Hi All,<BR>I was given a Motorola 12T3 (chassis TS-53)<BR>about 10 years ago. I remember plugging it in when I first received it and set was dead.<BR>I am experienced at TV repair, but have never worked on a TV this old. <BR>I was wondering if there is anything in particular that I need to look out for in a set this old. I would like to do the minimum to get the set running just incase I need something major like a CRT.<P>Thank you for any advice offered.<P>Scott <BR>Polaraligned@aol.com<P>------------------<BR>

Scott:<P>I install a 2 amp fuse, replace the filter caps and paper caps in the Horiz osc. section before powering up with a variac. You may have an open fusible resistor if the set is dead. I do not have a schematic handy for your set. <P>One side of the power line may be tied to the chassis so use an isolation transformer if you have one. If you don't, be careful. <P>Replace all of the paper and plastic coated paper caps after you determine condition of CRT, HV, etc. They are either bad or will be bad. Standard troubleshooting techniques apply. Use your eyes, ears and nose.<P>Other members may have other ideas and procedures. <P>Good luck.<P>Tim<P>------------------<BR>

Even if the CRT is bad, they are not too hard to find. <P>------------------<BR>

I agree with Dr. McVoy here; it is a myth in my opinion that a bad CRT renders a set a "doorstop". It's not like you trip over them, or Radio Shack has them, but they can be had. Few other people want them, really. One appeal of TV collecting, after all, is the technical and parts supply challenge. It's half the fun, and half the learning. Anybody can snap in a new vertical output circuit board, after all.....<P>------------------<BR>

I remember when I worked in the business<BR>back in the early 80's, (I was in high school and part time), that the owner of the<BR>shop would send the CRT out to be rebuilt.<BR>It was my impression that the gun was replaced in the tube, but I could be wrong.<BR>Is there anyone out there that still "rebuilds" picture tubes??<BR>Could be valueable to collectors.<BR>Think the owner is still around. Maybe I will<BR>contact him and question him on this.<BR>It's hard to imagine that people have kept NOS picutre tubes all these years. Any electron tube (except sweep tubes), that are a TV specific tube is not worth the space they take up and are discarded by the thousands every day.<P><P>------------------<BR>

There are at least three companies that still rebuild tubes. However, it is very expensive ($250 and up). There are still lots of good tubes out there - many times the sets were junked, but the CRT kept around. 10BP4s and 12LP4s used in almost all 1947-1950 sets are easy to find. 7JP4s used in the 7 inch sets of the late 40s are harder to find, but often you can find a junk set at a swap meet for under $50 with a good tube.<P>Later tubes are also fairly easy to find, except for the 15GP22 and 21AXP22 color tubes.<P>------------------<BR>

Steve,<BR> Where can I find a good 3KP4 CRT?<BR>Is there anyone that rebuilds them without paying $250? Mine has low emission.<BR>Thanks in advance.<BR>Bill<P>------------------<BR>

They are hard to find. Have you tried boosting the filament voltage? If you are only using the set periodically, the tube will still last a long time at even 9 v on the filament. The current of the 3KP4 is the same as 10 and 12 inch tubes, so if you can find a series model picture tube booster (they come up on Ebay frequently), you can install it under the chassis.<P>------------------<BR>

Steve,<BR>Thank you for the info.<BR>I think my tube may be gassy because the picture goes negative when the brightness and contrast is brought up, and the set has to be viewed in a dark room.<BR>I borrowed another 3KP4 from a friend, and put it in my pilot, the picture was great and did not go negative.<BR>I also put a 6.3 volt filament transformer for the CRT in the set and installed a resistor to drop the filament voltage on the string.<BR>The surge can kill the CRT as you know.<BR>Thanks again, Steve.<P>Bill<P><P>------------------<BR>

I'll try to keep this simple. <BR>Back in the mid-fifties in the golden days of pre-color, A close friend worked for a CRT rebuilder across the river in Windsor, Ontario. I often went there at night to gab with him. He had the whole operation to keep going all night. I'll skip the process, and deal only with the final operation. The new gun will not emit electrons, after evacuation, and final processing. There is contamination on the cathode coating that blocks emission and must be stripped off. They took a 3.5 watt night light bulb, in series with +100V. DC, and connected it to the control grid, with negative to the cathode. They applied the normal 6 volts to the heater, then stepped it up to possibly 10 volts, over a period of a couple of minutes as I recall. During this, the bulb began to glow, and came up to brightness. Filament voltage was then cut back, and the bulb was quickly disconnected. The tube was now operational. The tube "rejuvenators" do this process in a fraction of a second, and the results are questionable. I am planning on doing this to the CRT on one of many of the little RCA 8 inch sets from the late fifties. They're always weak. I have enough of them that I can afford to experiment. Anyway, with use, the cathodes become contaminated, and need a "cleaning off" like that. <P>------------------<BR>

Doug,<BR>Keep us posted on the results of your<BR>"cathode cleaning" experiments. If this process works well it could prove very useful to many folks who have low emissions.<P><BR>------------------<BR><p>[This message has been edited by Polaraligned@aol.com (edited 12-05-2000).]