Saturday, February 25, 2017

Whatever became of Eimac?



(Wikimedia)
In my recent post, I reported some measurements on the power tubes (Eimac 3-500Zs) in my SB-220 amplifier to see if they still were serviceable after ~45 years.  (Mostly, yes.)  But this started me to wonder about the "Eimac" name, which, though once the gold standard, has largely disappeared in the Amateur Radio market.

With the help of DuckDuckGo, I was able to trace a long corporate history, starting with the original Eitel-McCullough company (1934), which became Eimac.  Then, a merger with Varian Associates, ending up as a part of Communications and Power Industries (CPI).

The good news is that, within CPI, the Eimac name still exists, and they still market power transmitting tubes.  Alas, the classic glass envelope / internal anode tubes (as shown above), including the 3-500Z, are no longer offered by Eimac.  (Some are still widely available as imports and marketed by firms such as RF Parts.)

Eimac is found in high-end markets for commercial, industrial, and military transmitters.  Glass has given way to ceramic for insulating seals, while external directly cooled anodes are the choice for efficiency and performance.  "Low end" Eimac tubes (triodes and tetrodes that are effective for our 1.5 kW power levels) may still be produced in low volumes, but they will be very expensive compared with glass envelope imports for our ICAS operations.

Over recent years, the old vacuum tube technology has been replaced by solid state designs, especially for commercial service.  So there is little demand for the kW size tubes.  Still, it's much cheaper to keep an SB-220 going with new imported tubes if needed, than to upgrade to the latest transistor amps.

Your reward for reading this far!

CPI provides a library of some of the older Eimac applications support documents.  I found "Care and Feeding of Power Grid Tubes" especially interesting.  So here are some links to the PDF files.  The basics will be interesting to ham operators, especially those of a certain age.  The advanced sections cover some fascinating large and exotic transmitting tubes that most of us will never see.


Tuesday, February 14, 2017

SB-220 Amp, need new tubes?

My station has a trusty Heathkit SB-220 amplifier for those times when 100W is not quite enough.  I don't use it a lot, but I am considering whether it's time to get a new pair of 3-500Z tubes.

The amp was built by Paul Gallier (WQ1C, now SK) in 1972.  Paul upgraded the amplifier with many of the recommended mods, including new power caps, QSK switching, bias cutoff, etc.  But so far as I know, I still have the original Eimac 3-500Z tubes.

The amplifier seems to work well, except that it's hard to get full power output on the 10 and 15 M bands.  I had data from WQ1C that suggested that he was getting fairly constant power output across 80 through 10 M at the time I bought the amp, some 10 years ago.

Time to make some measurements of my own.  Since there are a number of settings that can be twiddled, it is hard to know exactly how to make a comparison.  You can adjust drive level (Flex 6500 output), amp tuning and loading.  I settled on CW mode, with the amp switched to its low voltage "CW/Tune" setting.  I looked for maximum output power (Po) with various drive and loading settings, at the maximum allowed grid current (Ig) of 200 mA.  Po is measured with an LP-100 RF Wattmeter feeding a Drake DL1000 dummy load.

The results are shown in the figure.  I plot the DC input power (Pdc = Ip x Ep), output power (Po) and efficiency (Po/Pdc).  Clearly, there is a problem with 10 and 15 M, which show low output power and efficiency.  At 10 M, the output power has fallen by 3.3 dB -- about 1/2 S-unit.

High frequency fall-off like this is said to be a typical problem in power tubes as they age. (See W8JI's amplifier site for example.) Presumably the gas ions, being much heavier than electrons, move relatively slowly and "gum things up" with their long transit times at higher frequencies.  (I would like to find a more technical treatment of the problem.)

It's good to have data.  Now the question is whether getting back that 1/2 S unit on one band is worth the cost of new tubes.  Short of that, there is the possibility of reducing gas by "gettering" the tube -- running with high dissipation (plates glowing red!) -- which activates  a special gas-absorbing getter material covering the plates.

Note added: Running with bright glowing anodes is dramatic, but I have to wonder if it is safe for the SB-220.  The cooling "system" (fan) is rather primitive.  It seems to be OK for normal ICAS operations (plates dim if red at all), but when dissipating power at the maximum spec. (500 W) for any length of time, you have to worry.  I understand that a particular issue is cooling of the anode and base connection pins, where a sustained overheating will compromise the glass seal, letting the vacuum out.  So aggressive gettering is probably not a good idea with the stock Heathkit.  It would be handy if we had a way to measure those critical seal temperatures.

Sunday, January 15, 2017

First Meteor Scatter Contact

Meteor in a Perseids shower, Wikipedia
It's not exactly ground-breaking in the Amateur Radio world, but I'm pleased to have made my first "meteor scatter" contact with another radio amateur.  Thanks to W4IMD, Peter in Georgia, who exchanged information with me over a path of about 1,100 miles on 50.28 MHz with about 50 Watts of power.  We used the software mode called "MSK144", developed by friend and colleague Joe Taylor (K1JT).

Meteors strike the Earth's atmosphere frequently, even in the absence of a big meteor "shower".  They generate a trail of ionization that lasts up to a minute or so (at 50 MHz), which is sufficient to exchange a bit of information between ground stations that have mutual visibility -- up to about 1,300 miles.

Strong meteor burst from N0TB in Minnesota displayed
on FlexRadio FLEX-6500 SDR transceiver
There are other worlds to conquer: working through Amateur Radio satellites or the ultimate in weak signals -- moon-bounce communication. All these have been done one way or another for decades, but they keep me learning new tricks!

Monday, December 26, 2016

A network benchmark update

Previously, I've posted several Comcast / Xfinity's benchmarks for our CATV Internet service.  (Click on "Benchmark" topic at right.)

Lately, the IPv6 service seems pretty reliable with my system.  That was a problem for some time.  It may have been a bad interaction between the Comcast plant and my local routers, but it just went away.  It may have been a Comcast reconfiguration that helped us, but it also could have been an Asus firmware update. I am now running ASUSWRT-MERLIN firmware on the Asus RT-N66U router, which I can highly recommend as an expanded and improved version of the Asus distribution.(It cured a long-standing issue with JFFS2 overflow.)

Again, I highlight the DSL Reports speed test, which checks your "real world" network performance, including the dread "buffer bloat".  Today is Boxing Day (Dec. 26), and DSL-Reports is giving me a so-so report and a good report. Here they are, separated by half an hour:


The variability may be partly due to the speed test's different selection of test hosts.  But it may be something real about Comcast or the Internet "weather".  These tests use IPv6, it appears.

For comparison, between these two tests, Comcast's own speed test shows this:


This is the available speed within the Comcast network, which seems to be the best possible result -- not fully representative of what you experience with a random Internet connection -- even if the server is fast and well-connected. (Note that the driving distance from Branford CT to Boston is really about 144 miles, not under 50. Go figure.)

Thursday, November 24, 2016

Prefixes I have known (WPX)

Recently received some more wallpaper, attesting to the number of "prefixes" I have contacted on the Amateur bands over 50+ years -- 550 Digital and 600 total.  (There are a lot of prefixes out there.  AA6 is different from AA7, etc.)  Digital contacts include RTTY (radio teletype), PSK31 (phase shift keying), and (mostly) JT65/JT9.




Wednesday, November 16, 2016

Saturday, August 06, 2016

Windows 10 "Anniversary Update" & Ham Radio

There are 3 Windows 10 systems in the house.  I chose the least important one (a Toshiba laptop) to be the first sacrifice for the latest Microsoft update.  These updates are big deals.  This one took nearly 2 hours start to finish, and it had me go through the new installation checklist to decide what data gets shared with Redmond.  (I generally minimize that, hoping to keep a smidgen of privacy.)

The good news, apart from the long waiting for things to complete, is that my laptop is back to what it was before. Supposedly, there are benefits in the user interface -- more Cortana, etc., but they can be ignored fir the time being.

The truly worrying part of Windows evolution is that MS is asserting ownership of my data and my computing life in more and more ways.  In the name of "convergence", my PC is morphing into a cell phone, and I find myself slipping into the MS walled garden.  Why, it's enough to keep me on Linux for most of my work!

Unfortunately, I do need to keep Windows around for my Amateur Radio operations -- running the Flex 6500.  That is my "big" computer.  It will be the last one to be updated, given that the Flex software may need special TLC when there's a major Windows update.

Monday, June 20, 2016

IPv6: Things that fix themselves

In a January post, I commented on trying to make the new Internet Protocol (IPv6) work in my household.

Despite some detailed sleuthing, I could not get IPv6 working reliably on my WiFi/Ethernet local area network with its connection to our ISP, Comcast.  The router would give up after a day or so, reporting ICMP6 checksum errors and shutting down IPv6 service.  (IPv4 worked well, regardless.)

I had tried swapping out a lot of my devices, including routers, but nothing seemed to keep the service going for more than 24 hours.  Lacking more elaborate packet inspection tools, I put the whole thing on the shelf.

Now, after 5 months of computer / Internet life, I thought I'd check in again.  What do you know -- IPv6 is stable now.  There have been quite a few updates to operating systems, routers, and other components since January, so it's not possible to say what made the difference.  And Comcast may have secretly changed its service in a way that cured my bug.  (The log still reports bursts of ICMP6 checksum errors, by the way.)

We may never know what happened, and that's a shame because it is good to know where the weak links are (or were) to help plan future developments.

Meanwhile, laissez les bon temps rouler!  We are ready for the next century.

p.s. This is mainly a hobby activity.  There is practically nothing you can do with IPv6 that you can't do with the common IPv4.  (You can test your own IPv6 capability here.) Over time, since the IPv4 system is now almost out of available new addresses, new services will have to be provided on IPv6 only.  But that may be a while yet.

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