On early sets (earlier than something like 1970 or perhaps 1965) the measurement was on the diagonal from the outside edges of the glass. Later sets are measured on the diagonal but measure the screen where there is phosphor. This leads to picture tube numbers that differ by as much as 2 inches that are actually the same size.

That sounds more like a 17-inch tube. This website has tube data sheets with dimensions and other specs:

http://tubedata.tigahost.com/tubedata/

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Today I replaced all but one of the electrolytics. I had missed one when I ordered the new ones. Oh well, it's not like I can power it up since I runied the CRT. I'm leaning towards thinking it's a 16" CRT. I measured a 17HP4 today, diagonally which masured 17". This one measures 16" diagonally. Ofm course, there's a good chance I'm wrong too.
Phil, thanks for that tube website, but what exactly am I looking for on it? Do I need to take each one of the 16" CRTs the Sams list as well as the two 17" ones and try to download a datasheet.

The two 17" replacements are 17AP4 and 17BP4. The Sams list a not saying space permitting. I'm sure both the 16" & 17" will fit the chasis. Perhaps I need to measure the cabinet as well as the front tube mask to see what will fit.

Doug

The data sheets give exact dimensions for the various tubes. Comparing the size of your tube to the dimensions in a data sheet should tell you what size tube you have. You're the only on who can measure your tube.

You don't have to download a data sheet unless you want to. Just look it up by type number, click, and view the sheet.

Phil Nelson

Phil, I finally figured it out. I typed in one of the 17" numbers and got the dimensions and then typed in one of the 16" numbers and did the same. I do have a 16" tube. The measurements are exact on my tube according to the data sheet for a 16KP4 which is one of the 16" CRTs.

Thanks for steering me to that sheet.

I now need to locate a 16KP4, 16RP4, 16XP4, 16TP4 or 16GP4. According to a tube substiution book I looked at all ate interchangeable. If anyone has a good one to sell, please PM me.

Thanks
Doug

Never mind I was responding to the last page not knowing that this page was here and had already said what I was going to.

This project is currently on hold while I locate a CRT. I do have one question. If I get an 8YP4 test CRT, could I sub that for my 16KP4 so I could power up the set and continue restoring the chasis?

Doug

8YP4 has the wrong pinout to sub for 16KP4:

http://tubedata.tigahost.com/tubedata/s ... /16KP4.pdf
http://tubedata.tigahost.com/tubedata/s ... 8/8YP4.pdf

I used an 8XP4 to sub for the 17AP4 in my DuMont RA-113:

http://tubedata.tigahost.com/tubedata/s ... 8/8XP4.pdf

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

You would be better off using 5AXP4 test tube. The 8XP4 deflection angle may result in serious neck shadow. That won't affect any debugging.

As for your doorknob cap, try gutting it and hiding the new disc inside it. Or, gut the doorknob, epoxy it back together and install the new cap outside it. One thing you want to check is the 1B3 socket. Mine had a burn trail inside it. I replaced it with a plastic one.

Thanks for the advice guys. Now I'll know that to look for in a test CRT.

Doug

I should be ready to get back into this project by this weekend. I have not had much success in locating a 16KP4 replacement CRT. What I mainly want right now is some type of test CRT that will allow me to do an initial power up of the set just to see what I have. I knocked the cap off the old CRT while I was recapping the chasis and never was able to do an initial power up. I thought I could resolder the leads bac where the broke off the old CRT, but upon checking with my meter, I have no filament anymore, so the CRT wil not be usable.

I did some research on the Tube data charts that Phil provided me with and was wondering if a 10BP4 could be subbed for a test CRT. The only difference seems to be the max anode voltage for a 16KP4 is 16,000V vs maz of 10,000 for a 10BP4.

The only other tube I have is a 17TP4, and while the voltages are the same, I see it has 4 grids vs 3 on the 16KP4.

Doug

Ok, I'm going to ask a dumb question. I'm ready to set started back on this set tonight. My CRT is beyond repair since I knocked the cap off. I checked it's filament and there was nothing. It's a parallel circut. If I connect the HV anode to the bad tube, could I then atempt a power up with my variac? Of course I won'd have any pic, but I copuld at least see if I have any audio after recapping it or at least see if its gonna smoke.

Doug

Either connect it to the bad CRT or position it so that it is several inches away from anything.

About the CRT filament, the wires where they exit the glass are often covered with some corrosion. If not already done, it might be worthwhile to scrape the wires clean and recheck the filament with your ohmmeter. The corrosion could have prevented you from getting a good connection to your ohmmeter's test leads.

Tom, I tried scrapping the wires with a kinfe the other night, but I'll try again. I may not get around to trying a power up tonight anyway. When I knocked the cap off the CRT, I had all but one electrolytic replaed (and it was on order). Disgusted I put the set aside and moved on to the Admiral with the horiz issues. So I'm got to study my Sams tonigjht and figure out which filter still need replacing and try to remember what I had done and what I needed to do. I should have wrote it down as I was working on it

Doug

Update: I figured out what I had done and what I needed to do as far as finnishing the filters. They are all installed, and I remembered the HV doorknob cap was broken. I had ordered a replacement for it and just installed it. I set the old CRT face down on the dining room table and connected the anode. I hooked up the Variac and SLOWY started increasing voltage. Right now the tube filaments are measuring 2.5V, and the B+ reads about 10V. I'm going to let it cook for awhile like that then slowly increase it.

Doug

Note that if the coating on the outside of the CRT is not grounded then it will pick up quite a high voltage because of capacitive coupling the the internal coating. I sometimes use a small (12 inch or so) glass CRT as a test CRT. When I do that I tape a wire to the outside coating and connect the other end to the chassis.

Tom, I think I've come up with a good solution for the grounding. There is a spring type wire that is on the top of the metal yoke housing to ground the CRT. I have simply pushed the CRT up agaunst this wire as shown in the pic. Thanks for letting me know I needed to ground it.

While bringing it up slowly, I had walked away for a few min and heard a loud pop. I rushed back in to find one my of new electrolytics smoking. Upon inspection, I had installed it backwards. Luckily, I didn't ruin it. It was C1A that does the 410V line.

I started another power up, and this time got some decent B+. I have the 410V line up to about 300V and the tube filmaents were reading 3.9V when the horiz centering control started arching. It's a 30 ohm wirewound control with C3 across one end and middle lug. C3 is an 80mfd. I guess I need to try to replace this control next. Will a reg 30 ohm potentiometer work, or does it have to be wirewound?

Doug

I ordered a new wirewound control last night, but in the mean time I decided to try a reg 25 ohm potentiometer. I installed it, then I did something stupid. I plugged in my Variac, and instead of plugging the TV into the Variac, I plugged the TV into straight 110. Oh well, I got a full power up with no smoke. After about 30 sec, I heard that hi pitched whistle you hear in and old B/W TV, but that all. No audio. I looked at the Sams which shows a 6V6 as audio output. Checking voltages revealed no plate voltages on pin 3, but plenty of voltage on pin 4. Between pins 3 & 4 is a .0068 which I had missed. I snipped it out, and found it was a .005. The closest I had was a .0047, so I installed that with no results. I then turned to the audio output transformer and got reading on the primary with my ohmmeter. I'm gonna look in my junk box tonight and find another one then go from there.
Doug

I installed another audio transformer and fired it up. Now I can hear static as the channels are being changed or as the dirty vol control is rotated, but I never could hear any audio when the cable was hooked up. Without a CRT, I'm stumbling around in the dark. I got out my signal injector and traced back from the spkr to the vol control, and audio passed thru. Checking voltages on the 6V6 audio and 6SN7 AF amp were fine. I decided to quit and run all the tubes thru the checker which I had never done. I started on the tuner. The converter is supposed to be a 6J6. In it's place I found a 12AT7. I wonder if that's my problem. Right now I'm trying to see if I have a spare 6J6 lying around.

Doug

Hmm... A 6J6 is a 7 pin tube and a 12AT7 is a 9 pin tube. Perhaps there was some sort of production change and you have a different tuner.