Re-capping Raytheon... - Videokarma.org TV - Video

Charlie · #1 03-20-2007, 04:14 PM

I spent most of yesterday afternoon going thru the 1950 Raytheon porthole set. I have a few more caps to go, then clean out the high voltage cage (pretty dirty in there).

I found a modification done in the sound section. The chassis uses a 6T8 for both the detector and AF amp. For unknown reasons, someone has wired in a 6AV6 under the chassis and given it AF amp duty. I left the circuit as is... only replacing a cap or two going to the 6AV6.

Another modification I found is a .03 mfd 600 volt cap wired in between the yoke and G2 of the 16AP4. If anyone understanding theory better than I has Sams 99-14, please have a look. The cap connects at Line 4 (vert) of the yoke and at the top of C104 just before pin 10 of the CRT. I'm assuming there might have been a problem somewhere, and adding this .03 cap was a quick fix. I'm going with the hunch that I should remove this. Tell me what you think.

Thanks

***Eric H*** · #2 03-20-2007, 04:30 PM

Charlie, just a guess but I wonder if the .03@600 was added to fix a retrace line problem?

Sounds a bit like the mod that's been mentioned before.

Charlie · #3 03-21-2007, 03:05 PM

Perhaps you are right, Eric. I will leave the circuit as is for now.

The chassis in this set was TIRED! The lytics were pretty bad... seriously leaky and one open. At some point, somebody wired in a new lytic in the power supply without disconnecting the leaky one... just wired one on top of the other. Four tubes were bad... HV rectifier was open, 6T8 was shorted, and the last two were pretty weak. I was a little surprised to find four tubes with so many issues. I suppose the HV tube going out was when they finally retired the set. A 10-watt resistor doubled in value, and while I haven't gone thru the rest of the resistors, I'm sure I'll find many off spec.

As of last night, we have a heartbeat! I ran it for a little bit with the high voltage disabled, and then plugged in the HO Tube and got a picture... and no unpleasant surprises.

The screen shows signs of more work to be done. The picture is a bit weak, retrace lines across the entire screen, and no control of the brightness (although threre is good brightness). Guess I'll poke around in the video amp area later. I suspect resistors. Regardless, I was glad to get a picture out of it.

High voltage seems good and steady. The Sams does not give any HV info... but I'm getting about 12KV and I'm sure that's good for a 16" CRT.

I would have posted a picture, but, I can't find my camera. I'll look for it tonight.

polaraman · #4 03-21-2007, 05:56 PM

Charlie,

You finally made it off the ship! Glad to see you are working on that set. I almost drove back to Texas to get it. I'm glad you got it. It is really cool. Gonna replace the Tv at the cabin?

polaraman

Charlie · #5 03-22-2007, 01:09 AM

Actually, I've been home for a month! I go back to work 4-13 I think. I haven't really been online much... a few computer issues have been limiting my online experience. It won't be long before I'll be needing to upgrade.

No, I don't think this set will replace the Diamond D. I watch the DD on a regular basis, and like the picture the picture it makes, so I plan on leaving it where it is. Also, I don't think I can get used to watching this Raytheon on a regular basis since the screen is a complete circle... end up missing a lot of the picture.

I found the camera earlier... it was under the seat in the Duster. I'll try and get some pics up here tomorrow.

wiseguy · #6 03-22-2007, 06:10 AM

do they let you bring things to work on during your off days on ship?

terry

Charlie · #7 03-22-2007, 01:02 PM

Okay... here's a couple of shots of what I've got so far... weak pic, retrace lines (which are kinda hard to see in these photos), and no brightness control.

On the other hand... I've got good vert and horz hold, sound, and it seems to pick up stations pretty good (considering I'm out in the woods right now).

The set has an interesting tuner. A drum of screws rub against a cam and drive six plungers up and down into a set of coils. I haven't seen one like this before. Because of it's design, each click of the tuner is more like a huge "clunk" and feels more like an industrial switch that turns an entire neighborhood on and off!

Terry: Years ago, I used to bring projects with me to work on while on board ship. I can remember re-capping a TV, a radio, and a portable Magnavox 3" reel-to-reel. At one point, the chief engineer hung a sign on my door that said "Electron Room" and it stayed there till the ship was sold for scrap. Now days, I don't bring anything to work on since I'm usually flying out west or to Panama to join the vessel.

Charlie · #8 03-22-2007, 01:06 PM

Those pics didn't upload very well... they're actually a little better than that. It appears they got compressed some along the way.

polaraman · #9 03-22-2007, 04:07 PM

Charlie,

I see you are watching the Bewitched DVD.

polaraman

cbenham · #10 03-23-2007, 01:39 AM

Quote:

Originally Posted by Charlie

I spent most of yesterday afternoon going thru the 1950 Raytheon porthole set.
I found a .03 mfd 600 volt cap wired in between the yoke and G2 of the 16AP4. The cap connects at Line 4 (vert) of the yoke and at the top of C104 just before pin 10 of the CRT.

I looked at 99-14. I think someone added 'vertical retrace blanking' to your set. The .03 cap probably should have a resistor between it and the yoke connection. That's a very high voltage pulse to couple to G2.
The pulses getting through that cap to pin 10 could be 300-600 volts,
probably too much for it.

If I were going to add vert. retrace blanking to this set [I have the 12 inch version] I would feed it from the yoke through a *resistor*, THEN the cap to pin 10, but I'd probably start by finding out what value resistor to wire in by clip-leading a 100K pot in series with the cap and watch to see when the retrace lines go away while I twist the pot, but remember the *HV* pulses! They don't feel so good through your fingers. ;^)

Best luck,
Cliff

Charlie · #11 03-25-2007, 02:09 AM

Rich, I like looking at the screen with Bewitched playing because the older shows used good lighting and a contrasty environment which shows a good picture on a B&W TV. Also, it seems while making these old shows, they kept in mind that some people were still watching porthole sets from 15 years prior. Even in scenes with two or more people, they're all seen on the screen. You don't really lose anyone in the corners.

Cliff, thanks for the pointers on the retrace lines. I'll dig around for a 100K pot and try your suggestion. Right now, I'm thinking I still have retrace lines since the brightness seems to be way up (no control of it) and I think once I can turn it down some, those lines will fade away.

As far as brightness control, it seems the pot fails to function correctly. I thought I had checked it earlier, but, I either didn't or made a mistake.

I haven't played with it in the past couple of days due to a visitor, but I've things got a little better right after my last post. In the IF section, I found the resistor on pin 7 OF ALL FOUR I.F. TUBES had gone up considerably. Three of them were supposed to be 82 ohms... and they gave me readings of 200-250 ohms. The last one was supposed to be 68 ohms and instead read 125 ohms. Being that EACH ONE was off, i thought I was somehow making a mistake. I even got my other meter to double check. After changing them, the picture got stronger.

I also changed about two dozen other resistors that were 20 percent or more off spec. A 5 watt resistor in the damper area jumped way up in value. Things are very gradually getting better.

I found another modification... someone tied a couple of resistors between the tuner and IF... one of them going to ground. Before realizing these weren't supposed to be in there, I was chasing funky readings in the IF and AGC. After isolating the two sections, I found the funky readings only in the IF and started digging around there... when I noticed two resistors that weren't in the schematic. I removed the resistors and didn't notice any change in the picture.

Over all, I'm pleased that things are gradually improving. This set must have had a lot of hours on it. My Diamond D was the same way... lots of resistors to change!

Charlie · #12 03-25-2007, 08:28 PM

Things really fell into place today. I found a few more resistors that were 50% off spec, and then I gave the brightness pot a shot of spray... which was all it needed to make it work again. Now, I have good brightness control and turning it down some made those retrace lines go away. Things are lookin pretty good now!

I still plan on taking Cliff's suggestion of installing a resistor in that retrace blanking circuit, but first have to drive back to town and dig thru my stash for a pot.

Here's a couple of shots from this evening... much better than the other day.

jpdylon · #13 03-25-2007, 09:13 PM

Great screen shots Charlie! looks like its coming together well