No line transformer near the CRT.

Tomorrow I should have my HV probe for my VTVM. Only then will I know what kind of HV I have.

I have the same model Knight-Kit VTVM, bought and built in 1962. I never had the HV probe.
The meter still works great. :thmbsp:

Cool! The probe is the Knight-Kit probe for the KG-625. :music:

By the time, I needed a HV probe, I ended up buying a Pomona HV probe. It was the most common at the time. I mainly used it for color sets. :thmbsp:

OK everybody.

I got my HV probe today and assembled it and hooked it up to my KG-625 VTVM. After a few minutes warm up time for both the TV and VTVM, I zeroed the VTVM and measured the HV at the door knob connection of the HV lead going to the CRT. 12Kv. I then measured at the CRT, 12Kv again. So I'm getting 12 KV at the CRT with the "stock" assembly.

OK, I got a NOS Westinghouse 25DN6 and tried that instead of the 25CD6. I now have 14Kv! 2Kv by just using an alternate tube! This measurement was with the brightness turned all the down. At normal viewing levels I have 13.5Kv.

Still very unfocused.

I boosted the B+ by 10 volts and picked up another 1Kv. With B+ from 124 volts to 134 volts I get another 1KV volts from 13.5Kv to 14.5Kv under normal viewing brightness.

I did change the original probes with an Eico Uniprobe, much more convenient.
About 20 years ago, I replaced the "C" battery and rechecked the calibration.

I found the focus problem...most likely.

I pulled the base off the bulb and the focus wire was broken.

http://i1060.photobucket.com/albums/...pstmnupcxg.jpg

Unfortunately, I broke a filament wire in the process.

http://i1060.photobucket.com/albums/...psvonnrthn.jpg

http://i1060.photobucket.com/albums/...psfmlub3rb.jpg

It looks like they broke flush...
If you can CAREFULLY chip enough glass away from the leads to have something to solder to then you can use the really fine phono hook up wire Rat Shaq sells toconnect to the stub....I've had success with that method, but it takes a high watt iron and speed to get a good joint, without cracking the glass.

I've had luck doing the same with a Dremel rotary tool to carefully grind the glass away.

.

The Focus wire could probably be fixed with some conductive glue (rear defroster glue for instance) since it carries little current, the heater otoh will probably need a more direct connection.

So have I, as I described earlier. BUT PLEASE ... don't use it on a power tool.
Dangerous to your CRT!

Do it right ... go to store like Lowes or Menards and buy a nice, new
DIAMOND encrusted tool of suitable shape. I used a cutoff disk. And use
it BY HAND. Slow but safe.

However those wires look very close to being long enough as is.

If they stick up at all, they are long enough. Clean them with #0000
steel wool or fine sand paper. Tin them. Then solder on tinned #30 or so
wire ... I get it from #22 tinned stranded wire. Finally stabilize them
using sensor-safe silicone. Make sure they are long enough to go throush
the base pins.

With ordinary care, your tube will live just fine. Don't worry about breaking an extra wire ... I broke a filament wire on one of my 5BP4s fixing
a broken deflection plate pin, and it works fine.

I managed to tack on some wires with alligator clips on one end. Then I tested the CRT.

Viola! I didn't take any time to do any adjusting of the picture.

http://i1060.photobucket.com/albums/...psdoigf1ab.jpg

Thanks guys for the tips on fixing this CRT. Seeing it does test good with the wires hooked up I'll try and save this thing. Stay tuned.

:rockon:You may now claim the official title


SUPERTECH

:tresbon::banana::banana:

Well, the new wires are soldered on the CRT and sensor safe silicone has been added. Tomorrow I'll assemble the base to the bulb.

I used Dremel Cut-Off wheels by hand to start scratching the glass away. Then I switched to a #11 hobby blade and scraped the glass away. Then I used the hobby knife to scrape the wire clean and then tinned it.

I used some 30awg magnet wire and cleaned off the enamel. I then formed a very small coil of 2 turns. Yup, I'm using the coil method to attach the new wires to the stubs. A little flux and the wire was positioned on the stud and then soldered. A very nice shaped blob of solder told me I had it licked!

I then cleaned the joints with acetone to clean off the flux. A final rinse of alcohol and on went the sensor safe silicone.

http://i1060.photobucket.com/albums/...ps1d497ef4.jpg

http://i1060.photobucket.com/albums/...psizg7j7v4.jpg

http://i1060.photobucket.com/albums/...psev0pxq1p.jpg

http://i1060.photobucket.com/albums/...pskjslmyuw.jpg

http://i1060.photobucket.com/albums/...psilsowel0.jpg

Nice work. The coil method for the new wire is what I do too.

Thank you.

I put the base back on before I went to bed last night. I used the same sensor safe silicone. I then soldered the wires to the pins. Cleaned up the pins and we are ready to go.

I hooked the CRT back up to the TV and success!

http://i1060.photobucket.com/albums/...ps08kh7o4z.jpg

http://i1060.photobucket.com/albums/...psxrypfnts.jpg

I added a 10 ohm 25W resistor to the filament string. The filament string is for 115vac and my wall outlets provide 124vac. I thought that the 124vac would be a bit too much for the filament string, hence the resistor. The filament string is now at 117vac using my wall outlet. I used such a big resistor because I had one on hand and also I like to way oversize these things.

http://i1060.photobucket.com/albums/...psdgjwauu1.jpg

It looks like clearly defined scan lines now.
Are you running the chassis with the original B+ configuration, with just the 25DN6 upgrade?
Great job on the CRT lead wires. Those CRT's don't grow on trees! :thmbsp:

Glad you got the CRT focus sorted out and nice work! One thought - you might want to add a thermistor to give the tubes a soft start. Something like a CL-90 has a 120 ohms cold and around 3 ohms hot.

Not quite. Originally I had a 10 ohm 50W resistor (R69) in place of the 5 ohm 5W resistor that came with the kit. I used a 1N4007 instead of the selenium rectifier so I had to go up in resistance from the 5 ohms. Using my iso transformer and variac the 10 ohms gave me about 125 to 128V for the 130V bus (B+). Then I remembered that I'll be powering the TV using the wall outlets of 124vac. I had to go up to 15 ohms to get about 132V B+ voltage.

Thanks.

Thanks Bob!

Do you think I'll still need the thermistor even though the tubes have that 11 second delay built in?

Your line voltage is quite high! Ours is usually around 121 volts. The distribution transformer is on the lot next to me. A newer area, 15 years old. I imagine, the voltage is that high to avoid brown-outs in the summer time when everyone has their AC on. Your warm season is a lot longer than ours.
It's great to see that everything is working out fine. A lot of effort was put in and the results show it! :thmbsp:

With the TV plugged into the wall (124vac) I'm getting 135v B+ and 13.2 to 14.6Kv depending on the brightness setting.

This is with a 10 ohm resistor in the filament string and a 15 ohm resistor in the power line going to the rectifier.

124V is still within limits of ANSI C84.1.....127V max. I'm at 127V...

Not sure what you mean by that ? Is there some device providing a slow 11 second filament power up ?

According to the tube manuals, all the newer issue 600ma tubes have controlled heater warmup of 11 seconds. :scratch2:

On the 25DN6 tube data sheet they talk about controlled warm up period.

"Thermal characteristics of the heater have been controlled such that heater voltage surges during the warm-up cycle are minimized provided it is used with other types which are similarly controlled."

Then further down on the data sheet it states:

"Heather warm-up time. (Approx.)" 11 seconds

Most all of the tubes used have these statements in their data sheets.

Yes and typically tubes with an 'A' suffix like 6AU6A are designed for series string operation. It's still a good idea to add a thermistor for additional protection. They do a better job than the tube on it's own.

10-4. Thanks. I'll order some.

Here is what I used instead of the cork they supplied with the kit.

It is a very close cell foam that I get at Hobby Lobby. This is about 1/16 thick. I used some spray contact cement to glue them in place.

I also used the same stuff on the "inside" of the CRT strap so there isn't any metal to glass contact.

http://i1060.photobucket.com/albums/...psu7um9tym.jpg

http://i1060.photobucket.com/albums/...psqrjmdmco.jpg

I also made a "stand-off" from 1/16 phenolic sheet to help manage the HV lead from getting too close the the chassis and the lead from the fly-back to the HV rectifier.

http://i1060.photobucket.com/albums/...psuccjo3yu.jpg

There was a post either in this thread or on the other forum, suggesting that I might need some more filtering. Well I clipped in another 220uf cap parallel with C43B. There was no change to the B+ supply but the picture seemed a bit more stable. Hmm..... so I added another 220uf to C43A and again the B+ stayed the same abd the picture remained stable.

So if I add these E-caps to each C43A and C43B it will bring each up to 440uf. Does anybody see anything wrong with doing that? Would a lesser uf work?

I'm including a picture of that section of the schematic.

http://i1060.photobucket.com/albums/...psfdqtglun.jpg

I've been doing some investigating the focus problem I had with the help of another person offline.

Basically I cannot duplicate the focusing problem I had before I repaired the broken wires on the CRT.

If it was a broken wire I should be able to duplicate it by disconnecting pin 6 from B-. When I do, the picture remains in focus! NOTE - On the schematic, the blue wire from pin 6 shows it goes to chassis ground. This is an error on the drawing. It really goes to B-.


I've tried disconnecting wires on pin 2 and pin 10 with the same results, It still stays in focus. I even went back to the kit supplied 25CD6 and still stayed in focus.

I'm at a loss as to what caused the focus problem. I do know that after I fixed the the broken wires and reattached the base, the CRT stays in focus.

I'm including a section of the schematic so you can see what I'm talking about and maybe offer some reasons or suggestions.

http://i1060.photobucket.com/albums/...ps7xuavdhc.jpg

The extra caps will be fine. Back in the day would add extra filtering to get rid of audio and video hum. Have been following your journey with the build as I have a unit in my collection that was built 60 years ago. Not a real good job on the construction on the set I have. Thank you for posting the docs for construction of the set as my set had no info, so now I will start to fix mine. All the best,Tom.J

Tom, are you saying you have the same chassis? That would be terrific! What size CRT does it have?

Yes I do have a T-M 5516 and it has a 17 inch CRT. All the best,Tom.J