A Look at a 1950s-era AM Radio Transmitter 

I maintained a 1946 vintage 5G at WSGN-AM in Birmingham, Alabama in the late 70s. True story, I was troubleshooting an air flow issue in the blower cabinet when I noticed something flat and square was partially blocking the blower intake. I reached in and pulled out a 12" LP, still in its brown paper studio sleeve, dated 1964. It was a pristine copy of 'Meet the Beatles' on Vee Jay records that one of my predecessors stuck in the transmitter 15 years earlier. No Idea why he would do that. One of my colleagues related how he learned of the assassination of President Kennedy while he was logging the transmitter meter readings. He clearly heard the news bulletin via the sound emitted from the modulator cabinet.

Especially given the fact that this transmitter is in perfect operating condition, I certainly hope that you can take steps to prevent this from ever being dismantled and thrown away. I recently had been forced to dispose of a GATES BC-5B that could have easily been put back into service. Great job on keeping this alive and thanks for such a wonderful video.!

In the early '70s during college, I worked a 16 hour weekend shift as the transmitter engineer for a 50kw day/ 10kw night AM station. Our day pattern fed 2 towers and went to 9 towers at night. The daytime transmitter was an RCA Ampliphase BTA-50G. As I recall, the power supply used 6- 857B MV rectifiers that were almost 2 feet tall. It ran at about 16KV at 4 amps. The blowers on that thing were really loud. Unlike a typical plate modulated transmitter, this was essentially 2 phase modulated transmitters with a network on the output side that vector summed the phase shift of the 2 transmitters so as to create an amplitude modulated signal to the antenna. We needed to be sure not to exceed 100% modulation, or the result would be horribly distorted audio. The transmitter tubes were huge and required a lifting device to change them. Luckily I never had too. The doors on the power supply cabinet had spring loaded shorting bars that would discharge the capacitors if the door opened. Get ready to change your underwear if you weren't expecting a loud snap. The night transmitter was a plate modulated RCA 10D from the 1930s that was retired from use by the state police when they used to operate near the AM broadcast band. This thing was like a giant ham transmitter in that tune up and operation were the same. There was a huge modulation transformer that sat in a cage behind the transmitter. It also had 2 large brass balls to form a spark gap for over modulation. This transmitter had no forced air cooling and it was a dream to take that 50kw unit off line at night. You could hear the modulation transformer and it sounded like a tweeter. The inductors it the antenna tuning huts also acted like tweeters. I had a lot of fun working at this station and really enjoyed your video of the well preserved 5G.

As a little kid, I used to dream of working on radio transmitters, and that every visit to the local radio station and seeing the transmitters operate in full power was a thrill.

As a young man, I used to help the station engineer at the remote transmitter site out in the sticks when lightning repairs etc. required some overnight work. He was a polio victim with leg braces and often needed some extra help. The 1KW transmitter used two 4-400 RF output tubes. I was a ham and he would let me have some of the older 4-400 tubes for my 1KW ham rig. Those were the days. I once volunteered to climb the tower half way and replace a burned out light. I will never do that again. My legs were like jello afterwards. Fond memories.

You’re a good guy to show that beautiful old rig. Love the shag carpet trim.

I made a 200w AM broadcast band transmitter for my neighbour and I, we have a huge collection of old am radio, but since there's no station where I live, I made one myself and I run the audio from a tube amplifier connected to my computer with a digital am compressor. It has 2 807 in the final rf amplifier, class C plate modulation. It's a smaller version of this one. It really sounds like a commercial radio. We don't have any neighbour around so I don't have to worry about bothering others people. The antenna is a radial half wave long wire. It runs very well. I used a all tube design because it's easier and I have plenty of parts.

Marvelous transmitter. KUGN (Eugene) ran the very similar BTA-10, operating at 5kW, thru 1978 when it was replaced by a Continental. Amazingly solid, good sounding, and reliable. Also easily capable of 110% to 120% positive given the oversized components.

That RCA transmitter is a true American Machine. Beautifully made, simple, reliable, serviceable, and it might last as long as you can get tubes for it. Plus, being crystal controlled, zero phase noise! A super clean transmitter signal is the result.

keep the old transmitter going mate. as for the unhappy Harris, you are more than welcome to send it to me

I enjoyed your tour of this transmitter. You voice and laughter conveys enthusiasm and positive tone. I worked for an AM station in Topeka Kansas. KEWI back in the early 70s which used a Collins 21E. We used mercury vapor rectifiers in the hi and Lo voltage power supplies. Modulation would really get those guys a blinking. They later went to solid state rectifiers.

Wow, this takes me back. I worked at a station in the late 70's, that was using a 1 KW Raytheon, (1947 vintage), at night, directional 4 tower array. Daytime, we used an RCA BTA-5, non-D. The RCA BTA-5 was only 2 units though. There wouldn't have been enough room at the transmitter site for that mega-monster 5KW that you showed here. I was one of the jocks at the station, but was at the x-mitter site on many occasions. It was nice to take a trip back to the fun old times of radio. I got paid crap, but I had fun.

Those tubes you were talking about looking at -- they do put off some UVB and UVC, but even that thin glass plate in front of it would completely absorb all of it. Even the glass of the tube itself probably absorbs the vast majority of the UVC. So I wouldn't worry too much about it. You could always grab a UV sensor from Adafruit and take some readings. Anyway, this thing is absolutely awesome. I would love to hear this thing actually on the air!

I worked in a radio station many years ago that had a Gates BC-1 transmitter. Our running joke was, we didn't know if that was the model number or the year it was built. It had two 807's and four 833's. The unit was about the size of a large refrigerator. We could always tell when trouble was brewing in that monster when one or more 833 would start glowing a VERY bright orange.

It's amazing how something like this is still considered a technological marvel.

I am amazed to see one still working! I used to work on a RCA BT10K 27 years ago when I started in radio business.... Same design almost. And we had a Harris MW1 iKw as backup. Thanks for the video!

About 20 years ago I got the unofficial B tour of a long time popular AM radio station's backup transmitter while working on a cell site nearby and chatting up the engineer for the station through the fence during a smoke break. Similar equipment and vintage. They kept it operational rather than installing more modern equipment since it was there, still worked, parts were still available and it was easy to maintain. A few months later a small plane crashed into their new tower at their new location and they had to fire up the old one and operate from it for months. Their newer site had more power but their old site had high elevation. During their back up operation I was working on another cell site a good 900 miles away and I was able to pick them up on my truck radio at night no problem. I live about 400 miles from there now and I can tell when their new site is under maintenance because I can pick them up here day or night while they are on their backup.

very cool to see another old rca transmitter operating. in my state we also have a functional old rca transmitter, a bta-50f from 1945 installed on vashon island in washington and operated by komo am 1000. it's so big it has man doors on it and you walk around inside of it to service it.. it's a massive beast.

My dad was a chief engineer at a AM station in early 50's and I remember as a kid going out to the transmitter with him to check on things. Mainly remember the tremendous heat coming out of the equipment. Thanks for the video!

Radio stuff isn't one of my interests, but this is still a really cool piece of kit even if I don't understand 90% of it. Thank you for taking the time to give us this tour and demonstration!

I started in radio in 1967 (on FM) and by the time I 'worked up' to AM, these were no longer around. I often wondered what they looked like and you showed in great detail what I have long wondered. I bet I would have gotten along well with that old girl. I was in the room with one 30 years ago and still remember hearing it 'singing' the Children's Marching Song by Mitch Miller. It was an honor to be in the same room. Thanks very much for taking the time to walk me through the innards of this majestic transmitter.

I love that 90% of the exposed circuitry would fry you as surely as a fish stick in a toaster oven

Thank you for showing us this awesome grandaddy of a transmitter it was absolutely fascinating to see you start it up! I used to listen to AM radio a lot as a child here in the UK (we had a few pirates) and have always been fascinated by AM transmitters and how they operate. The running hours is staggering when you do the math. 507125 hours is 21130 days or a staggering 57.89 years 😳 Hearing the audio resonance from all the components within has a real charm to it and it deserves to run forever.

That was really cool. One of these things most people will never get to see in person or work on. Something so cool about tubes and analog electronics though, how you can actually see and hear it work.

Wow, what a great tour, thank you. Back when radio had some soul.

I liked this video alot, very well made it honestly felt like i was getting a tour from someone who really knows and enjoys the place

Love it!!! Run it on the air and play some Wolfman Jack!

Thank you. They don't build anything like they used to anymore. As for the beast at WQXR in NYC long gone is that trusty Westinghouse 50HG-2 Transmitter, and same as you have found out, A Harris 10K stand by back up was so unreliable very temperamental. By the way, Modulation Transformer and Reactor were almost as tall as me. And I stand 6' and every now and then you would get a SNAP sound as the arc gap on top of that reactor went off. 😂 This was a great video of day's gone by. Today's transmitter sites both AM, FM, and TV have no soul or humans standing watch 24/7 gone is an era I will remember. 👍👍

About 1979 I got hired as a transmitter engineer at WARM "The Mighty 590" in Avoca PA. Actually I didn't know anything, I was a college freshman and newbie Ham radio op. In fact I think maybe a Ham Op got me the job? The transmitter was basically 5 towers out in a farm field miles from the studio. I never saw the studio. Fun job while it lasted which wasn't long. The owners replaced most of us transmitter baby-sitters with automation. I wish I had taken some pictures of the facility but I didn't have a camera (and of course that was before the era of smartphones with cameras- or even 'dumb phones") Thanks for the transmitter tour.

I worked on the preceding RCA model (BTA 5F) installed in circa 1947 at 620 kc in Knoxville and a following model, the RCA (BTA 5R) installed in 1959 at 1310 kc in Asheville and both were built very well and very reliable. (Between the 5G and 5R models, there was the 5H, which was a 5G with a beefed up plate transformer, and the 5J and 5L, which were the 5 KW versions of RCA's Ampliphase design,.) I installed a new Collins transmitter in Knoxville and literally gave the 5F away. At the time (about 1980) I did not see the beauty of the 5F, but looking back it was a huge mistake not to keep it as a backup (we had a newer transmitter to backup the new Collins rig). Also, it was almost whisper quiet due to the large cooling fins on the 892R final tubes not needing a high pressure blast of cooling air. The 5F worked perfectly, but even in 1980 it was very inefficient, but it could have been left in service as another backup and would probably still be viable today unless it lost a transformer, especially the modulation transformer which was known to fail on the 5F. Plate voltage on the 5F was 18,000 volts due to the low current capability of the 892R tubes which stressed the mod transformer. I imagine the tubes for the 5F became difficult if not impossible to get; we were using rebuilt tubes from Freeland (which was later bought by Econco) in the 1980's and I do not see 892R on Econco's list of tubes they have available. The 5F still had the MV rectifiers up to 1980, but the 5R had the 8008's replaced with silicon rectifiers sometime in the 1960's Both the 5F and 5R used a conventional three phase rectifier for the HV, which IMHO are much more reliable, but did not give the ability to control the power as finely as the thyratrons did. The thyratrons seem unnecessarily complicated to me. I guess RCA also decided that when they came out with the 5R. Like the 5G in this video, the 5R used a pair of 5762s in the RF amplifier, but used 3X3000F1s for the modulator, which I think probably was probably a better choice of tube for that purpose. The drivers were completely different, a pair of 4-125As each for the RF and modulator. Don't know what became of the 5R at 1310 as I sold that station in 1986. BTW, in 1969-1970 I lived in Western New York and had an occasion to visit WSAY back then. If my memory is correct, the 5G was what was on the air and it sounded like it needed the modulator tubes to be replaced. For the way the station looked back then, and the way it sounded (appearing to not be very well maintained) this 5G is in really good, and clean, condition! I hope the owners of the station keep it in service.

I love the blue glowing tubes!! Also, great use of Photonicinductions sayin!

I wanted to be a radio engineer. At 13 I had my 3rd class FCC license. Then I was installing radios in cars. Cars became my passion. Retired an ASE master technician. Wish I stuck with radio, my back would be in better shape. Thanks for the tour.

Several years ago, I took a tour of the transmitter site of CFRB, Toronto. It's a similar vintage transmitter that runs 50 KW. There's a bit of history in it's call sign. CFRB was founded by the Rogers Vacuum Tube company to promote the company's batteryless receivers. Ted Rogers invented the indirectly heated cathode, which mean a battery for the heaters was no longer needed. Hence the letters R(ogers) B(atteryless) became part of it's call sign. This Ted Rogers was the father of Ted Rogers Jr., who founded Rogers Cable and was owner of several TV & radio stations, a cell phone network and more.

This is waaaaay cool. Into electronics, but unfamiliar with transmitter rigs. Did a great job - thanks!

Very cool, it's nice to see the old equipment still up and running. Thanks for sharing.

Wildly cool to see something like this thats still in use, or at least kept in working condition as part of a commercial venture. I love it.

Good old AM miss them days makes me think about having fun with just a AM Philco Ford Transistor pocket radio

I thoroughly enjoyed your tour of the transmitter! Great job.

Amazing piece of equipment, they don’t build to last like this one anymore. Thanks for the tour. 👍👍

Kudos to the owners for not dismantling the RCA

What a great tutorial! Thanks for posting this

Very nice presentation! I like you style of presenting -- held my interest...

My first job out of high-school was w/KFYO AM in Lubbock - which had one of these same RCA transmitters (5KW). Fantastic video - thanks for sharing!

Thanks for this video, absolutely fascinating!

This. Is. So. Cool. I've been looking for videos like this. This hit the spot. Thanks for posting!

Thanks for the tour of the time capsule which included the bonus shag carpeting on the wall from the 70s!

absolutely fantastic video! it is very important to preserve this knowledge and it's good to see someoe like you doing it. Keep up the videos, you do them VERY well and there could never be enough. Especially cool stuff like this.

What a flashback! I started in radio back in 1983, halfway through high school... I recall having to make an 11-mile drive into the river bottoms to replace blown fuses at our remote transmitter site (on stilts even) when they'd blow... Nope, I couldn't tell anyone what that AM transmitter model was but I spent quite a lot of time in that decade (83 to 93) watching while our engineer worked inside our boards or the transmitter stand in the studio. I returned to radio in 2001 and 2002 (almost two years exactly) and found the thrill and art was gone but the technology was no less fascinating to me. Gone was the odor of burned dust on tubes but still interesting... Thanks for some pleasant memories from a past life :)

Great video, thank you for showing and explaining!

I worked at a station that had one of these.. An awesome transmitter!

What a beautiful piece of equipment!

Awesome video, thanks for sharing!

this is fascinating - thx for sharing!

The old WFUN in Miami had one of these. I took care of it in 1974 and 1975. And a Gates BC-5B in Tucson before that. Amazing old machines.

Yeah, my Grandfather, now deceased, sold these RCA transmitters. No wonder he was so successful. They don't build them like that anymore!!!

Thank you brings back memories my grandfather use to make power tubes in Paterson NJ his company was called General electronics

I visited this site in 1965 when it was WSAY1370. the studio was upstairs in the house on French Rd. in Brighton NY. the owner, Gordon P Brown, had built the station in 1936 when it was one of 3 existing am's licenced to Rochester (the others being WHAM 1180 and WHEC 1460.) I believe it started at 1210 pre-NARBA. it originally was well-staffed but following an announcer strike, Brown operated it on the cheap as a combo operation... as of 1966, they ran Bell home tape recorders rather than cart machines.

Hmmm Negative peaks higher than positive peaks means you got the audio phase going into that thing backwards also many of those old mercury vapor rectifiers were replaced with Xenon gas filled more modern replacements that were not nearly as prone to Arc back. Finding parts for the Harris MW5 PDM transmitter would be a challenge and I imagine a chore to maintain, glad you guys made the decision to keep the old RCA as a back-up.

Watched this earlier today, thanks for showing on video. Hopefully we'll get more transmitter and radio tours in the future.

This is both fascinating and scary with the voltages involved

A few years ago, I was working on a line at the KDKA AM transmitter site. The original 50kW transmitter looked like this RCA and was still on site (I believe the site guy said it was being maintained as a back-up) and they were operating a new solid state 50kW Harris Transmitter for their main.

Very cool video, thank you so much for sharing this 🫶

A little about selenium rectifiers. I once owned one that was rated 250 V at some tens of milliamperes. Needless to say, I eventually wanted to see, " what it had had for breakfast". Actually nothin very exciting -- definitely less than an alarm clock internals... However, the alarm clock internals never smelled like the eventually blown selenium rectifier! Later on, I was in a job, where I got many more smell incidents. There we used stacks of much larger selenium plates as over voltage clamps, something similar as present MOVs (metal oxide varistors). We bought the plates in quantity and assembled the stacks ourselves. Each plate was good for about 30V. But as said, occasionally some strong spike exceeded the voltage and avalanche current at some plate, shorting it and then the voltage on the remaining plates increased and the failures propagated through the entire stack. The smell provided an easy trouble shooting. You knew what had happened instantly at entering the room, or often even outside.

My stepfather Thomas Franken, was the audio engineer for Ebbets Field,City Field And also a transmitter repairman maintainer. He knew a lot of stuff and he traveled with the Dodgers Just in case they needed him. He had breakfast while he was traveling to St Louis with Jackie Robinson!! So he had a good life! A baseball life!

Thank you so much for giving us a tour! What a fantastic piece of equipment.

Fascinating. Thank you.

Awesome vid. Loved the reference to Photonic Induction too

It's fun to imagine you training a new employee while laughing at every part as you explain how the system works.

Very interesting this is still working after all that time

Nice to see the old girl making RF. I worked on a 10KW predecessor- BTA-10F. I never liked the sliding doors on this model. Thanks for the tour!

Nice tour!

You´re such a nerd, I love the chirp-i-chirp, that thing is very cool. I very much enjoyed the tour, I hope You keep Your job, they are lucky to have You nerd at this place. In Germany am is dead. As a kid in the 70´s it was awsome, sooo much going on on am and shortwave. Even some number stations. Now it´s clear what they were but then they were just strange to me. I love radio. Have a nice day!

2nd time I posted. She's a beauty from the past. Thanks for posting!

Great demo ! No Digi-Key, Mouser, Web, SPICE, CADENCE, microprocessors, FPGAs, or LDMOS FETS yet engineers of yesteryear had a good handle on physics and materials. They were quite innovative and resourceful and produced excellent performing equipment. I have a 60 year old Collins 20V-3 1KW transmitter I've converted for ham use. Except for a rusted 6SJ7, it hasn't skipped a beat. Given their performance and reliability, these old transmitters are indeed engineering marvels. Keep that baby on the air !

Thanks, Nick.

Vacuum tubes rock! Thanks for sharing.

Thanks for posting this. You did a nice job showing this old beauty.

thanks for the walk around , wonderful to see what is a piece of history and still used as a back ,

amazing and that low background hum in most of the video - sounds like the hum the Classic Dr Who Tardis lol

WoW, one very nice system.

love these old units, the first station i worked at WHVW in Hyde Park NY, had an old Collins as a backup and every once in a while we'd through it on the air for a day, just to get the bugs out of it, it was so cool to watch those old audio tubes glowing to music,, it was awesome

The Nautel is stress free. The RCA not so much. My husband's dad was a station GM. What they went through with tubes, rebuilt tubes and lightning. Also their 1964 era RCA could not modulate much beyond 84%. The Nautel would be a different story in so many ways beginning with the cabinet size. I have deepest respect for both transmitters, RCA equals our history and the Nautel the future. What I truly love is GATES Boards and if I owned a station I'd use remanufactured ones in the control & production rooms.

Having never worked AM, the closest I ever came to tube transmission was working at a Class A FM with a Collins 830-E backup running at 3.3 kW. Not nearly as sexy as one of these old RCAs (or even a Continental, for that matter), although the site was operationally unique in that it was the first hydro-powered commercial FM in the US! When we were running on hydro you could watch the power meters fluctuate slowly with the flow of the water through the turbine...

I am taking a look at this now and this basically answers a number of the questions I have had about the transmitter. Having a tube transmitter is a viable backup is not the most common thing anymore.

OH I thought that broadcasters wanted the over-mod light blinking more!! GR8 video

I'm surprised the Hg vapor tubes weren't replaced with generic plugin solid state rectifier units. The time for mercury to vaporize was 5-15 minutes, whereas the glass or finned metal power triodes and tetrodes was only in the one to five minute range. The PSM (progressive series modulation) in the Harris MW series eliminated the modulation transformers and their artifacts, though the newer series digital AM transmitters using banks of power MOSFETs are even more efficient and use more reliable components. Digital transmitters skip the entire idea of A3 modulation, and merely generate a digital analog of a modulated waveform, and switch power at a clock multiplier of carrier frequency, and then filter artifacts. A 5 kW nominal transmitter would likely have a 50 kW peak capacity, to cover 5400 watts carrier power into a directional array phasor, plus some reserve capacity, and to handle 125% or more peak positive modulation envelope instantaneous power needs. Overall (line to load) AC efficiency is around 30-35% on those old tube beasts, around 50% for an MW series Harris, and around 65% on newer digital transmitters (the Nautel among those), which pays for the entire newer transmitter with a bonus of better audio quality over its lifetime. FWIW, I'm a semi-retired broadcast engineering consultant.

Beautiful!

That was awesome!

Blast from the past. Good explanation.

thank you pretty good show .

Great Demo! Not everyone understands that generating RF takes enormous power!

You guys should operate it for Christmas or special seasonal programs, just for that 'ol sound!

EXCELLENT... Love the glassware 👉💎👈👉🇬🇧👈❗❗❗

Ainda vi componentes gigantescos desses em funcionamento na RARET...Portugal parabéns pela demonstração

On a ship I served on the gyroscope, 1939 vintage had tubes 2 to check to make sure the were glowing blue.

fascinating transmitter, never knew that mercury vapour were used on broadcast transmitters, i understand that with some mercury vapour rectifiers need to arc for start up and emitt a beutiful glow.

Sehr interessanter Film - gute Erläuterungen.

This was great!

very interesting. Well, I worked with a 1942 RCA 5E, back in the late '50s. great equipment !!!

That was amazing