand resistor. used a pigtail on one and a short lead on the other. next I mounted them to the term stips so they would be clamped between the chassis and the mount, nice heat sink as well that way. There is plenty of room so they will not short out, but I slipped a couple pieces of heat shrink over the completed assy anyway, so only the tip of the term strip would show thru.

Mounted it in place the wires and resistors that attached to the orig fit perfect as they should since the term stirp was in the exact location of the original.

works great. I sorta wish I had done the 850 ohm section the same way, but I had already mounted it up on an existing unused term strip under the chassis so I did not want to go make work for myself. Sorry for no pics, but my camera is MIA...

finally got my cam back. here are some pics. some obvious problems present themselves. There is a shorting hazard between the exposed wires that interconnect the series power resistors (300+350) for each of the 650 ohm sections.

If someone were to drop a screw or other conductive object down around the gap between the metal plate and the tv chassis, it could short the exposed wire to the chassis. Likely? not, but possible certainly. I could have minimized this by using a single 10watt resistor but it would need to be the same thickness as the 5watt to fit well. That would elimnate one exposed connection. Next is the exposed part of the term strip. I could have used some heat shrink further down the term stirp and on the wire from the resistor to the term strip and prob completely covered all exposed wiring. Frankly I just was not thinking along these lines, until after it was all done and installed. I am now not happy about the under the chassis 850 ohm that was orig part of that strip. So the new plan is to see if I can come up with the correct resistors and do it over again, this time with an eye toward the shorting hazard. I was thinking about just dabbing some silcone over the exposed parts but that seems like a hack thing to do (more than this anyway). Sorry for the one blurry shot, I will get some better ones when I pull and redo the strip.

actully the hot part of the terminal is inside the chassis so that is not a problem, just the interconnect of the series resistors and the short part of the resistor that lead inside to the hot part of the term strip is the problem.

I hope to remove the metal clips that hold the front face plate in so I can work on it and clean up the brass trim some.

I am considering spray paints, any good recommendations on paints? some kind of dark brown that is easy to use?

I presume a good primer would be needed as well. Its been a while since I have done any spary paints, but I do have a spray gun (big for car painting), have not used in in 30yrs but seems like it would make it easy to get good coverage with little overlap needed.