<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px"><div><span>I still have my original Cetron tubes in my SB200.</span></div><div><span>I built it when the SB200 first come out in the 60's...</span></div><div><span><br></span></div><div><span>Never abused and never ran high grid current, only</span></div><div dir="ltr"><span>enough to make the power i wanted.</span></div><div dir="ltr"><span><br></span></div><div dir="ltr"><span>Still going strong.. 8-)</span></div><div dir="ltr"><span><br></span></div><div dir="ltr"><span>Jerry</span></div><div dir="ltr"><span>W3CDE</span></div> <br><div class="qtdSeparateBR"><br><br></div><div class="yahoo_quoted" style="display: block;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"> <font size="2" face="Arial"> On Tuesday, August 11, 2015 11:46 AM, Kenneth G. Gordon <kgordon2006@frontier.com> wrote:<br> </font> </div> <blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; margin-top: 5px; padding-left: 5px;"> <br><br> <div class="y_msg_container">On 10 Aug 2015 at 21:56, Wilson Lamb wrote:<br><br>> I'm very aware that I have a limited view on this and am happy to learn. <br>> So if there are sites that explain what is going on and can verify that the<br>> treatment helps, they would be most helpful and interesting. And how do we know<br>> a failed tube would have been helped by gettering??<br><br>My understanding and experience tells me that gettering will NOT help a <br>completely failed tube: that process is really only useful for a good tube which <br>has not been used for a long time.<br><br>Tubes with plates made of the same material as the 572B (carbon?) getter <br>continually while being used. When such a tube has not been used in a long <br>time, usually a couple of years at least, they sometimes must be "gettered" <br>before use in order to prevent arc-overs when HV is applied due to the <br>residual gas that has built up in them.<br><br>I am ambivalent about re-gettering unused tubes: in my experience <br>sometimes it helps, and sometimes it does not appear to do any good <br>whatever. In my opinion, since the PLATE is what does the gettering, the <br>proper procedure would be to apply some plate voltage to the tubes as they <br>are "cooking", but not enough plate voltage to arc over. I.e., connect them as <br>a diode.<br><br>It is sometimes possible to "reactivate" thoriated tungsten filamented tubes <br>which have gone "soft" or in which the filament-emission has fallen by <br>depeltion of the thorium layer, by operating them with filament voltage only for <br>a while.<br><br>That filament voltage, however, must be noticably higher than the NORMAL <br>filament voltage in order for any residual, unavailable thorium to be "boiled" to <br>the surface of the filament.<br><br>That thorium layer, by the way, is only one molecule "deep".<br><br>For instance, in an old handbook I had at one time, the suggested procedure <br>for reactivating thoriated-tungsten filamented transmitting tubes was to apply <br>2.5 times the normal filament voltage to the tube (with no other voltages <br>applied) for 1 minute, then reduce that voltage to 1.5 times the normal voltage <br>and hold it for 1 hour, then test the tube. If the tube had not regained its <br>normal plate current capability by this procedure, one repeats the procedure, <br>then re-tests. If the tube is not back up to normal by then, then discard it.<br><br>Using this procedure, I successfully reactivated about a dozen 304TLs I was <br>given which had been used as shunt regulators in an NMR machine. These <br>were so flat that they wouldn't draw even 10 mA with 2500 VDC on the plate <br>and NO grid bias.<br><br>After reactivation, they performed as new in amateur service for many years <br>afterwards.<br><br>HOWEVER, when I tried this same procedure with flat 572Bs, it was only <br>marginally successful and the effect didn't last long.<br><br>I then asked a manufacturer of tubes about this process, and it was <br>suggested to me that raising the filament voltage of 572Bs to only 1.5 times <br>the normal filament voltage for 1 minute would probably help redistribute the <br>thorium, at least for a while.<br><br>Also, FYI, I spent quite a bit of money and at least two years of part-time <br>investigation to learn all of the above while trying to figure out how to get <br>572Bs which would work longer than a few months in my own SB-200s.<br><br>The only solution which worked was to buy those new 572Bs which RF Parts <br>is now selling after THEY did over a years worth of work to find a maker who <br>would make them at least as well-made as the old Cetrons.<br><br>As far as I am concerned, RF Parts succeeded admirably. I have a pair now, <br>and they are really superb, and the cost is much lower than I had anticipated.<br><br>I intend to buy another pair as soon as I can get in the queue.<br><br>YMMV.<br><br>Ken W7EKB<br>_______________________________________________<br>Heath mailing list<br><a ymailto="mailto:Heath@puck.nether.net" href="mailto:Heath@puck.nether.net">Heath@puck.nether.net</a><br><a href="https://puck.nether.net/mailman/listinfo/heath" target="_blank">https://puck.nether.net/mailman/listinfo/heath</a><br><br></div> </blockquote> </div> </div> </div></div></body></html>