Have never experienced this and hope I never do. These sweep tubes are getting too precious.
3-500's have much thicker glass than even 811A's, so I don't think it would be very easy to get a suck-out on one of those puppies. I have seen the grid get shorted to the plate - usually as a result of an initial parasitic oscillation in the tube. I've repaired lots of SB-220's and the problem is fairly common in them. I've never heard of an L-4 or L-4B failing like this... Steve, W1ES/4 -----Original Message----- >From: Richard Knoppow <1oldle...@ix.netcom.com> >Sent: Dec 22, 2011 1:26 PM >To: Eddy Swynar <deswy...@xplornet.ca>, Curt <cptc...@flash.net> >Cc: drakelist@zerobeat.net >Subject: Re: [Drakelist] Speaking of breaking Glass... > > >----- Original Message ----- >From: "Eddy Swynar" <deswy...@xplornet.ca> >To: "Curt" <cptc...@flash.net> >Cc: <drakelist@zerobeat.net> >Sent: Thursday, December 22, 2011 10:08 AM >Subject: Re: [Drakelist] Speaking of breaking Glass... > > > >On 2011-12-22, at 12:54 PM, Curt wrote: > >> All looks ok EXCEPT..the one tube that was bright has a >> small suck-hole thru the side of it. It got so hot, the >> glass melted and a hole was sucked thru the side without >> breaking the rest of the tube. YIKES> > >Hi Curt, > >That happened to me one time here, too, only the >circumstances were a bit different... > >I had a brand new pair of 811A tubes in my 500-watt >amplifier, & had just purchased a Yaesu FT-980. I got so >enamoured with my being able to "...raise the average talk >power" of my SSB signal by virtue of the new rig's speech >processor that after about 5, or so, DX QSOs on 20-meters, >the fuse in the amp's power supply popped. I replaced it >with a new one, and again, it blew... > >So I took off the amplifier's covert & examined the new >tubes...and lo & behold, there was a tiny pin hole in the >envelope of one. I guess my speech processor raised the >plate dissipation of those jugs as well as my "...average >talk power", to the point that the one tube got so hot the >glass had softened, & the vacuum was sucked out! > >I've never used a speech processor since that time. > >~73~ de Eddy VE3CUI - VE3XZ > Eimac featured this effect when they began selling >ceramic tubes. They showed a picture of a glass tube with a >suck-hole in the side and a ceramic operated under the same >conditions that did not. I think they said the suck hole was >the result of electron bombardment of the tube at high >frequencies but its possible that any inclusion or weak spot >in the glass could do it. I've had tubes crack from >overheating but have never had a suck-out. > > > > >-- >Richard Knoppow >Los Angeles >WB6KBL >dickb...@ix.netcom.com > > >_______________________________________________ >Drakelist mailing list >Drakelist@zerobeat.net >http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
