The AM Forum

I lost a filament in one of the 100ths in my PP 20M AM rig...going thru the junk box tubes and this one turned up....Out of 6 tubes, this is the only one that will give me any color..They are all targets...

Hey Steve,

Were any of those 100TH's I sent you good tubes? Or were they all duds too? I think I have a couple more if'n you need 'em.

Ron

Hi Ron...Yeah, all duds.....This gassy one was in the box you sent...I could use a couple good ones... Steve

OK Steve,

Four more 100TH's coming your way. Hopefully one of them is good, 'cause these be my last ones!

Ron

Lookz like one of them there special applicatiom mercury vapor 100THs  ;D  ;D

Don't "target" them all..... I'd be interested in one for display....
thanks
Carl
/KPD

Is the day of the 100 TH and 250 TH thru? Are those tubes so old now that they are expected to have leaks and loss of vacuum? I never owned a BC-610 transmitter yet but have to wonder if  the tubes are all dead or dying what's that say about the future of BC-610? I have had a couple old navy transmitters using 803 tubes but the tubes I had all were strong and had no issues despite their age, ART-13 transmitters and 813, 811 and the like all appear to be strong and available and my RCA with three 833 tubes appears to be almost indestructible, at least in ham service, but if the "fish bowl" tubes are done then maybe I should cross the BC-610 off the want list. 

A pair of 572-Bs for modders, and an 833 for the final, and play with the biass voltages, the BC-610 will still live on for many years to come ;)

Carl...email your address and I'll send you a display tube...Steve

There is still a lot of 100TH's out there and for that mater 250TH's as well. The thing to do is stay away from anything other than Eimac. Possible exception would be tubes by I.C.E. Most other types are gas bombs.

I'm using a pair of 75 year old 100T's in my 610 right now. The strange thing about these tubes is they can be just fine for years and then one day, a seal gives and you got a glower!!

I think it's more a case of contamination through inferior metals for many of them, Ray. During WWII when these tubes were in heavy use, metals were also in demand for the war effort. The result was a reduction in purity for the metals used in many of these tubes. The impurities leech out over time, contaminating the vacuum. At least, that's how it was explained to me by an OT who was involved back then. I don't recall any mention of vacuum/seal issues, but it's always possible.

The trick would be finding post-war tubes to have on hand in the event that a tube in use ends up being gassy. IIRC, they were still being produced in the 50s or 60s from date codes I've seen. There are also pre-war tubes still working fine today.

When I first saw this thread title, I wondered "what happened to the first 99 gasses?" ::)

Anyways.... ;)

I have lots of vintage transmitting tubes here, and when testing to see what to keep or not, the ones with the uranium salt seal (identified by the greenish area around the stems) hold up the best.

Good or bad, it runs across all the brands, more by type than maker.

73DG

When I first built my 100th rig, the only tubes I had were a little gassy...They worked but had a light blue glow inside..after letting them cook on the filaments for 24 hrs, I began to use them.....with use, the blue slowly disappeared until all that showed was some little blue donut shapes that would walk up and down the plate stem when the high voltage was on...eventually those too disappeared and I would guess I got a hundred or so transmitting hours out of those tubes...

Make that triode connected 813s for mudulators.

Drive the 813s with an old junk stereo set and hi-fi output xfmr backwards. Sell the 2A3s to a collector : )

833 final works FB with very few mods. Even a 3-500Z works in there.

If peer pressure disallows JSment use 810s for mudulators.