I would not try to take the outer safety glass off, you could run the risk of an emplosion.<BR>Perhaps someone else on this forum could help you better than I.<BR>I have always left them alone and besides if I am not mistaken, that 15" color CRT you have is worth much more than any 21" color CRT.<BR>==========================<BR>Bill<P>------------------<BR>

I do hope you are wearing a bomb disposal suit when you are doing this??!!<P>Seriously, this sounds VERY dangerous to do on a tube under vacuum.<P>Eric<P>------------------<BR>

what 21 inchers have bonded glass on them anyway? My 56 RCA doesn't, it just has separate glass mounted in front of the tube.

I emailled the seller of the picture tube rebuilding plant presently on Ebay to ask for advice on removing and replacing the bonded faceplate. Here is the reply:<P>Hi Don,<BR>I will try to answer your questions.<BR>I never tried heating the face with a heat lamp but the concept is <BR>on the right path. I have replaced several of these faceplates <BR>over the years. I place the tube in the oven and heat it to 200 <BR>to 220 degrees C for 45 minutes. I then place a putty knife <BR>between the faceplate and the tube. It comes right off and while <BR>it is hot, just peel the old resin off of the faceplate and then <BR>clean off the tube. After the tube cools off, remove it from the <BR>oven and do the final clean up. I put the faceplate back on by <BR>using double stick (1/4 inch wide) around the perimeter of the <BR>faceplate. On some occasions, I will have to re-age the tube as <BR>it may drop off on the emission a little.<BR>Some tubes use a soft type resin that never totally cures. This is <BR>a bit gooey and sticky to work with. This type usually turns <BR>yellow around the edge of the tube. Some use a hard resin that <BR>totally cures. This type is much easier to clean up as it peels <BR>right off in large pieces. This type usually has white <BR>discoloration and sometimes little white and or black specks <BR>around the edge. The tubes and faceplates clean up quite well <BR>with lacquer thinner and steel wool.<BR>And as with any tube that is under vacuum, there is always a risk <BR>of cracking or implosion, especially if you don't take the <BR>necessary precautions. Never place a cold putty knife to hot <BR>glass or place the tube to any undue temperature changes.<BR>I hope this will help you with your project.<P>That all seems to make sense and I'd also be very cautious of implosion danger. I've asked what double stick is (perhaps common knowledge in the US?) and will post an answer if I get it. I also suggested the buyer of the equipment post on the resources section of the forum if there's a commercial rebuilding service.<BR>I have an RCA round tube 21" set that has a bonded tube, it would be late fifties / early sixties vintage. I also have 21" tube that doesn't have any protection.<BR>I hope this helps.<BR> Don Black.<P>------------------<BR>

Here's a follow up on replacing the faceplate.<P>Hi Don,<BR>I guess it was getting late last night. I'm sorry I left an <BR>important word out of the information. The double stick should <BR>have read...double stick tape or also known as double sided tape. <BR>The measurement of the tape is 1/4 inch by 1/8 inch thick and it <BR>is foam rubber. I used to use the resin in the tubes but it was <BR>getting too costly and time consuming. You had to purchase the <BR>resin in a minimum amount of 5 gallons and you also needed the <BR>catalyst and then there was also the shipping. You had a time <BR>frame within to work with the resin once it was mixed with the <BR>catalyst. You had to pour it into the cavity between the <BR>faceplate and the tube. Sometimes I would end up with a bubble <BR>or sometimes it would start to cure before it was all in. It was <BR>very messy, costly, and time consuming.<BR>I hope this cleared up some of the confusion.<P>Don Black.<P>------------------<BR>

hello<P>Not to advertise, but the only company that comes to mind for things like specialty tapes and the like is the US company 3M. So I just checked out their web sit.<BR> <A HREF="http://www.3m.com" TARGET=_blank>www.3m.com</A> <P>There are a lot of products, available world wide. I didn't bother to see if they sold direct, I was only thinking availability, and double sided foam tape for electronitcs is.<BR> <A HREF="http://products.mmm.com/us/electronics_mfg/products/electronics_mfg.jhtml?powurl=GSMNRGC5GVbeGSFVD9HJ6SgeGST1T4S9TCgvGSBY2MCRKZgl" TARGET=_blank>http://products.mmm.com/us/electronics_mfg/products/electronics_mfg.jhtml?powurl=GSMNRGC5GVbeGSFVD9HJ6SgeGST1T4S9TCgvGSBY2MCRKZgl</A> <P>I hope that address is right, the site is easy enough to navagate if its not and my appologies, I'm new at this internet thing, and I've only used that copy function twice now.<P>Todd<BR><P>------------------<BR>

Hello<P>I think what the issue is is that glass and metal both contain a fair amount of gasses includeing oxygen. By heating the glass beyond the normal operatin temperature you've re-released this into the atmosphere(vaccume) of the crt. This likly would cause an oxidation of the components of the gun. Aging the tube would re-rarify the oxygen to be re-absorbed by the getter.<P>Of couse this is merely scratching my head thinking, there may be other issues at work as well.<P>As to how to age a tube, the only instructions I have are for a 12AU7, but I believe that the ideas much the same.<P>"Befor installing a 12AU7, age the tube by connecting the grids and cathodes to one side of a 117 volt, 60 cycle line and the two plates to the other side of the line. The heaters should be operated at normal voltage. The tube should be operated in this manner for a minimum of 12 hours befor it it installed in the instrument. The calibration should then be checked."<P>That paragraph was copied from an RCA Seior voltOhmyst type wv-97A manual. I'm going to have to invest in a page scanner, would have so much easyer than typing!<P>Todd<P><BR><P>------------------<BR>

Here's the reply about aging the tube:<P>Don,<BR>Probably a quick re-age process would get you by. Although this is only required when the tube is heated to the temperatures I previously described.<BR>This quick ageging schedule should work on most tubes.<BR>6.3 volts for 5 minutes<BR>11 volt for 2 minutes<BR>Hope this helps.<P> Don Black.<P>------------------<BR>