About Vacuum Power Tubes by KK5DR

[Tom WA3KLR]

Below is the link to an article on vacuum power tubes by Matt Erickson KK5DR:

http://www.kk5dr.com/Tubes.html

[Steve - WB3HUZ]

But the data is straight from Eimac's publication, Care and Feeding of Power Grid Tubes. Nothing new.

And he has this diatribe about messing with old radios.

http://www.kk5dr.com/nostalgia.htm

Such drivel coming from a guy who's web site is all about building old technology linear amps is pretty funny. Building tube amps is about 80 years behind the cutting edge.

[KE6DF]

It's interesting how some people, like kk5dr in this piece about old radios, take it upon themselves to pass judgement on how other people pursue a hobby.

I'm just getting back into ham radio after saying away since high school while making a living. I'm getting interested in AM because: 1. It's practical to build your own gear. and 2. I like the challenge of transmitting high quality voice.

I'm also interested in digital modes and plan to experiment there.

I think old tube equipment is interesting to build, and a well built boatanchor is a living, functioning, work of art.

But I also may well build a class E rig with the latest technology.

To me, there is a parallel to car collecting. Some people like collecting and restoring muscle cars from the late 60's. Others like '50's cars. Some people want everything original down to the smallest washer. Others put after market intake manifolds, electric ignition and fuel pumps and header on their cars. Still others like 1930's luxury cars like V16 Cadillacs or Duesenbergs (better have lots of money). And then there are people who want the latest BMW sports cars.

Is one type of car buff wrong, and the others right?

Is one ham wrong and the others right?

I don't think so.

This is a hobby after all -- not a paid engineering assignment.

[Tom WA3KLR]

You're right, ham radio = hobby.  When you do the same thing at work and at home there is very little distinction.

I wonder what other hobbies he has?  His only description on QRZ.com was please don't QSL.

Anyhow, some useful tips on the vac-u-u-u-m tube page.

[W1EUJ]

"Abandon all hope, ye who enter here". Memorable quote from the Divine Comedy.

If I hadn't already scrawled 'Dulcinea' on it with a fat permament marker, I'd write that on my shack door.

[W3RSW]

...and as may have been writ large on the gate overhead as gladiators entered 'boot' camp.
Glad I live in this "era."

As to the fun part of our hobby,

  Fewer and fewer of the old craftsmen that can maintain such ancient treasures are left, and only a handful remain that are even willing to do such work, not to mention the fact that parts are becoming as scarce as rocking horse droppings.

I feel honored to be of such a select few,
  as do all my parts horded away so carefully.
My rocking horse droppings doth runneth over
  with 10 ^ 8 pieces making up the lesser part of infinity.

Too bad there're at least 10 ^ 3 hoards just like, or larger than mine.

             ***************************

Wonder if ol' KK5DR's kept up on his quadrature applications and fast fourier transforms, or the myrad of applications thereof.

[k4kyv]

Most of his facts are well known, available from numerous technical sources.   However, here is one "fact" I disagree with:

Fact: Broadcast radio/TV stations keep all their final amp tubes running with filament current, at all times, for two reasons.

1. To keep the tube ready for instant use, should the other tube fail.

2. To keep internal contamination to a minimum.

Just leaving the filament running with no plate voltage will shorten the life of the tube.  An electron cloud will build up around the hot filament in the vacuum, and the magnetic field from the a.c. filament current will cause those electrons to vibrate at 60~.  The vibrating electrons will erode, or "sandblast" away the thin layer of thorium that coats the tungsten filament, destroying the emission capability of the filament.  If the filament is to be left on for long periods of time while the tube is idle, a small positive voltage should be applied to the plate or grid, to bleed away the electron cloud.

Damage from the on/off cycling of the filament can be reduced by gradually bringing up the voltage at start-up and reducing the voltage at shut down with a variac or rheostat in the primary circuit of the filament transformer.

RCA recommends reducing the filament voltage down to 80% of nominal value during standby periods that are too short to warrant turning the filament off completely.

I never heard of a broadcast transmitter that kept a spare set of tubes with the filaments already warmed up, ready for use.  Even if so, the tube would be too hot to handle when pulling out the old tube and installing the replacement.  Perhaps a spare set could be set up in sockets and filament transformers and a burn-in run periodically, so that the procedure wouldn't be necessary after replacing a failed tube.

[W3SLK]

Which “road” have you chosen for your ham radio career?

[Tom WA3KLR]

The electron cloud is your friend.  When it is built up, it protects the cathode.  With the cloud in equilibrium, electrons are also returning to the cathode.  When the electron cloud is fully depleted, this is when the surface of the cathode can be removed, causing permanent damage.

Building up of the electron cloud is what allows Class C operation, and plate-modulated Class C power amplifiers.  Ever wonder where the 2X plate current comes from at the positive peak of the modulation cycle?

The electron cloud causes a voltage drop in the tube.  This is the reason for mercury being added to rectifiers.  The mercury vapor kills the electron cloud allowing a lower voltage drop in the tube.  At the expense of this is, if the tube is asked to conduct current beyond the rated maximum, the cathode is ruined instantly.

[nq5t]

It's interesting how some people, like kk5dr in this piece about old radios, take it upon themselves to pass judgement on how other people pursue a hobby.

Aside from fiddling with amplifiers and passing judgement, he's primarily a shill for anything Icom, which is enough in itself to cause one to wonder  ....

Grant/NQ5T

[Tom WA3KLR]

If the filament is to be left on for long periods of time while the tube is idle, a small positive voltage should be applied to the plate or grid, to bleed away the electron cloud.

Don,  

This does not sound right at all.  You never want to go out of your way to deplete the electron cloud, except in the mercury vapor rectifiers as I have mentioned.  Can you quote a published technical source for this?  It sound like Hammy Hambone folklore to me.  I have never read this.

[KA1ZGC]

Most of his facts are well known, available from numerous technical sources.   However, here is one "fact" I disagree with:

Fact: Broadcast radio/TV stations keep all their final amp tubes running with filament current, at all times, for two reasons.

1. To keep the tube ready for instant use, should the other tube fail.

2. To keep internal contamination to a minimum.

 

That's not only more opinion than fact, it's factually wrong!

I've been in numerous broadcast radio and TV stations over the years. The grand total number of those who keep all their filaments lit at all times: zero.

His two reasons for doing so are laughable, as well. Like Don said, a recently-extinguished tube is too hot to handle, but there's more than just that. You do not want to apply any physical shock to a hot tube because you run a much higher chance of breaking a seal. Also, since most broadcast tubes have directly-heated filaments, there is absolutely no time whatsoever gained in having the filament warm when the tube is inserted.

Besides, these aren't 12AX7s, these babies take several minutes to remove and several more to replace. Most broadcast transmitters won't even apply filament power unless the air interlock is closed, and most cavity amps (which means any TV or FM amp) use pressure switches plumbed between the cavity and exhaust for that purpose; so it's not like you can insert the tube, light the filament, then reattach the B+ and reinstall the plate blocker. The pressure switch won't close with the cavity open! Any transmitter of decent design won't even light the filament unless it knows there's enough air across the filament seal. Any engineer who defeats an air interlock in order to satisfy this silly theorem deserves to blow a filament seal!

I'd also like to know what "internal contamination" he thinks is going to happen. It's a sealed tube, and the elements are in a vacuum. You'll get more degredation of the tube with the filaments lit than you ever will with the filaments dark. That's why transmitters have "filament hours" counters! Beyond a certain number of hours, you keep an eye on the readings because your filament emmissivity will soon begin to wane. When you get to the point where you're bumping up the screen voltage more than three times a month, it's time to swap out the tube, because the filament emission is going down and will only get worse.

Keeping a "hot spare" only means that your spare will suck every bit as bad as the tube you're pulling out! I can't beleive this guy's not only advocating something like that, but even going so far as to claim that "this is what broadcasters do"! No, we don't!

Clearly this guy's never worked as a broadcast engineer. Is he really employed by Eimac as an engineer, or just employed by Eimac? I know their standards have gone in the crapper since the Varian->CPI mutation, but to hear that someone there is making these claims is alarming.

I haven't read the rest of this guy's writeup, but I have a copy of "Care and Feeding of Power Grid Tubes" that Eimac has been publishing for years. That's mostly wisdom from the good ol' Eitel-McCollough days. Never read anything like that in there.

Sounds like thermiophoolery to me!

--Thom
Kilowatt Amplifier One Zero Grid Current

[Tom WA3KLR]

F.Y.I  I typed this in from the RCA HB-3 tube manual, front-end pages;
these tables would have been created probably involving several Ph.D.s to come up with the best over-all reliability, balancing the cumulative stress of cold start-up versus the wear-out of the unused hot cathodes.

Page titled “RECOMMENDED STANDBY CONDITIONS FOR TRANSMITTING TUBES”, dated Feb.1, 1950.
 
                              Recommended percentage of normal operating filament
                                   or heater voltage  for standby periods as follows:
Tube type by            Under 15 min.  15 min – 2 hrs.  2hrs – 12 hrs.  Over 12 hours
kind of cathode

Pure tungsten filament
Lg tubes such as            80 %                  80 %               80 %           Off
889R-A, 5592, 9C21

Thoriated-tungsten
Filament
    Small and medium tubes  80 %                  Off                   Off           Off
    Such as 813, 833A

    Large tubes, such as       80 %                  80 %               Off           Off
     5771, 5671, 5770

Oxide-coated filaments
    Vacuum tubes such as     80 %                  Off                   Off           Off
      5618, 2E24

     Mercury-vapor tubes
     such as 816, 866A, 857B   100 %              100 %               100 %       Off

     Gas tubes, such as 3B25    100 %              Off                   Off           Off


Oxide-coated Heater-Cathodes
     Vacuum tubes such as
     5763, 807, 829B              100 %               80 %                Off           Off

     Mercury-vapor tubes such
     As 5558, 5561                  100 %              100 %              100 %       Off

[John K5PRO]

I haven't ever heard of the "leaving broadcast tubes hot so they are ready instantly" idea from broadcasting or industrial and scientific applications. Now, there are times that we ramp down our filaments on big tubes, to 70-80% of normal current, to preserve emission, if we are off for a period of days, but most often we either shut them off or leave them at 100%. But we don't leave a hot spare going, that's just pouring money down the drain, or giving it to CPI, Thales and Burle tubes. As others pointed out, it is not so easy to just swap tubes in and out nowadays. In the 1930s big AM transmitters (50 kW) had a spare tube in the cabinet that was able to be swapped in, by moving some jumpers and switches.

I have been using big tubes for 33 years at work, and the AC filament "electron blasting" theory doesn't ring a bell. Never heard this. In most of the rigs, however, bias IS applied once the filament is on, so that the tube is ready for HV application at a button pressing. Our biggest grid tube, the Burle 7835 grounded grid triode, has no bias supply, and has a 30 kW DC filament. It is self-biased via a 0.25 ohm cathode resistor, developing 400 amps of cathode current and about 100 volts of cathode (grid) bias. The plant here has 44 running klystrons and about 30 gridded tubes in various amplifiers and modulators.

I read the guys website, and while some of the stuff there is factual, at least similar to what Care and Feeding says, there are some statements that are silly, or based on ??. Some of the vacuum info is that way, I won't go on to list specific examples. When I see that much truth/fable on a website, sometimes its best to just let it go and don't try and correct the poor chap. Unfortunately, some people will glom onto the words and believe everything said. Thats the beauty of the web.

As Wayne Green used to say, Caveat Emptor...

[W2VW]

FYI care and feeding has been recently updated with an added chapter on MSDC IOTs.

Current toob television transmitters will not allow the operator to run filaments by themselves longer than warmup plus 20 minutes or so depending on who writes the   gasp   software. 

If you need a hot standby the tx must be placed into beam mode. This is the equivalent of having a linear amplifier keyed and drawing quiescent current without R.F. drive(L). There are TV stations who have hot standby transmitters in beam mode 24/7.

40,000 hours is considered average life for a one eyed monster transmitter toob filament.

[Tom WA3KLR]

Yep, Dave.  The whole "Care and Feeding..." is 6 pdfs, 177 pages total.  I finished reading through them yesterday; 167 pages of actual text now.

Dave, how long does it take to warm up one of those transmitters to key up from a cold start?

The link that was e-mailed to me to look at KK5DR's "document" (which started this topic) came from a broadcast engineer in the midwest, at his station they run the standby transmitter all the time also.

[W4RFM]

Back in the day, when 833's and 4-400s roamed the radio transmitters I had to service, down south here, we would leave the filaments on overnight (for stations that signed off at midnight or whatever) so that the durned things would come on in time the next day. Also 8008 merc rectifiers were terrible to get warm without fireworks as I remmber. Many/most of the stations had un heated transmitter buildings in these states because we seldom see long periods of freezing weather. It was not at all unusual to drive out to an AM tower, and find a building just large enought to hold a Gates BC-1T and an extra yard all the way around for the engineer to get in for service. A Simpson 260, a few old tubes, the manual, one 100 watt bulb hanging from the electrical disconnect and a welcome mat to wipe your feet! Ahhh those were the days.

[k4kyv]

Back in the day, when 833's and 4-400s roamed the radio transmitters I had to service, down south here, we would leave the filaments on overnight (for stations that signed off at midnight or whatever) so that the durned things would come on in time the next day. Also 8008 merc rectifiers were terrible to get warm without fireworks as I remmber. Many/most of the stations had un heated transmitter buildings in these states because we seldom see long periods of freezing weather. It was not at all unusual to drive out to an AM tower, and find a building just large enought to hold a Gates BC-1T and an extra yard all the way around for the engineer to get in for service. A Simpson 260, a few old tubes, the manual, one 100 watt bulb hanging from the electrical disconnect and a welcome mat to wipe your feet! Ahhh those were the days.

And if you were the unmarried, 20-something chief engineer, the transmitter site with the fenced-in cow pasture antenna field, and locked gate: you had the key, made the perfect parking spot for you and your sweetie. Ahhh those were the days, my friend.  We thought they would never end...

[W3RSW]

Great stuff Don,
In my business we used well locations, same purpose 

Hey what were organizations good for anyway if not for "that special feeling."

[K1ZJH]

I must be an old fart. Back in those days we manned the AM transmitters 24 hours a day   That was when a 1st Class Phone was good for a high school kid as the summer relief for the full timers.

[k4kyv]

Weren't there any daytime-only AM stations back then?

I think it was sometime in the 50's that the FCC allowed unattended remote control for transmitters up to a certain power level.  Many of the older transmitter sites still have studio rooms, now used for storage and junk accumulation, in the building at their transmitter site, while the studios are now located down town.  Before unattended operation was allowed, the announcer on duty had at least a 3rd class commercial licence which allowed him to man the transmitter site, but not to actually work on the transmitter.  The exam covered topics like reading meters and some of the basic radio regulations, and was at about the same level of difficulty as the early Novice ham written exam.  When remote transmitters were first allowed, the announcer in the studio who controlled the transmitter still needed the 3rd class ticket.  I think they deleted this requirement when they combined the 1st and 2nd class phone into the ugly yellow "General Radiotelephone" and stopped requiring each station to employ on premises a licensed engineer.

[W2VW]

Dave, how long does it take to warm up one of those transmitters to key up from a cold start?

The 20 year old designs still have thyratron crowbars which take 12 minutes. The R.F. tube itself takes 6.

10 year old designs can go from a cold start to full strap in 6 minutes unless something is broken

[Tom WA3KLR]

Thanks Dave.  So 6 - 12 minutes off the air for those who keep the standby transmitter cold.  For those who feel this is unacceptable, run the tubes 24/7 and accept the cathode wear.  That's the two choices.

[KA1ZGC]

Given the price of a new or refurb tube vs. the price of up to 12 minutes off-air, I still wouldn't run a hot standby.

Example: a 4CX20,000 will run you about $6,000 new from Eimac, or about $2,000 refurbished. There are probably only three or four television markets in the country where you would stand to lose that much advertising revenue over 12 minutes. The filament draws 150 amps at 9.5-ish volts (nominal). That's just under 1.5kW just to heat the filament; enough to power a Class A FM station, which at least would earn that money back, unlike the hot standby.

Now, that's a 4CX20,000, which is PW compared to what a lot of the really big TV stations use, and can be easily cold-started in less than one minute. I think we can safely call that the bottom end of the scale for hollow-state TV stations. Get into thyratron/IOT transmitters, you're talking even bigger bucks per bottle.

I'm sure there are a few stations that still do the old "hot standby", but my exception was to the guy's statement that "all broadcast radio/TV stations" run a hot standby. That statement is just plain false. Back in the '50s, tubes and kilowatt-hours were cheap. That's not the case today. I know of no radio stations that run hot spares, and none of the TV stations I've been in do, either.

That's not to say there are none, but you could probably count them on both hands without having to unzip your fly.

[KM1H]

I must be an old fart. Back in those days we manned the AM transmitters 24 hours a day   That was when a 1st Class Phone was good for a high school kid as the summer relief for the full timers.

In the late 50's I was the part time evening engineer for WGBB, 813 with 811 modulators, in Freeport NY. On Saturdays I paid a friend to sit the station while I walked over to the Freeport Speedway and played stock car driver for a few hours. Never had a failure or got caught The station went off the air at midnight so I got back in plenty of time as the last heat was over before 11.

Some nights I made more money driving

Carl
KM1H