Any advice on 40+ year old NOS glass power tubes?

[K8DI]

I’ve acquired a set of 4-400 tubes for my RCA rig, new/sealed, 1981 date on the boxes. These are European manufacture, they do not have the aluminum ring on the base. So, question one, does the ring matter? In the RCA there’s no spring clips or contacts to the aluminum bases, and those bases sit below the chassis (sockets are recessed).  Question two, best practices for successfully getting these tubes operational? Avoiding arcs, regettering, etc?

Ed

[w9jsw]

I built a hipot tester to initially check them out. Wired it in a triode connected manner. Had a known bad 3-500 that I put in the rig to see that the metering was working. It showed grid current almost immediately. Then ran thru 8 4-400s and they all passed not showing any grid current breakdown.  I then inserted them onto my drake L4B one at a time. It was wired for grounded grid. Made sure that each tube would generate RF. Measured grid current as a way to determine relative quality within the batch.

I think I am good to go now.

If I had to do this again, I would buy the hipot tester from Tom Raush rather than using the one I built. Safer.

https://www.ctrengineeringinc.com/hv-tester/

I made mine from an oil burner ignitor. It worked ok, but was sketchy.

[KA3EKH]

I would let the tubes cook at full filament for a while before applying high voltage. Almost every old broadcast transmitter I have worked with also applies bias when the filament is up so you will know if there are any issues there by looking at bias current during warm up. There should be none. Then maybe reduce drive and HV for first power up but beyond that not so much different from running a new tube. Don’t think there is any magic technique or “Tube Reforming” or anything beyond that. I use to run an RCA with 833 tubes and would often find old 833 at different transmitter sites I had been to that maybe have not been used in decades and never had any problems following that procedure. It’s a tube, its going to work or it won’t. Talking to it nice, slowly applying filament over a two-week period or whatever won’t change that.

[KD6VXI]

Running a filament style tube with just bias and filament does nothing.  They need the envelope to at least dull up to getter.

Install the tubes.  Bias them until they blush.

I've had 500Z tube's that would flash over at low voltage in an sb220.  I put 1kv on the plate and biased them until they glowed orange.  Left overnight.  They would now take low, but not high voltage. 

Kept the process up over a 4 or 5 day period, slowly increasing plate voltage and bias all the way to 4kv on the plate.  Tube's gettered just fine.

The really dangerous time is turning them on.  If any seals are bad, they will pop quick.

After that, slowly increase plate voltage and blush the nodes of the tubes to getter them.

--Shane
WP2ASS / ex KD6VXI

[W3SLK]

An elderly ham who is 'down-sizing' his station due to a move to a smaller house, is gifting me a 'transmitter tube tester.' He currently has it designed for testing 833's (for which he built an 80~15M amp!) and 3-500Z's. I'm going to expand its usage and hopefully be able to degas old tubes. I will have to find the paper work on how it is designed but maybe I'll start testing some of the old bottles in my possession.

[KA3EKH]

Degassing, flashing getters and glowing all night may be the trick! But I do not know. All I know is that when installing new power tubes and I have done a few in forty years of broadcast work the manufactures always say to run the tubes at filament for several minutes before applying power. Klystrons and IOT tubes in television transmitters had to be run at lower voltages and gradually brought up to operating temperature in the old analog TV transmitters or they would flash and throw crowbars, in AM and FM transmitters you would have to run an appropriate filament warm up cycle and after you can hit them with power and I have had pulls that sat on the shelf for ten or so years that just doing that they would come up without issue if they were good. If the tube is good it will work, if the seal is gone it will blow the filament in short order, if it works it works and if it’s a dud it won’t.
I am not disagreeing with your statement about running for several hours at high plate current and what effects that may have being I had no experience doing this but with respect let me ask a question, if vacuum has escaped from the tube how can it be put back? Or if the cathode is depleted from long hours of high emission how can that be rejuvenated?
Once again I am not trying to start a war or anything just asking for the logic behind your technique.

[KD1SH]

I'd never heard of that hipot tester. Unfortunately, the CTR website says it's not only out of stock, but implies that there wasn't enough demand to continue production, at least for now. Too bad; I might have considered it.
I've got a 10KV neon sign transformer, but I haven't gotten around to building myself a tester with it, though. When I do, I'll post some pictures.

I built a hipot tester to initially check them out. Wired it in a triode connected manner. Had a known bad 3-500 that I put in the rig to see that the metering was working. It showed grid current almost immediately. Then ran thru 8 4-400s and they all passed not showing any grid current breakdown.  I then inserted them onto my drake L4B one at a time. It was wired for grounded grid. Made sure that each tube would generate RF. Measured grid current as a way to determine relative quality within the batch.

I think I am good to go now.

If I had to do this again, I would buy the hipot tester from Tom Raush rather than using the one I built. Safer.

https://www.ctrengineeringinc.com/hv-tester/

I made mine from an oil burner ignitor. It worked ok, but was sketchy.

[K8DI]

Thanks for the advice, all. 

I would tend to agree that if the seals are bad, there's no getting the tube back.  On the other hand, forty years of metals outgassing or molecular level leakage might have put enough "dust" in the vacuum that it'll arc at full plate voltage, and activating the getter to get that dust out necessary.  After reading this and with other info I've found on getters in power tubes, I think a half hour of filaments to make sure the tube isn't full of air, then running a dull red plate for a couple  hourlong periods is in order. Being a broadcast box, half plate voltage is a switch flip to "night" mode; I'll put these in as modulators because the modulator bias is adjustable, then bring up the plate current as needed until they get good and hot. Then they can move over to the RF amp sockets...

With any luck at all, I'll be left with a set of fresh full-emission tubes and that will be the end of fighting with used up tubes in this rig for my foreseeable future...

Ed

[KA3EKH]

Cool beans Daddy O, at the end of the day what works for you is best. Don’t know about the RCA because my old BTA-1 used all 833 in the modulators and the several old Gates 1 kW that I use to take care of also used 833 bottles but I do know that a couple of the 1 kW Collins including maybe the last of that generations “Rock” transmitters all were rough on 4-400 being normal operation ran the tubes almost orange at full power and modulators would last about a year with the PA tubes maybe two. Life as a modulator in broadcast service was never easy, had a ITA 5 kW that ran four 4-1000 in the modulator and that would easily eat all four in less than a year with the pulls being all discolored by the time they were changed. Best thing about that was it provided lots of 4-1000 pulls that I would sell out at Hamvention every year for $20 each and back in the day that was good money! Around the turn of the century most stations went to solid state transmitters with all the old Gates/Harris stuff going into service as standby or removed and scraped. Still do a tube box every now and then, matter of fact I have a site that I have to go to this weekend and replace the tubes in a MW-5 that’s a backup for a DAX but most AM sites on the air for the last ten or twenty years are all running solid state Gates/Harris or BE transmitters and the day of the high-power AM Tube transmitter is over. The two bottles for the MW-5 came from a sister station and are Econco rebuilds, don’t think you can buy them new any longer. Forget what the PDM Modulator is but the PA tube is something like a 3CX5000

[KD6VXI]

Wait until ypu price an economy rebuild. For sat, a 3cx3000 today.

I about crapped myself.

Probably cheaper to buy a nautel than retube some of the bigger boxes.

--Shane
WP2ASS / ex KD6VXI

[KA3EKH]

I am not smart enough to be the money man, I just work for other people. So don’t get into paying for parts and then have to chase people down to get my money back. I just charge for labor.
Back in the day of the tube it was common practice to change tubes annually and I remember it was about $3,500 to retube a MW-5 for all new bottles, the Econco were half the price but lasted half as long.
Back in the eighties I did a maintenance contract for a real dump in Delaware, WJDY 1470 a 5 kW station. AM wasn’t dead in the eighties but it was dying. They had a CCA transmitter that needed all new tubes but had no money. So, they got some broadcast reseller to send them a set of bottles COD. Was told that they locked the doors and had everyone be quiet and not answer the door in hope that UPS would leave the new tubes on the doorstep but don’t think that worked out for them. Somehow, they did get the tubes and I changed them and assume they paid for them. This is the same station that called me once because their satellite dish stopped working because of an ice storm and for $250 a month, I was not coming out to knock the ice off. I told them to do it. The next time I was there saw that they dragged a three-drawer metal filing cabinet out under the dish, pulled out a drawer and set a fire in it to melt the ice. Good thing it was a metal dish and not fiberglass.
Sorry for stealing the topic and telling boring old broadcast stories but sometimes just can’t resist. Think I can tell several about WJDY alone.