The AM Forum

Transmitting Tubes

That SB-220 need a new set or just spares ?

Nope. Not yet. Spares go bad if you don't rotate them.

I don't think so.  I have seen tubes of that type that sat in boxes for over 10 years then installed without issue.  

I have found it all depends on how well they were made.  Some NOS tubes (big ones, too) I have are over 80 years old now, still as hard a vacuum as you could want.

Once I test them here, they go on the shelf waiting for a project.

I've got some new jobs and found them gassy out of the box.

Buying tubes is a crapshoot, just try to keep it off yourself ;).

73DG

I agree. I've owned several that were wrapped in newspaper with Watergate headlines.

They fired up just fine.

I believe the issue is hamateurs who didn't understand they need to run orange once in a while along with some bad batches.

Most of the problem with glass tubes is some people do not know how to insert or remove them.  They rock them back and forth to remove them from the socket or do the same to insert the tube.  That causes stress where the pin exits the glass which causes minor cracks that expand as the tube is heated and cools.

That is part of the reason manufacturers put ceramic bases on some of them like the 4-250, 4-400 and up.  That made them a lot more sturdy for people who did not understand what they are doing.

Unless there is a bad run, gas in tubes almost does not exist and if you follow the manufacturer's installation directions you will not have a problem.  

A guy in my neighborhood sells a lot of pre-owned ham gear.

There was this guy who purchased an L4B from him and removed the tubes. For some reason he decided to test the tubes by shaking them violently.

We found this out when we all met at guy#1's house to test the tubes that had been removed.

Tube shaker guy writes a lot of stuff appearing on ham websites.

Oooooooouch.

Jim said:

"Most of the problem with glass tubes is some people do not know how to insert or remove them.  They rock them back and forth to remove them from the socket or do the same to insert the tube.  That causes stress where the pin exits the glass which causes minor cracks that expand as the tube is heated and cools."


Interesting.

What is the best way to remove a tube that is "stuck" or not coming out easily when pulled straight up?  

Does this apply to both smaller tubes and larger transmitting tubes?

The leverage is greatly increased by rocking and non-existent when pulled straight up, so I can see why rocking the tube becomes a natural, though stressful, way to do it.

T

If a tube has seized in the socket, it may need to be rocked gently to free the pins, but after they are free, I pull straight up to remove the tube.  Most problems occur when the pins are sufficiently above the socket where leverage can be exerted on the base junction.

I have also seen problems with tubes that have the plate pins exiting the bulb on top.  If one is not careful they fracture easily especially the 829 and 5894 types that have thin envelopes.  Small receiving tubes rarely are subjected to operational conditions that cause the pins to seize and the miniature types have pins that are a lot more flexible so rocking has never been an issue for me.  It is just those darn expensive transmitting tubes that I worry about especially now that prices are astronomical.

Yes, very expensive, like a new 4-1000A costs $2,000 at Richardson these days...  :o


What sometimes scares me about pulling a tube straight up is the grip we need around the glass body. I sometimes wonder what would happen to my hand if the glass collapsed.  But in reality, I'll bet even with leather gloves I don't have the strength to crush a 4X1.  

The 4X1 has a strong ceramic base, but I plan to be more careful in the future when pulling them out. I tended to rock them gently. Overall, it seemed like the least stress was to rock, but I can see it was not.    It also depends upon the mechanical structure of the socket pins. Some of the new Chinese sockets have little give and are a bigger risk - while the older Eimac seem very springy in comparison.


Yes, top tube plate caps can be fragile. I've had one or two 811A/6146 type-tubes lose their glue and fall off, even though the pin and seal was OK. I epoxied them back and all FB.    The main thang is to use a very flexible plate lead that puts no mechanical stress on the tube cap. I am very anal about this and always use a flexible buffer between the cap and any copper strap to the plate.

T

I always try to grab a tube as low on the envelope as possible to help with the breaking problem you fear, and for good reason.  I also use leather gloves or a doubled towel.  That ceramic base was added to prohibit some of the problems of micro cracks and helps immensely.  But even with the ceramic base, considering the cost of high power tubes, I try to be as careful as possible as you so aptly state.

In short, the less stress and shaking that happens upon insertion or removal of the tube is much better for it.  But, as to the original comment, I have never had a high power tube fail to operate correctly due to gas in the envelope.  People who are neophytes about high power tubes should read about the procedure to start them in service by the manufacturer rather than unwashed comments.  They are different for tubes with different types of filaments and anodes.

I doubt seriously anyone with a lot of experience were unaware of potential problems but I have seen all types.

I invented a puller for big tubes like the 3-500 and 4-1000. I could not get it patented. Probably a moot point now. Just a strap of fiber reinforced, low dielectric K, 0.010 thin, strong, plastic-like material composite having some holes in the right places for air that was laid down and then the tube plugged in. To remove, attach the long 'ends' (straps) to the installed piece and pull straight up, using the other hand to steady the tube so it doesn't pop up from the socket and bust. It was designed for HF, maybe 6M. At the higher VHF range its small dielectric constant might affect grid tuning slightly (not tested). The socket cylinders on the 4-1000 air system socket are free to move a little. It makes it less stressful on the tube IMO.

Always use proper leather gloves and safety glasses when removing these large tubes.  It is very rare for one to fail but the implosion is impressive and rocking one can pop a seal causing instant destructive failure rather than the more typical slow leak.  It may sound like overkill but safety equipment is like insurance, by the time you owned it the time is too late.  There was an article in one of the 1950s service magazines about a tech who did a near complete amputation of his thumb trying to pull a stuck 7F8 (loctal) tube out when it shattered.  If a little loctal can do that imagine what a 4-400 or 4-1000 would do.

If a large tube is really stuck do the smart thing and use one of the penetrating agents on the pin/socket interface (but no overspray) and let it sit awhile.  The extra time spent doing this could easily save a very expensive tube.  Later 3-500Z production from most manufacturers added an additional base support (like the photo show by the original poster) which both reduces the stress on the pins and provides some elevation so the simple fan cooling system like that used in the SB-220 and Drake L-7 can better cool the base seals.  The earlier 3- series is very easily damaged by rocking.

Fresh DOT-3 automotive brake fluid applied with a Q-tip works great for dissimilar metals binding. Use sparingly and keep away from paint.

Replacing them in a BC station doesn't always allow time for chemicals to work.  Every minute of silence costs money and the same for the old IMTS base stations.  With ham radio you can get away with delays, but commercial service has a different set of demands.

That broadcast stuff sounds like serious business Jim.

Silence is not acceptable in the BC industry nor when all you  have to sell is airtime.

Safety can't be over emphasized. People think the danger is turned off with the high voltage. When I was a kid, I used to recover monochrome CRT phosphor. In those days, old TVs and large parts were often piled up behind the shops in the rural areas until a truckload was accumulated for the dump. The tubes had to be broken in several stages to leave mostly the faceplate but there was left still a sharp edge all the way around the faceplate; the root of the bell. After 40 years there is still a mark on my palm from a deep cut that should have been stitched. I was more concerned with not being found out for a foolish activity by my father than with enduring the stitches.

Looks like this one failed to survive the "shake test"   :) 

http://www.ebay.com/itm/Eimac-4-400A-Electron-Power-Amplifier-Tube-/221398494319?pt=Vintage_Electronics_R2&hash=item338c60ec6f

The seller is selling the plate cap in another auction. He may list the vacuum in a third auction next week.

Maybe he'll sell code tapes in another auction.

That explains why he states in the auction for the tube, "Sold As is, No way to test".  I guess he needs to reinstall the vacuum and superglue the cap back in place so that he can test it. 

I guess it had to happen with all of the guys parting out radios on ebay now someone is parting out tubes.

Spider tat2man?  wonder if it comes with a gift certificate to the nearest parlor?

Someone mentioned Broadcasting and tubes so thought I would take an opportunity to waste bandwidth with more stupid broadcasting stories! First a thought, if you have to work as fast as possible to change the tube that stations is more than likely a cheap low budget operation being almost every broadcaster has a axillary transmitter, not that it always in working order. Many years ago I had to replace the modulator tubes in this little dump of an AM only station, WKEN and they wanted a rush job because the auxiliary transmitter an old gates also had all bad tubes in it and did not work. The thing was they did not have the tubes on site and told me that they would call the minute they showed up, and warned me that when they expected delivery they were going to lock all the doors and act like no one was in the office in hope that the delivery company would leave the tubes there without them having to sign for them so they could claim that they never received them and get a second set for free. Was told that if that worked they would call once they had the tubes and then open the office back up, don’t know if there plan worked out or not. Second story, back at the beginning of time when I was in High School I also helped out at an AM/FM combo in town and got a call one night after midnight that the chief had removed all the 833 tubes from the Gates BC-1 and after putting them back the transmitter would not go back on air. As soon as the plate was turned on it thru an overload. So I drove my old 70 duster over to the station and we started to try to resolve what was going on and after looking around discovered that the chief had installed one of the 833 tubes backwards with grid and plate pins swapped. Funny thing was that after turning the tubes the correct direction it came up and worked with no issues so putting full plate on the grids did not hurt them. The 833 is a wonderful bottle and have three in my RCA on 160 with tons of spares and have several dead 833 around that I give out to people because they all like the looks of that huge bulb. Don’t know how to go about doing it but that would be a good envelope to cut open and make a little aquarium or terrarium in one. Think there is some stupid show on one of the cable networks where they build aquariums in things; old tubes may be a good subject.

833 = skinned rabbit look :(

73DG

The FM station where I DJ'd back in the 80s had a brandy-new 4-400A sitting on a shelf, internal structure clearly askew from being dropped or otherwise mishandled (maybe the Tube shaker stopped by?) with a big note on it that said something like "THIS IS WHAT HAPPENS WHEN UNTRAINED PEOPLE HANDLE TRANSMITTER TUBES". It disappeared shortly thereafter, probably by the culprit who got sick of being reminded.

As to 'rotating' spare tubes, that's basically nonsense and, as Jim referenced, just another opportunity for damage from mishandling. Last year I opened a pair of NIB 4-400s with 1989 date codes. Popped them in the transmitter, let them cook for a while, and (amazingly) - they worked just like new tubes!  :o  Not bad for sitting unused 24 years or so.

When it comes to spares or really any tubes, there are two kinds: Good ones and bad ones. Okay, maybe three - bad ones waiting to happen. Perhaps all tubes eventually fall into that category if not used. Aside from surplus WWII tubes like the 250TH made with lower grade materials that contaminate the vacuum over time and/or become brittle, or an otherwise-specific bad batch, I can think of no situation where a tube that was properly gettered/evacutated/sealed went bad from sitting. Mishandling? Sure.

So rotate away, Flip.  ;)

So about those 250ths and 100ths… what's you best suggestions? I have read they are pretty fragile. I am thinking STRAIGHT up, leather gloves, and safety glasses and take my time! And keep them away from Shaking Guy!

I spend at least a half hour getting my zen in place before even taking an 851 out of the carton, let alone setting it into a socket.