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#1
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Solid state transmitters are notoriously finicky about matching to the
antenna. Tube equipment is not, so I am told, and early experience seems to bear that out. Certainly I can see one of my newer rigs start to fold back at 2:1. What are the practical limitations of the Tube finals apparent flexibility? Is it safe to compare the load, plate, and drive controls to some of the functions of a tuner? (possible real dumb question) - 73 de Mike KB3EIA - |
#2
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On Mar 4, 9:48?am, Mike Coslo wrote:
Solid state transmitters are notoriously finicky about matching to the antenna. Tube equipment is not, so I am told, and early experience seems to bear that out. I disagree some with that, having entered HF radio comms QSYing 1- to 15-KW transmitters. Failure to properly neutralize a final RF amp can result in heating sufficient to melt the glass envelope enough to let air in and thus destroy the tube (an 833 that was mounted on the control console at Army station ADA for weeks as a reminder). Certainly I can see one of my newer rigs start to fold back at 2:1. That's a somewhat arbitrary level that is designed into most solid-state PAs. One can run them without the VSWR sensing but it isn't a good idea. For one thing, RF power transistors are expensive and replacement is not the relatively easy task of just unplugging the old tube and plugging in the new one. It's a mechanical task and one has to remember to properly heat-couple the new PA transistor...the amount of waste heat is concentrated in a much smaller space than big tube envelopes-bases. What are the practical limitations of the Tube finals apparent flexibility? That's in many decades of old literature and covered extensively. Data from commercial service transmitters is more comprehensive than amateur types as a general rule. Some of that may be hard to get now. Is it safe to compare the load, plate, and drive controls to some of the functions of a tuner? (possible real dumb question) Not dumb, it's more like comparing potatoes and peas. The long-common tube tuning controls are directly connected to variable, relatively narrow-band tuning and impedance-matching passive circuits. The tube plate source impedance is relatively high compared to the antenna feedline, even if that feedline is 600 Ohms balanced. The common pi-network is both a resonating network and an impedance-changing circuit. An antenna tuner is very simlar to a tube pi-network but operates either to change (narrowband) impedances up or down relative to the feedline characteristic impedance. Again, passive components do the work of transformation. By contrast, most of the solid-state power amplifiers are broadband, much more so than common tube circuits. Since their input-output impedances are relatively low and known (and predictable) over a wide frequency range, they can use broadband transformers for matching. The end result in the design is one without many of the tube controls' necessity. Usually, but not always, either type of amplifier is still suceptible to damage from mismatching load impedances. The mismatching just takes on a slightly different form between the two. 73, Remember: All electronics works by smoke. If the smoke gets out, it won't work... :-) |
#3
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" wrote in
ups.com: Failure to properly neutralize a final RF amp can result in heating sufficient to melt the glass envelope enough to let air in and thus destroy the tube (an 833 that was mounted on the control console at Army station ADA for weeks as a reminder). I would also suspect that when dealing with 15 KW transmitters, errors would be pretty unforgiving. What are the practical limitations of the Tube finals apparent flexibility? That's in many decades of old literature and covered extensively. Data from commercial service transmitters is more comprehensive than amateur types as a general rule. Some of that may be hard to get now. I'm going to have to try to find some of the literature. Remember: All electronics works by smoke. If the smoke gets out, it won't work... :-) Thanks much Len - I'm digesting the info now. I know it seems a little strange to become interested in tube equipment at this late stage, butour hobbies sometimes take us in strange directions. 8^) - 73 de Mike KB3EIA - |
#4
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On Mar 4, 3:56�pm, Mike Coslo wrote:
" wrote roups.com: * *Failure to properly * *neutralize a final RF amp can result in heating sufficient * *to melt the glass envelope enough to let air in and thus * *destroy the tube (an 833 that was mounted on the control * *console at Army station ADA for weeks as a reminder). * * * * I would also suspect that when dealing with 15 KW transmitters, errors would be pretty unforgiving. What are the practical limitations of the Tube finals apparent flexibility? * *That's in many decades of old literature and covered * *extensively. *Data from commercial service transmitters * *is more comprehensive than amateur types as a * *general rule. *Some of that may be hard to get now. * * * * I'm going to have to try to find some of the literature. Besides old ARRL Handbooks prior to the 1970s, I'd suggest finding the site that has digitized copies of GE Ham News. Those were (bi-monthly?) hand-outs by GE to push their tubes (naturally) but they contained lots of different ham projects (using tubes, of course). I found such a site a few years ago but didn't bookmark it. Was incomplete then but being worked on. The 1960s was a good peiod for new designs in USA amateur radio. I used to grab my boss' copies as soon as he was done with them back then. :-) 73, Len |
#5
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" wrote in
oups.com: Besides old ARRL Handbooks prior to the 1970s, I'd suggest finding the site that has digitized copies of GE Ham News. Those were (bi-monthly?) hand-outs by GE to push their tubes (naturally) but they contained lots of different ham projects (using tubes, of course). Got it! Thanks a lot Len - I googled them up, and have enough reading material to keep me busy for a while. the site is: http://bama.sbc.edu/ge_ham_news.htm - 73 de Mike KB3EIA - |
#6
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From: Mike Coslo on Sun 4 Mar 2007 22:56
" wrote: Besides old ARRL Handbooks prior to the 1970s, I'd suggest finding the site that has digitized copies of GE Ham News. Those were (bi-monthly?) hand-outs by GE to push their tubes (naturally) but they contained lots of different ham projects (using tubes, of course). Got it! Thanks a lot Len - I googled them up, and have enough reading material to keep me busy for a while. the site is: http://bama.sbc.edu/ge_ham_news.htm Thanks for the reminder on BAMA contents. BAMA has more than just old tube equipment manuals. :-) Good site! On the general subject of tube PA matching to load, some remarks: The automatic antenna tuner might have its beginning at Collins Radio of the 1950s decade. Reference is the T-195 transmitter, part of a set that used the special version of the R-390 series called the R-392, designed and built for the USMC, first fielded in 1955, intended to be Jeep mounted. The basic whip antenna matching was a servoed single variable L and a single variable C to a conventional PA output tank...so-called Ell-network, switchable to the four possible L-C connection possibilities. On an Army demo in late 1955, I was most impressed when the demonstrating officer simply removed half of a whip section (!), hit the tune function, and the servo system re-tuned to this new antenna impedance in seconds. :-) Warren Bruene must have had a hand in that Autotune labeled antenna matcher because it has the first instance I've seen for the "Bruene detector" in the transmission line to get both amplitude and phase of the RF. Slight variations of that exist today, generally with a toroid for current output and a small capacitor for voltage output, both combined into dual diode detectors. Today's antenna auto-tuning subsystems use binary-progression switched single inductors and single capacitors with the servo system basically a microcontroller plus small frequency counter (sometimes) that can determine which L or C to switch and remember the frequency and setting. SGC (Stoner Goral Company) in the Puget Sound area of Washington state has at least three models for both maritime and amateur radio HF use. The Big3 (Icom, Yaesu, Kenwood) have them, either built-in or as out- board boxes. Several independent USA companies have them. ALL (no exceptions) antenna tuners have limits on their impedance matching capabilities, whether "Pi-L" output tanks or big boatanchor style structures that look very impressive. There are few overall advantages in any configuration with the possible exception of Simplicity of the single L, single C variety now common to today's autotuning matchers. ALL, even the popular Pi-network, have limits that can be proven mathematically; if the math doesn't fit, no amount of publicity or historical references will make it fit better. If you or anyone else would like an algebraic-only math explanation of the four combinations of single L and C matching combinations...with their limits of load impedance variation, I'll be happy to forward them by e-mail attachments. No binary files here and the equations, figures are better shown in the PDF format. 73, |
#7
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On Mar 4, 10:56 pm, Mike Coslo wrote:
the site is:http://bama.sbc.edu/ge_ham_news.htm Mike, If you like the BoatAnchor Manual Archive, you may be interested in these sites. Lots of downloadable manuals and data: First is Pete Millett's book site: http://www.pmillett.com/tecnical_books_online.htm Has some incredible stuff, like complete ARRL and Radio Handbooks, Radiotron Designer's Handbook, Reference Data for Radio Engineers, and much more. All in PDF. CAUTION! Some files are quite large, and will take a long time to download via dialup. One trick I have used is to set up a dialup download late at night, hit the button and go to bed. and tube data, from the RCA HB-3 books: http://www.pmillett.com/hb-3_tube_manual.htm arranged by inidvidual tube type, for easy download. The Glowbugs website has lots of downloadable info: http://www.mines.uidaho.edu/~glowbugs/index.html including some good manuals and articles on WW2 military surplus: http://www.mines.uidaho.edu/~glowbug...__Surplus.html http://www.mines.uidaho.edu/~glowbugs/PDF%20files/ Some of these are quite large, too. "Bunker of Doom" site with lots of stuff: http://www.bunkerofdoom.com/ Tube manuals, for example. Transformer catalogs and other data: http://www.bunkerofdoom.com/xfm/index.html Another good site: http://www.antiqueradioarchives.com/archives_index.htm 73 de Jim, N2EY |
#8
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On Mar 4, 12:48?pm, Mike Coslo wrote:
Solid state transmitters are notoriously finicky about matching to the antenna. Tube equipment is not, so I am told, and early experience seems to bear that out. IMHO, it's really a matter of the actual circumstances. As far back as the late 1950s there were hollow-state ham rigs made that were meant for 50 ohm loads only. In fact, there were some HF tube ham rigs made that required no conventional tuneup at all (CE 100V, 200V, 600L). Certainly I can see one of my newer rigs start to fold back at 2:1. Most hollow-state ham rigs can handle 2:1 SWR no problem. Sometimes there is less tolerance for loads that are highly reactive, though. What are the practical limitations of the Tube finals apparent flexibility? It's really a matter of how the rig was designed. Many 1950s hollow-state ham rigs were built with pi-networks that could match a wide variety of loads efficiently. The EF Johnson Viking 2 is a classic example of that type. Many homebrew designs also had such pi-networks. The problem is that the components for such a wide-range network tend to be large, heavy and expensive. So in the late 1950s and early 1960s, rigmakers designed more for compactness than for wide matching range. Still, the typical ham rig of those days could usually handle SWR of 2:1 or less with no problems. Is it safe to compare the load, plate, and drive controls to some of the functions of a tuner? (possible real dumb question) Not a dumb question at all IMHO. The short answer is "no". Tuning up a hollowstate ham rig is a similar but not identical to adjusting the typical tuner. Some may tell you that all it takes to tune up a tube transmitter is to "peak the grid and dip the plate", but that's simply not correct. Tuneup procedures vary according to rig design and you have to be specific. Of course once you get the hang of it, the procedure rapidly becomes second nature. What specific hollowstate rigs are you considering? 73 de Jim, N2EY |
#9
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On Mar 4, 12:53?pm, wrote:
On Mar 4, 12:48?pm, Mike Coslo wrote: Some may tell you that all it takes to tune up a tube transmitter is to "peak the grid and dip the plate", but that's simply not correct. Tuneup procedures vary according to rig design and you have to be specific. Sorry, but that was procedure for pre-WW2 high- power HF transmitters. While it is a simplistic phrase, it still applies. A more exact procedure was to tune up the exciter with reduced drive power and literally peak the grid current. Plate current was then observed with the plate tuning adjusted for a slight, but observable dip in plate current. Of (perhaps) greater importance was setting the neutralizing control for minimum grid current; "dipping" the plate current should produce the least grid current peak on adjusting the plate tuning. For best results on setting the load-side capacitor of the common pi-network without a bidirectional power meter, a detector way out in the field with meter next to the transmitter is the simplest way to "tune" that capacitor. However, with about 34+ other high-power transmitters all in the antenna field, that is impractical; presets for that control would suffice. The load capacitor of a pi-net has the least effect on tuning to a new frequency. When someone does about two QSYs per shift on at least 15 different transmitters with pi-network output circuits (all with vacuum tube PAs), yes, one "gets used to it" but what I described was the correct phrase. The pi-network has been around and used in HF transmitters since at least the late 1930s and has survived past the start of the semiconductor era. However, the convenience of broadband transistor power amplifiers has pretty much tossed that whole tube tuning procedure. Used with a Bruene detector sensor for an automatic antenna tuner, it makes QSYing a snap, even jumping bands (with a broad- band antenna, of course). "Peak the grid and dip the plate" is an old correct phrase. It will be found mentioned in the current US amateur radio question pools. Yes, there are exceptions. I was once involved with a distributed amplifier design that would cover over an octave of spectrum using tubes and was NOT tuned at all in normal operation. Since that one involved over a dozen vacuum tubes (ceramic-metal medium-power types), it would not be suitable for ordinary amateur radio HF transmitter stations. The vertical amplifier of the old Tektronix 54n series oscilloscopes used push-pull tube-type (all glass envelope "receiving" type) distributed vertical deflection amplifier. The pi-network output circuit was a favorite among amateur homebrewers for decades due to its simplicity and better ability to attenuate harmonics, that coming to be more and more prominent in regulations as HF users became more plentiful. |
#10
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On Mar 4, 11:21 pm, "
wrote: On Mar 4, 12:53?pm, wrote: On Mar 4, 12:48?pm, Mike Coslo wrote: Some may tell you that all it takes to tune up a tube transmitter is to "peak the grid and dip the plate", but that's simply not correct. Tuneup procedures vary according to rig design and you have to be specific. Sorry, but that was procedure for pre-WW2 high- power HF transmitters. Sure it was. While it is a simplistic phrase, it still applies. A more exact procedure was to tune up the exciter with reduced drive power and literally peak the grid current. Plate current was then observed with the plate tuning adjusted for a slight, but observable dip in plate current. Of (perhaps) greater importance was setting the neutralizing control for minimum grid current; "dipping" the plate current should produce the least grid current peak on adjusting the plate tuning. A number of amateur transmitters/transceivers have used a quick peaking of the drive/preselector control followed by adjustment of tune and load controls for maximum output, keeping readings within operating parameters. I've never seen an amateur transmitter with a front panel neutralizing capacitor. Neutralization is normally a set and forget procedure which one needn't worry about until the final tubes are replaced. Tuning for maximum output for a given amount of drive has become the norm in tuning high power, vacuum tube linear amplifiers. All one needs do is make certain that the bottles don't aren't drawing too much grid current. A check of linearity can be made with the station monitor 'scope. The load capacitor of a pi-net has the least effect on tuning to a new frequency. That would depend upon the antenna being used and the amount of frequency change as well as the type of equipment being used. Some manufacturers switch in some fixed capacitance on various bands or portions of bands. The pi-network output circuit was a favorite among amateur homebrewers for decades due to its simplicity and better ability to attenuate harmonics... ....but the Pi-L did a much better job of attenuating harmonics with only a little more circuit complexity. Quite a number of Novice licensees found themselves in receipt of OO notices or letters from the FCC when using a simple pi-net output tank with a multiband antenna. Dave K8MN |
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