Couldn't have happened to something with 6146's - would have not been expensive enough ;-)
At least you found it. That's when stuff starts getting expensive. A lot of times, when an SB-220 would get a parasitic, that grid choke would get zorched. By the time that choke opened up, the grid was usually a goner and would short to the plate. I'd always have to sacrifice one 30 ohm resistor to test and make sure the tube was truly now just a lamp base and have to say that it was 100% of the time. Lots of controversy about AG6K and his suppressors. I've talked to the guy at length and he's not making a killing on those kits. He's very self-assured, but the stuff I've read tells me that he has reason to be. I saw loads of SB-220's with fried chokes, pitted tuning caps, fried relays and bandswitches and knew these were not all due to cockpit error. I even did a TL-922 with that kit once. You think the Heath parts were expensive... W1ES -----Original Message----- >From: Curt <cptc...@flash.net> >Sent: Dec 22, 2011 12:54 PM >To: drakelist@zerobeat.net >Subject: [Drakelist] Speaking of breaking Glass... > >I witnessed something recently that In nearly 50 years of working with >tube rigs, I had never seen. > >I was working on an older hybrid rig with 6JS6's in it. Had a known >good set of finals and was getting unit ready to ship to a new owner. > >Powered it on the bench and all was good..did a cold >neutralization...then reconnected filaments and powered up. > >Its sitting there at idle and I start hearing "tink..tink...tink..." >like tubes getting hot. I look into the final cage and see both tubes >filaments on. sits there some more..and I start smelling it HOT. Look >again and one tube is bright red plate. Just as I reach and cut the >power, I heard some arcing. > >Very strange I thought since it had all been working fine. > >So I open it all up and check out everything. 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> > >So, smart fellow that I am, I'm thinking bad tube right?. Just to be >sure, I double check the bias supply right at the sockets..looks ok. >All else seems fine. Double checked the driver plate coupling cap since >that can put b+ on the grids of the finals if it shorts..OK..it would >have smoked both tubes anyway. > >So..bad tube.. So I put back in a back-up set of finals..about 80% on >10M pair. Power on, quick set bias V , watch plate current, all >good........."tink tink tink..AWE CRAPP!...power off. Same tube >position is COOKING hot. What the.... > >So..smart fellow that I am, I plug in the bad tube and check the >resistance between the tube pin above the socket to the bias >bus...OPEN! Unbelievable...the grid pin connection in the tube socket >had been opened up to the point that it no longer contacted the pin on >the tube. Wide open throttle on one tube...even in standby....so no >indication on the multi-purpose, plate meter. > >Quick correction of the socket...a quick look at all the empty shelf >space where the expensive spare finals used to be stored...and the rig >is ready to ship.. > >Life is an expedition... > >Happy Holidays and controlled bias to all. > >Curt >KU8L > >_______________________________________________ >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
