BC 375 world war II transmitter used in B17 flying fortresses

This is the famous BC-375 WWII transmitter. This transmitter was used during WWII in the B17 flying fortresses, like the "Memphis Belle". The design stems from the early 1930s, according to the "KISS" concept; keep it simple then there is less that can go wrong. Collins tried to replace it with the much more complicated ART-13 transmitter, but the BC-375 remained in use during WWII despite its obsolescence already then. The reason is because their phenomenal reliability; had I been a soldier flying in the B17, I would have wanted the BC-375 as my main line of communication to the base, not the ART-13 with all its moving parts that can fail. In fact, this BC-375 transmitter was used all the way into the late sixties by many armies around the world. The transmitter was designed for amplitude modulation as well as CW. It gives off about 70 to 80 watt carrier (about 250 watts PEP when fully modulated). The transmitter is of the "MOPA" design, being a main oscillator (using a 211 power triode tube) followed by a single PA stage (also a 211 tube). The PA is then amplitude (plate) modulated using a push-pull amplifier using the same 211 (VT4C) tubes. The video shows the transmitter in full AM operation. I also show how to neutralize the PA when TU units are used that have different serial numbers than the actual transmitter.

[@indy197905]

My grandpa was a radio operator on a B-17. Wish he was alive to see this. I listened to this video on an old cannonball headset.

[@LifeIsTooShortForQRP]

Hats off for your grandfather. Thanks to people like him we now live in freedom.

[@frankhughes_vk6fh]

Great video, envious of all your collection, thanks for sharing.

[@samiam5557]

Wow, a working piece of history! Thanks for sharing with the world.

[@TerryMcKean]

Those sets are definitely awesome...the BC-375... I love that old stuff. Thanks for sharing! :-)

[@D1G1taLKat]

Great video. I would have liked to a see CW demo but still a fantastic demo. I believe this was the transmitter in the bombers paired with the BC-348 I. The early part of the war and eventually replaced with the ART-13. I have a BC-348-R. It’s a single conversion with 2 RF staged before the mixer and 3 IF stages after the mixer at a freq of 915 for the IF. The CW key used in the bombers with this transmitter was the J-5-A flame proof and I have one in absolute mint condition. 73!!

[@AB1Vampire]

Wonderful video, thank you for posting.

[@fourfortyroadrunner6701]

THANK you for explaining the relationship of low RF current vs 50 ohms. I learned this about 1966 from a retired bird Colonel at our local ham club with the club's TCS-12. One of the "other kids" loved to flop meters, and would improperly tune the station balanced line tuner such that the TCS displayed high RF current into the 50 ohm link cable. 375 is one I've never gotten to play with. ARC-5, TCS-12, ART-13, and AN-ARC-2 were some I got to get my hands into, along with the odd VHF FM "tank" radio SCR-508 or similar, along with several Command receivers, and BC-34X series (348), and some others while at Treasure Island ham club, SF, ET-A school--68--69, at K6NCG Look that up

[@justicelut]

Thank you for uploading. Very interesting!

[@scottgs123]

Excellent video! Very well done. Thank you!

[@fourfortyroadrunner6701]

THANK YOU for explaining the RF ammeter. As an old ham (75) who encountered such things as TCS12 when young, I once had a friend who LOVED banging meters. Our local retired bird Colonel explained to him (somewhat impatiently) more than once how to properly set up the link -to - balanced tuner to provide a low Z match to the TCS A note to you youngsters: It is not that difficult to burn out the thermocouple unit in these which is the secret to making them work. Some meters use an external thermocouple, as well, so if you find a meter, do not assume that it's scale equates to the meter per se.

[@W4AX]

I am about to place my NOS BC-375 on the air. The BC-375 is still in the crate from the factory as are all tuning units. Thank you for an excellent video and especially on how you neutralized the PA. I probably would not have thought to listen to the signal in FM mode. Great tech tip! Thanks again!

[@ericrawson2909]

I saw one of these in the Kodiak military history museum. It is a shame I didn't have more time there. They have a lot of restored equipment, and I loved the fully functional teletype. Well worth a visit if ever you get to that remote island.

[@joshjosh6526]

Very cool! I have three of the tuning units for one of those, but no transmitter... yet! Surplus radio gear is awesome! Thanks for sharing!

[@clintonandrews1538]

During WWII Detroit Ch. 4 weather forecaster Sonny Eliot was a pilot on a B-24 bomber. During flights at high altitude in an unheated unpressurized aircraft, (temperature -12ºF at 20,000 Ft; -30ºF at 25,000 Ft) moisture from the breath would cause carbon microphones to literally freeze solid and quit working. So before taking off, the air crews would enclose their mics in a condom to shield it from moisture. When Sonny Eliot's B-24 got shot down over Germany he and the rest of the crew were arrested. As the German officer went through the pockets of Sonny's uniform, he came across a number of condoms. The German officer remarked "You vill not need zees vere you are going." Twenty years later Sonny was still laughing about it.

[@tommygun32917]

That is a really cool piece of history 👍

[@roddale8412]

Wow, a WW2 B17 radio with valves. This is awesomeness beyond awesomeness.

[@tpobrienjr]

Excellent demo and explanation!

[@rádiosantigos1958]

Very nice explanation. Congrats!

[@heipuntnl]

Thanks for sharing! We had one for medium wave pirate radio in the 7 ties! Worked well. One tube is in my display cabinet ( memory lane :-) ) .

[@LifeIsTooShortForQRP]

Ik ga de band weer verlaat'n, Nog even een tikkie van de schijf met de knop een halve kwart los 🙂 Dat waren nog eens tijden...

[@maninthevan53]

wow thanks for a look in the past , very nice p

[@nickaxe771]

What a lovely bit of kit....must have cost a bomb in its day.....sad to think what happened to most of them. Thank you Sir for show yours to us and explaining it. The Collins ART-13 is also a stunning bit of kit.....as fitted to the B29 I believe.

[@davidhunt3161]

Thanks good video

[@johnmarlin4661]

De K6UAE/7 Thanks for the excellent video and talk . I at one time had an ARC5 rig on 40 meters LOL

[@nunyabizness199]

Excellent ! I love boat anchors... It's really good to see this running. I had one until my x wife thought it would be a great idea to get rid of it for me back in the late 90s. I managed to save my BC 348K.

[@LifeIsTooShortForQRP]

The way to deal with that situation: Get rid of the wife first.

[@nunyabizness199]

@@LifeIsTooShortForQRP Right right...

[@MrBugsier5]

@@LifeIsTooShortForQRP correct answer! lol

[@ruslannabioullin3664]

@@LifeIsTooShortForQRP Find a proper wife...

[@gordonwelcher9598]

This is a beautiful transmitter, I wish I had one. The modulation sounds really great. I would like to install one in my rolling fortress minivan. I am sure I could get 150 watts with a bit of modification and a decent B+. I have run a 211 at 1700 volts in special ICAS++ mode. Maybe too much for plate modulation. They cost $2.99 at the time.

[@LifeIsTooShortForQRP]

Yes, I remember that. Surplus stores used to sell four of these tubes in their original military spare case for peanuts. And no one was interested because they were considered obsolete tubes for ham transmitters, difficult to tame and not working great above 10 MHz. And now, an single US-made 211 tube from General Electric goes for an amount way north of 200 dollars.... Madness.

[@gordonwelcher9598]

@@LifeIsTooShortForQRP I bought one around 1976 at Etco Electronics in Montreal Canada for $2.99. A friend of mine tried to get two of them working in push pull at about 30 megahertz, he could not get the neutralizing right. The amplification factor is too low to work well in grounded grid. I should have bought more for audio use. They had many of them. I must finish working on my time machine.

[@jacquesantigny4961]

Hi thanks for your video, currently I restore the same transmitter based in france.

[@comethk1]

jacques Antigny a

[@LifeIsTooShortForQRP]

I would love to have the French made version - they were the nicest ones one could buy. Remember Den Hollander in Haarlem selling those French ones unused in their original crate, for less than $50. Those were the good old days.

[@hanz090]

Hi please can someone tell me what a m6 director is ? I have a part from one packaged in 1944 And never opened so I don't know what part it is. It's made by delco I think .any help would be appreciated

[@SA2CLC]

Thanks for sharing. Something about those wrinkle painted cabinets :)

[@nunyabizness199]

Yes indeed, you have to bake them in the oven to look like that ☺

[@Stelios.Posantzis]

I agree with the statement that transmitter tubes belong, well, in transmitters foremost, especially the rarer ones The same holds for all sorts of other rare radio tubes used in receivers that somehow find their way to audio amplifiers through the evil means of marketing. Magic eye tubes are a case in point: they have no business whatsoever in an audio amp, however, some manufacturers -whose products are just as much about the looks as they are about the sound reproduction- flout on them on their shiny new toys. Unfortunately, a lot of high end audio amplifiers these days seem to fill some kind of existential void in some peoples' eyes. They mostly achieve that through visual artifacts and bold statements about rare and expensive materials used in their construction -which is always by hand and takes a few hundreds or thousands of hours of course. In the audiophile's defense though: a) transmitter triodes are the most linear electronic amplifier devices and reputable tube manufacturers are simply reluctant to take up their manufacture: the narrow market does not justify the cost outlay nor the production cost b) it is not the audiophiles' fault that these transmitters (and many other such devices) were junked by the skipful upon being decommissioned and those that were not, were sold for peanuts at hamfests or the ham radio circuit -if not just given away. The audiophile always seeks the cheapest, fastest way to audio nirvana and if a decommissioned thoriated tungsten triode fits the bill, then so be it. c) audiophiles have had historically to put up with hyperinflated prices for many a time substandard gear and were always given limited choice with respect to amplifying devices (the lack of a standardized 50W or 100W power audio triode is, I think, a case in point: RF engineers otoh have a wealth of choices). d) were it not for the surge in tube demand created by audiophiles (and guitarists) there would be no receiver/audio tube industry to speak of today -heck every piece of gear needed to manufacture tubes ever again would have been scrapped long ago and the operational knowledge would have been lost with them forever. Technologically, audiophiles and ham radio fans are after the same thing. Tube manufacturers aim to sell to both (and to guitar players). What is missing from the equation, I dare suggest, is historical tube equipment preservation societies to further the cause for old electronic equipment. They could play a role in safeguarding stockpiles and commissioning new production runs for rare components. The same problem is faced for example by owners of old scopes and other precision instruments etc.

[@towerman75]

About 5 years ago, a ham in Florida had a BC-375 and all matching TU units. I bought it, and when my Son brought it to the QTH, never in a million years, would I have believed the condition the unit and all it TU's were in. It was as though it had been in storage and never used in the war. As a matter of fact, I unboxed the Tu's from their WWII boxes, still in the waxed paper they used at the time. I was beside myself, like a kid in a candy store. The only think missing, was of course the PA's ( as you said, some audio idiot ). Searching on the internet, I was able to find them on E-Bay, and at the time, they were better than $ 200.00 each. Being on Social Security, I couldn't afford them, so the unit sat in my radio room for about two years. It killed me to have to look at them each day. Through time, I ran across another Amateur looking for a BC-375. He made the right offer, and I sold it. He didn't need the TU's, so I still have them. I think there is a total of seven units. The reason for leaving this note to you, is that you may be interested in them, if so, just let me know. I do U-Tube at random, so it is possible to miss your return answer, so here is my E-Mail address: [e-mail] Hope to hear from you. Jim WA5WRE

[@LifeIsTooShortForQRP]

Jim, I already have all TU units for the BC-375 here, so I have to pass, sorry. But I will leave your offer up here, I'm sure there are plenty of other collectors who would like to buy them from you. Yes you are correct, the 211 tubes (VT4C) are difficult to find. I was lucky to buy 4 of them for $50 each on eBay a while ago, from China. They work perfect in the BC-375, they are an exact copy. But nowadays the Chinese offerings for the 211 tube have become scarce I noticed. The cheapest I could find is for $85 per tube (plus $12 shipping), not cheap but if one wants to get the transmitter running it seems to be the lowest cost option. The original GE tubes now go for $1000 each when unused, which is complete madness of course. Here is the Chinese seller I found: www.ebay.com/itm/165449037748

[@gordonwelcher9598]

I remember Etco Electronics in Montreal Canada had surplus GE 211 NOS for $2.99 in 1974. I bought only one to test. They did not work very well as RF power amplifiers at 30 megahertz so I didn't buy any more. Not good for grounded grid and I was unsuccessful trying to neutralise them. The 813 worked much better, I finally found some used for $10 each at Standard Electronics also in Montreal. They worked very well, 2 in parallel gave about 600 watts. Very easy to drive. I wish I could go back and buy all the 211's, they had a lot.

[@MrGordonFreeeman]

+1 Great video

[@MrBugsier5]

Are you sure on the antenna amp meter? going in to 50 ohms should give higer amps, than 250 ohms of the wire antenna.....is it the right amp meter???

[@HD7100]

I had to laugh at your KZbin name. I agree but the best I can do with my two vintage AM transmitters is 35 watts out. Oh- that transmitter is just great!

[@paullee983]

I picked up a us navy transmitter at a local antique shop. Having trouble finding information on it, it's in a wood crate, labeled as ATM-1 Transmitter, looks brand new as all extra parts/tube station are still wraped in paper. May be a meteorological unit. It has a wind cup (3 cups) looks to to be portable to deploy from ship or shore. I was going to donate it to a navy muesum at great lakes navel station. Any thoughts, thanks. Paul

[@brianfrommaumee]

Another outstanding video! Just curious - how much do all the components weigh? That looks like a lot of radio weight to load up in an aircraft.

[@LifeIsTooShortForQRP]

The transmitter weighs around 55 Lb. In the B17 flying fortress, it was used with a rotary inverter called a "dynamotor" (not shown in the video) which converted the 28V aircraft voltage to 1000V (needed to supply the transmitter plate voltages) That dynamotor alone weighs 39 Lb. Sounds high, but keep in mind a single bomb was 500 pound and the plane was carrying many of those. So in the grand scheme of things the weight of the radio equipment was insignificant. If you want to see more detail, you can download the equipment manual here: w5jgv.com/downloads/BC-375-E.pdf

[@wa9kzy326]

Your knowledge of this classic transmitter is most impressive. If memory serves, all aircraft radio operators were military officers, not enlisted men, who were specially trained to keep this transmitter in tune, at all times.Anybody know how long the military training school lasted for?So much basic knowledge has been lost by going to auto tuners. .Thanks for sharing.

[@LifeIsTooShortForQRP]

Appreciate the kind words!

[@ronalddaub7965]

I have a garod ship Crystal Monitor and calibrator it has the antenna and phones and two tubes I believe it just calibrate and I was wondering if it monitored it goes from approximately 26 to 28 megahertz 11 different settings I know it has some crystals and tubes in it and it's for the Navy and Marinesww2

[@nicoschadjidemetriou4373]

Is given to me many years ago an old aircrafts TRANSCEIVER smaller full of valves, having 16 VHF Channels . It has no panel. It's remotely controlled,. Its look that is 5-10 Watts. It is using 24-28 volt DC. The dynamo-motor makes noise like a vacuum cleaner and also sucks air for cooling all the inside and also filters the air . I fancy this noise. I painted the cover .

[@LifeIsTooShortForQRP]

Maybe a British TR1934 VHF aircraft transceiver? www.marktplaats.nl/v/verzamelen/militaria-algemeen/m1931049585-tr1934-tranceiver

[@rsattahip]

Wish the government was still limited to technology like that.

[@Inkling777]

In my early ham days I used command sets for 80 and 40. I assumed they were for talking back to England and was surprised that they were for plane-to-plane communication inside a squadron. I assume, given its greater power and trailing antenna, this one is how B-17s talked back to England.

[@LifeIsTooShortForQRP]

Your initial assumption is correct, these were used for long range comms back to base, not for communication between planes, they used VHF for that. But these BC-375 transmitters were almost always used in carrier-CW mode, using very short transmissions. The amplitude modulation mode was almost never used. In fact, many B-17 radio operators (when running out of spares) would pull one of the VT-4C tubes from the push-pull plate modulator if the transmitter PA or oscillator tube went bad, since AM was not used anyway.

[@janvisser8452]

Rare video. But it is not complete ! What are the things for behind the tubes ? And can you show us behind the back please ? And also ofcourse in the drawers. Not to forget the ant tunerpart which is a piece of art. A lot of these models were on the Dutch dump market. Please show and tell.

[@TerryMcKean]

Definitely... it'd be cool to see the other side, with the modulation xfmr and other cool things and ingredients to that 'mitter. :-)

[@LifeIsTooShortForQRP]

They are the bias current settings for the tubes as well as the microphone gain potentiometer. The terminal strip you see at the top-back (the one with the jumpers) is to set the filament voltage at the correct point for a given input voltage (either 24V or 28V). The video would have gotten too long had I added that as well, sorry

[@douro20]

How many power supplies does this have? There is an old radiotelephone set at one of the local antique malls...I think it is a French one if I'm not mistaken...

[@LifeIsTooShortForQRP]

Sounds like it might be a French BC-1000, or maybe an AN/GRC-9 radio. Google these and compare with the one you saw.

[@scharkalvin]

Those 211 tubes are highly sought after by audiophools today, they sell on ebay for a few hundred dollars each! Copies are being made by the Chinese for that market. The type 10 is also very expensive. Damn triode audio nuts!

[@LifeIsTooShortForQRP]

I know they are VERY expensive. But the Chinese make pretty good duplicates nowadays, for $50 each (shipped), not too bad. I tested those Chinese tubes in another BC-375 transmitter I am restoring, and they work remarkably well, EXACTLY the same gain and inter-electrode capacitance as the original General Electric USA made 211 tubes. The Chinese brand I tested is "Shuguang", they work very well and have good workmanship. Here is the KZbin video where you can see them in action: kzbin.info/www/bejne/oV7Jnpx6lNuGeqs

[@chrischarters376]

Audio nuts lol. Thanx for sharing 'lifes2short'.

[@scotthansen6468]

I have one of these with all the matching crystal sets. I am looking into getting it up and running and have some questions for you. I do have the dynamo but it’s seized up so I need to come up with an alternative power source also I have no cables. But I would like to make it functional.

[@LifeIsTooShortForQRP]

Hello. This radio did not use crystals and no crystal set exist for it, so that must belong to another SCR radio. Maybe it belongs to a BC-604, a BC-610, a TRC-1 or a BC-659? Make a short video of it then we can tell you. The dynamotor for this transmitter should be not too hard to repair, but I do not recommend trying to get it to work if you are not familiar with WWII equipment. This BC-375 transmitter requires 1000 volts to work (which is what the dynamotor generates), and these kind of voltages can kill you in an instant if you make a mistake. My advice: put the transmitter on display at prominent place in your house, but do not try to make it work. Cheers.

[@scotthansen6468]

Sorry not crystal set but running units. All a matching set.

[@LifeIsTooShortForQRP]

@@scotthansen6468 Got it. Nice buy, to get a BC-375 with the matching TU boxes, that is rare! Cheers.

[@pedromolin6941]

I like...fantastic

[@shoominati23]

Didn't they have like a 20 metre long cable aerial that they trailed out of the rear of the plane when they needed to talk?

[@MrBugsier5]

Jep, they did.

[@shoominati23]

And I bet even over France the base back in england would have been static

[@ronalddaub7965]

Do you know anything about 1950s weather balloon radio s o n d e s? That work on HF. 2 Small electron tubes

[@wa9kzy326]

How did the operators neutralize their transmitters back in the war days?

[@LifeIsTooShortForQRP]

They didn't - it was done in the factory; tuning boxes were matched to a specific transmitter there. The TU boxes were then given the same serial number as the transmitter, for the operators in the field to recognize them as belonging to that transmitter.

[@andrzejoskedra1062]

Hi ! I'm Andy SP9NH, I have simillar transmmiter model BC-191 N mounting in 1957 in North Africa. Have you any web address for User Manual? Best 73 Andy

[@LifeIsTooShortForQRP]

www.radiomanual.info/schemi/Surplus_NATO_BC/BC-191_serv_user_TM11-800_1942.pdf

[@andrzejoskedra1062]

@@LifeIsTooShortForQRP Hi! Many thanks for fast replay on my asking, this will be very usefull for me. My BC-191N is in very good conditions, looks like was never in use! Best greetings, have a nice day -Andy

[@andrzejoskedra1062]

PS- I'm SP9NH, welcome you to see my page on QRZCQ.com my e-mail is [e-mail] I would like to send you a few pictures of my BC-191 N, let me know your callsign or e-mail address, 73, Andy

[@robertporter1429]

Curious what these are worth? My dad pulled one out of a B-17 at Wright Patterson AFB in 1952...It is in very good condition.....I have it now...just curious...thx . Please write me back if you will ... I sure want to learn more about what I have here!!! Thx!!

[@LifeIsTooShortForQRP]

It highly depends on the condition. If it has good paint, clear lettering, no corrosion (also not inside), no damage and all tubes and TU box are present it should easily fetch $500, more likely $700. If the original mounting is still present add another $150. The dynamotor (not shown in this video) is worth another $200 if in good condition. Cheers.

[@robertporter1429]

LifeIsTooShortForQRP Thx for the quick reply. What do you mean by the original mount? And also. Aren’t the tubes inside worth about $250 a piece?? Many thx!

[@LifeIsTooShortForQRP]

@@robertporter1429 This is the shockmount I was talking about: www.worthpoint.com/worthopedia/military-radio-bc-375-shock-mount-1917201004 The tubes could be worth $250 if they would be unused in their original box, which is not the case here of course. Cheers.

[@robertporter1429]

@@LifeIsTooShortForQRP ...thanks so much for your help with this...I sincerely appreciate your input....would luv to send U a photo of my rig...but don't see how to attach an image... on this page....Regards, RP

[@LifeIsTooShortForQRP]

@@robertporter1429 Robert, just make a short video of it and put it on KZbin! You don't necessarily have to have it running for a video. Cheers.

[@nor4277]

Those radio in the movies could pick up am radio stations too right?anyone.please if you no.

[@LifeIsTooShortForQRP]

Yes they could. Even better - planes used AM radio stations as location beacons.

[@nor4277]

@@LifeIsTooShortForQRP thanks for the info ,you have a great part of our history very amazing radios.

[@user-xs9zr9xs4c]

I would have thought high impedance was low current high voltage and vice versa

[@LifeIsTooShortForQRP]

That is correct for antennas that are resonant. When an antenna is not resonant (which is almost always the case for this transmitter in an aircraft having a trailing wire antenna), there can be a large component of current that does not take part in delivering actual radiated power ("out of phase" current, also called "bad SWR"). This is the part of the RF current that the built-in antenna tuner needs to cancel out. But the RF ammeter cannot distinguish between such resonant currents and "blind" currents, and will therefore show a large current going into the (non-resonant) antenna depending on the impedance of the antenna (which on it's turn is frequency dependent). Think of it as the power factor that applies to the AC grid. An inductive load (or capacitive load) will show a large current going in that does actually not dissipate any power in the load. That translates to a power factor of 0, and won't make your outside kWh meter move. A purely resistive load (like an incandescent light bulb) will exhibit a current going in that DOES deliver actual dissipated power, and the power company will charge you for that one. That is a power factor of 1. Anything in between (like an AC motor) will be a load that is partially resistive in combination with a partial inductive (or capacitive) load. It is the same for the antenna that forms the load for this transmitter, but then at a much higher frequencies than 60 Hz. But the concept remains the same.

[@maninthevan53]

o my lord wow lol

[@AnotherFredBloggs]

You forgot to relock the neutralising control

[@AnotherFredBloggs]

.

[@LifeIsTooShortForQRP]

My bad!

[@physicaldetails8492]

FU-5

[@user-cn5kv5ey4c]

Вас слышно в Москве... 💡🙉

[@fourfortyroadrunner6701]

That looks like an awfully small dummy load!!??

[@LifeIsTooShortForQRP]

50 watts continuous. The radio is 70 wats carrier, so if you keep the transmissions short the dummy load can handle it just fine. Cheers.

[@user-mf8hn2zu7j]

Ус-9 имею тоже роман украина