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Author Topic: About Vacuum Power Tubes by KK5DR  (Read 27788 times)
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« Reply #25 on: February 01, 2011, 07:48:36 PM »

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In the late 50's I was the part time evening engineer for WGBB, 813 with 811 modulators, in Freeport NY.

WOW, that must have been a home brew commercial transmitter.

I knew of one using 805 mods and 813 in the final and was said to be home brew. I wonder how they got that past the FCC?
Sorry for dredging up an old thread but sometime it's nice to do so.
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« Reply #26 on: February 02, 2011, 06:40:02 AM »

To re-iterate and cut down on the hunt for the Eimac Care and Feeding series of papers:

http://www.cpii.com/library.cfm/9
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
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« Reply #27 on: February 02, 2011, 12:35:16 PM »

It seems to me only a ham would use 811s for modulators. 812s were a better choice in broadcast service IMO. Eliminating a bias supply is over rated.
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« Reply #28 on: February 02, 2011, 01:20:50 PM »

I had an Acrodog T-348 5 kW UHF television transmitter that after it was replaced by a solid state R&S transmitter tormented me by being an almost useless aux. They used a Thompson tetrode that drew 5 volts @ 125 amperes for the filament and when you turned off the filament supply a bunch of big power resistors were switched into its primary to provide what they called "Dark Heat" 0.75 volts @25 amps. Found once that a bunch of bugs set up housekeeping in the bottom of the PA cavity because it was nice and warm while in dark heat. The Acrodog was a pig anyway and that’s the only place I have seen that. I had a couple Comark 30 kW analogs with IOT and when we had to take that off the air we ran them with beam on and no drive, still amazed you can get away with that but if you let the IOT cool down you can count on spending a hour or so trying to get it back up to operation playing around with reducing the beam and the like, I miss analog trebly. The lower power solid state digital transmitters go on and off with one little push button.

Ray F
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« Reply #29 on: February 02, 2011, 01:23:28 PM »

The CE was an old ham plus part owner and the TX was a Raytheon I believe. Who knows what he did to it but it sounded great as it played R&R and Doo Wop every night until shutdown.
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« Reply #30 on: February 02, 2011, 01:31:06 PM »

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In the late 50's I was the part time evening engineer for WGBB, 813 with 811 modulators, in Freeport NY.

WOW, that must have been a home brew commercial transmitter.

I knew of one using 805 mods and 813 in the final and was said to be home brew. I wonder how they got that past the FCC?
Sorry for dredging up an old thread but sometime it's nice to do so.

What's wrong with an old thread if the content is still interesting and relevant?  Newer isn't always better.  They have the same unexplainable hang-up on QRZ.com.  There is now a 60-day time limit on threads because people would sometimes resurrect old ones.

The broadcast engineering term for a homebrew transmitter is "composite transmitter".  I believe they are still legal to this day. You just have to build it to certain FCC specs, document everything, and run a proof of performance. The black wrinkle cabinet, meters, dials and name plates on my homebrew HF-300 transmitter came from a late 1930s 250 watt "composite" broadcast transmitter, obviously built from parts that were already "vintage" by the time it was first constructed.  Some of the original parts are incorporated in the present transmitter, but fortunately/unfortunately, another ham got to the transmitter before I did.

Fortunately, because he rescued it from the broadcast transmitter site in 1960, just before it was about to be hauled to the dump. Unfortunately, because he had zero interest in or appreciation for vintage radio equipment.  He  completely gutted the original transmitter for parts, and then reconstructed his own homebrew transmitter into the cabinet.  He worked for the phone company, so he acquired some of that ugly telephone company grey paint and sprayed it over the original black wrinkle.  

When I got it in 1970, he had dismantled his homebrew rig, and the empty shell was sitting in his garage.  He said he was about to take out the meters and trash the rest.  I swapped him a box full of old panel meters for it.  He did let me have some of the original BC transmitter parts, including the UTC LS-103 50 Hy 500MA modulation reactor, but he wouldn't let go of some of the other stuff, and he had already got rid of a lot of the rest.

I brought the remains home, and re-built my own homebrew transmitter into the old cabinet. I used my own design, using as many parts of the same vintage as the original as possible, but I didn't have any documentation on the old transmitter, so I made it into a 1 kw plate modulated rig with push-pull finals and plug-in coils, pretty much of my own mid-to-late 30s design.  I  stripped down the crudely built cabinet, re-enforced and squared it up the best I could, leaded up some of the extraneous holes the previous ham owner had drilled in the front panel, and re-painted it black wrinkle.  Unfortunately, a large stripe on the front panel didn't wrinkle, and I tried to patch it up but just made it worse.  I keep saying that some day I'll re-do the front, but it would take a tremendous amount of work to remove everything to repaint it, so that's a back-burner project that has been sitting on that back burner now for over 35 years.

Regarding 811s vs 812s, RCA recommended using a pair of 812s in the final and modulating with a pair of 811s.  I believe Gates built a 250-watt stand-by transmitter using that line-up.  Timtron showed me one at one of the sites he used to work at.  It looked more like ham radio construction than broadcast, but sounded pretty good.  811/812 series tubes probably were too small for a full time 250 watt transmitter.  A 100 watter maybe, but most 250 watters used at least something the size of 810s for both modulator and final.

According to the previous ham owner, the homebrew broadcast transmitter I just described  used three 203As in parallel in the final, driven by a single Taylor HD-203A.  The driver tube was larger than the finals! The PA was modulated by a pair of 838s.  Like 811(A)s, those are zero-bias triodes, identical to 805s but with the plate lead coming out the base instead of a plate cap on top.
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« Reply #31 on: February 02, 2011, 01:47:50 PM »

Quote
Regarding 811s vs 812s, RCA recommended using a pair of 812s in the final and modulating with a pair of 811s.  I believe Gates built a 250-watt stand-by transmitter using that line-up.  Timtron showed me one at one of the sites he used to work at.  It looked more like ham radio construction than broadcast, but sounded pretty good.  811/812 series tubes probably were too small for a full time 250 watt transmitter.  A 100 watter maybe, but most 250 watters used at least something the size of 810s for both modulator and final.

He still has it in his home but not in use. He once had it a a ski resort loaded to the power lines. He told me the whole story about that installation and how it got out beyond the grid for some miles. If I didn't have so much stuff, I would try to talk him out of it. I guess there comes a time when you just can't fit in another piece.

I didn't know QRZ was doing that. Somehow, I never got into posting over there except for a want ad for  Westinghouse parts. That worked very well. Found what I needed and then some.
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« Reply #32 on: February 02, 2011, 03:20:42 PM »

I have an R&S transister sister backup with SX-800 exciter. Instant on but only 8.5 KW TPO : (   I begged management to let me keep a 30 KW IOT for backup instead. No dice. They were sold on instant warmup.

Backup for my other station is a Thomson IOT. When I'm worried it gets run in beam mode 38 KV @ .55A just waiting to crowbar. Other than that I leave the thing cold. I scarfed some very low mile IOTs from the Alpine facility but need to hook up a Spellman or however you spell it man to keep the gas away.

Scrapped 5 Comark/Thomson/Thales cabinets last year. The 3 phase 28 volt 107 amp supplies seem to run just fine on single phase 250 volts : ) All above is UHF.

Also offed a Larcan lowband 22 KW analog and complete backup. Yahooooo.



I had an Acrodog T-348 5 kW UHF television transmitter that after it was replaced by a solid state R&S transmitter tormented me by being an almost useless aux. They used a Thompson tetrode that drew 5 volts @ 125 amperes for the filament and when you turned off the filament supply a bunch of big power resistors were switched into its primary to provide what they called "Dark Heat" 0.75 volts @25 amps. Found once that a bunch of bugs set up housekeeping in the bottom of the PA cavity because it was nice and warm while in dark heat. The Acrodog was a pig anyway and that’s the only place I have seen that. I had a couple Comark 30 kW analogs with IOT and when we had to take that off the air we ran them with beam on and no drive, still amazed you can get away with that but if you let the IOT cool down you can count on spending a hour or so trying to get it back up to operation playing around with reducing the beam and the like, I miss analog trebly. The lower power solid state digital transmitters go on and off with one little push button.

Ray F
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Mark


« Reply #33 on: February 04, 2011, 10:30:04 AM »

Where does he say he was an engineer at Eimac?  Examining his web site I get the impression he was not an engineer. He doesn't speak (write) like one.  His construction practices indicate lots of experience and skill in that area.  I also disagree with many of his conclusions and opinions, not that that's relevant to anything.
But most interesting to me is his articles lack mathematical substance. I would think that any technical information offered to the public, such as this, requires some measure of concrete numerical references be included in order to make it comparable to any other such information.  Otherwise it's just so much opinion and pretty pictures.  Pictures made less so by that stupid copyright mask. What's up with that?   





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Steve - K4HX
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« Reply #34 on: February 04, 2011, 11:19:32 AM »

He is not an Eimac engineer.

The top of the page has this:

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The info I am putting forth here comes from engineers at CPI/EIMAC, Rockwell/Collins, and my years of experience with RF power tubes.
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« Reply #35 on: February 05, 2011, 08:57:29 PM »

That's what I read too Steve. Anyway, I guess he pulled the 'nostalgia' page. I get a 404 error. I guess somebody who didn't like it got to him? 

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Bill, KD0HG
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« Reply #36 on: February 06, 2011, 11:42:23 AM »

I am responsible for a mid-1980s Harris 20 KW FM box that's now a standby. Tried leaving the filaments on the 4CX15000 lit all the time for 'instant' operation, but the tubes just didn't last when doing that. The other issue with doing that was the filament AC supply, not regulated, would zoom up from nominal 6.3 to 7 VAC with plates off, then sag greatly when the plates were turned on- The exact opposite of what you'd like to see. If I set the filament to 6.3 with plates off, then the filaments would sag to below 6 volts with plate on.

The comments were correct about wanting and needing an instant-on backup. At the time, this top-rated FM station was making $250 to $1,000 for a 1 minute spot, say 15 minutes of spots per hour, dead air becomes costly indeed. Pays for an Econco rebuild real fast.

Now we've got instant-on solid state FMs....Which seem to blow PA modules at the rate of several per year and costing more that buying rebuilt tubes ever did. Each rebuilt PA module costs about what a rebuilt 4CX20000 costs.

On the other hand, no one today--No one-- Knows how to properly and safely tune up and diagnose tube type transmitters. It's a dying art. It's much easier to swap out a module with a red light lit on it.
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John K5PRO
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« Reply #37 on: February 06, 2011, 04:25:35 PM »

You hit the nail on the head, Bill. There are very few engineers and techs coming out of the mill that know much about tubes. Ham radio experience usually helps, as they at least know how to dip the plate and peak the grid. And the newest solid state equipment doesn't have repairable parts on the boards, now it requires surface mount equipment (microscope, desoldering station, solder paste, liquid flux) to even have a chance.
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Tom WA3KLR
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« Reply #38 on: February 06, 2011, 06:56:20 PM »

I started this thread 2 years ago based on an email from a ham in the Midwest, as I recall.  I looked for the email but don’t have it now.  I was the one who stated Matt KK5DR was an Eimac engineer.  

It appears that the mistake is solely my reading comprehension error.  I have communicated with Matt today and he is not and never has been an Eimac engineer.  I have made the appropriate corrections, that I can, to this thread.
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
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