Oh Michael, that was true nostalgia for me. At the age of 6, I "helped" my uncle construct that project in 1955. Although he was coal miner, he had an avid interest in all things electronic and tutored me whenever possible. I had a fascination with his AVO minor which he taught me how to use without destroying it ! Happy days which fired me up and resulted in many enjoyable years of employment, culminating in 30 years of teaching at my local tech college. As late as 1980, thermionic device theory was still on the syllabus for the B/Tech and City and Guilds courses I used to present. I therefore owe a lot the Practical Wireless, and my uncle of course. Many thanks for sharing this with us, best Christmas wishes.
Hi Michael, that took me back in time. I started to take Practical Wireless magazine in 1960 and was so keen on building circuits but not so much wireless. I was building my 1st electric guitar and realised I needed an amplifier so trawling through the pages I found a kit to build a Mullard 510. I saved my pennies and ordered it and I can still remember the smell when I opened the box of parts. So exciting !!! I duly assembled the amp and it provided me with a few years of service until I could afford one with 30 watts. There really isn't anything to touch valves for guitar and again the smell is magic. I wish I had saved all of the copies of that mag as I had it right up to 1966. I then started sn apprentership with the Marconi Company in Chelmsford where I worked for 22 years when they folded. Great times and a great video - Thankyou !!!
I am a goof. When you mentioned the daughter and the grandkids asleep downstairs, I turned down the volume and kept it quiet in here. For a video I am watching. Recorded earlier. 4690 miles away.
In 1962 as a 15 year old I built a HAC (Hear All Continents)radio from a kit. It had two valves and I remember the thrill of seeing the valves glowing in the dark when I had gone to bed and was listening to it in the dark. Something very special about a lit valve.
Brilliant project. My dad's friend gave me a lot of vintage stuff. I remember dumping hundreds of old PW and PE magazines by F.J. Camm, years later. Probably worth a bob or two now, but I needed the space. I wonder what other gems I lost over the years. I remember he gave me a power amp that came in two giant metal boxes. I think one of the boxes had 4 KT66 valves and some seriously heavy transformers. I was probably around 10 or 11 years old. The best device was an old dictaphone that recorded onto paper magnetic disks valled a "Recordon." To erase the disc was a hand held bar magnet. Now that one is still in the garage with recordings of Radio Caroline and my long dceased grandad. Must get it working one day... 😳
You did a better job on the cabinet than I could have. Looks great. Growing up in the 70's, I didn't read comics, I read Practical Wireless. LOL. 🎅Merry Christmas Everybody🎅
Great job MD! Enjoyed your articles in Practical Television (along with the rest of its content), the anticipation of a new magazine, sadly missed now, was a highlight of the month. Thank you for continuing to deliver and share your great content on TH-cam! Merry Christmas and Happy New Year to you and your family!
Nice project Michael and love the nostalgia, especially that copy of PW from 1955. I think you managed to get a very genuine 1950s look with that cabinet! A very merry Xmas to you.
Another great video Michael. Thank you so much. Merry Christmas ans continued success in 2025. You sir are an absolute legend..I've been a follower since your articles in practical television
I had a subscription for Practical Wireless from being 12 years old. I'm 72 now! I used to read it from cover to cover. Anyone remember the Sinclair kits? Oh, and the army surplus. I bought a 31 set, and took out the BBC TV 6pm news for the whole of my village! I was soon informed of my mistake, by violent hammering on our door! Happy days!
Bringing life to a handful of components always makes me smile - Nice job MD. have a great Christmas and if you're down in South Somerset next year, pop in for a cuppa and a workshop tour. All the best MJ
Great video. Liked the silent bits. If you listen to some creators now, they will say 'What are we gonna do in this video, well in this video, what we are going to do is we are gonna...' Too many words saying nought. Sorry to hear about your talented friend, I think I might know him. Re the sawing, I am happy to pop up and show you how to do it really easily, take about 15 mins, failing that, if you want to send me specs of anything in the future, I can soon knock things up.
Graham wasn't realley my friend as such, more or a customer but I have known him for well over 40 years, he was always coming into the shop I worked as a kid buying tools. Re the wood, I can't belive I made such a good job with a hand saw, I think someone's looking over me.
The coil was a lucky chance buy, I saw a load of radio coils adverized on e Bay, most of it crap and I could see what appeared to have part of the correct number on so I tool a chance!
What a lovely result. Most of my kits didn't look like the original. They ended up in ice cream containers and the like. Presentation was not important when I was a kid. My dad would sometimes build a case if he had time. As I get older, I've been considering mentoring some younger children in electronic projects to keep the hobby alive. I'll see if I get enough time. Just got back into audio repairs and it's busy.
Great job Michael. Makes me want to try it myself - but I'm a little busy right now. If you remember, earlier this year you went to J. Birkett's in Lincoln and filmed the inside of the shop of vintage electronics and various aeroplane instruments. I decided to visit that shop and bought a Marconi R1155 "Lancaster Bomber" receiver. Well I'm currently deep into its repair, checking resistor values, replacing crumbling wires etc. Not going to be finished for Christmas next year at the rate I'm going at (especially as I've decided to reconstruct the DF circuit), but an enjoyable project none the less. Wishing you and your family a Merry Christmas and a very happy New Year!
Case looks very good Michael - well done - nice project overall, thanks for posting. Best wishes for Christmas and new year and looking for ward to the next video!
Must be a trade issue with cutting wood straight as a now retired TV engineer I can’t either. I was OK with Fablon at Radio Rentals when we used to re-cover the teak cabinets in black. Great project Michael and have a great Christmas
I worked for the BBC on transmitters from the early 1960s. EF50s were used for a lot of RF low power units and they rarely needed replacing even running 24/7 for years. Well done Michael even if you mistook the suppressor grid for the screen grid!
Sorry Michael, that appears to be the suppressor grid, the screens are up to HT+ and resulting HT on the kathode, suppressor grids are normally tied to the kathode or ground but can be used as secondary control grids. Keep up the good work, love your videos.
The EF50 probably the most important valve during the WW2 made by Philips in the Netherlands. The basic valve for most radar sets display system. I suspect that is why they were used in the circuit as they were very cheap and plentiful.
While the Philips factory at Eindhoven was under Nazi occuption from 1940, EF50s were made by Mullard in England. Later Sylvania in the USA produced vast numbers of them.
The first time I had ever seen a EF50 was at tech collage on a very old, even then, TV that seemed to have dozens of EF50s in every stage except those needing power valves. The big red can made them look lifeless as you could not see inside, not even the heaters.
Hi, Michael. "Jack Armstrong" here of "Television" magazine fame. I built at least one superhet valve radio in my teens. In fact I blew my Dad up with it: I fitted the reservoir capacitor the wrong way round! Anyway, your plywood cabinet looks just fine to me. Ideally, the plywood needs to be cut with a saw bench, using a fine tooth circular saw but you did OK. Merry Christmas, my friend.
What a shame we can’t hear the Light Programme again or the Goons show or Cltheroe Kid… I have a 1952 Bush valve set but all those wonderful old radio broadcasts are silent now.. I can think back as a child in the 1960’s sitting with my Nan listening to family favourites, it’s so sad we have lost all that
Well done Michael! Nothing like a nostalgic project for the holiday season. Many years ago I built a converter that received aircraft frequency broadcasts, 108-136Mkz, and rebroadcasted them on an AM 650-1700 Khz frequencies. I also built a Knight Kit oscilloscope kit, sold by Allied Radio in Chicago, when I was in high school, arounf 1965. I still have it and it still works. Question: I'm not familiar with the reaction control, what is that for? A gain control?
Have yall heard of BRUCE ROSENBLIT He has made Transcendent audio with very very well designed amplifiers, There is a 300b that can use rectified mains, and no output transformer and only 1 gain stage, 4 300bs in parallel. Absolutely right on. The schematic is in a very informative book Tubes and Circuits. Hes the one that makes sense, out of all the other recirculations of circuits, this guy explains it without confusion or obfiscation.
dont know if i have that particular issue, but i do have a load from late 50s to late 60s, most with the original free 'blueprints' in the ones that had them, but i have that circuit in a 'practical wireless circuits' book, always wondered how well or not that circuit would work! i have a radio that was 'home built', using 3 EF50s, but a more 'normal' circuit, i think from a 'wireless world' magazing doesnt work very well , plus another home built one. in style of a wood cased pilot major maestro, normal superhet, and works fairly well, and yet another one with a unique style case, also superhet, doest work too well !
I am exactly the same with wood, can never get a good result! Metal, no problem! I have that issue of WW, interesting. Impressed that you had the metal rectifier! So, come on, own up, did it work first time?
Yes it did work first time due to the ready made coil, but for safety I did power it first from a bench power supply just to make sure there was nothing amiss.
wonder how later valves such as EF91s, EF80s, or even high gain frame grid types EF184s would work? EF91s were certainly used a fair bit for home built stuff maybe a EF184 first valve feeding a PL84 output, for a bit more oomph, PY82 rectifier , and a nice big hot dropper resistor 😉 live chassis, of course, but class Y2 isolator cap for the aerial..??!!
Crikey! G3 is not the screen grid. The volume pot is wirewound because it's across the OPT secondary, not because of the miniscule V1 cathode current. Nice build though in spite of the schoolboy errors
You are of course correct because I was pointing to the wrong valve G3 is the suppressor grid, it's valve 1 where the screen grid is returned to cathode potential. A slight mistake in my un edited video.
What you are calling the screen grid is actually the suppressor grid, the screen grid is returned to HT, perfectly normal. It makes no difference using an RF pentode at audio, the limitation is in anode current , not relevant here because of the low volume anyway. The radio is simply a regenerative detector with one audio stage, nothing very suprising at all.
Of course your correct, I should have made reference to the first valve where the screen grid is returned to cathode, little mistakes always creep into my videos as there completely un edited now.
I made a regenrative radio using two EF50s. The design came from a book "Fun with radio". It was probably a good design but my choice of placement of the components wasn't. Skill was needed when tunig it in, otherwise it screemed somewhat. It picked up Luxembourg on 208 metres really well and then re-transmitted it on long wave!
@michaeldranfield7140 oh, that's different story. I was reading some russian literature on the subject and i saw the same thing. They say that it is some kind of AGC or negative feedback. It makes some sense but I haven't totally understood the principle.
Very weird circuit. TBH, with a few more components you could have had a conventional volume control with coupling capacitors, and an audio output valve with a much lower value cathode resistor. No need to mess around with bias etc. I think the EF50s were chosen because there were plenty of war surplus ones available in 1955. I think your point about negative feedback is hardly relevant considering it is an AM receiver and TRF so plenty of distortion to begin with.
Oh Michael, that was true nostalgia for me. At the age of 6, I "helped" my uncle construct that project in 1955. Although he was coal miner, he had an avid interest in all things electronic and tutored me whenever possible. I had a fascination with his AVO minor which he taught me how to use without destroying it ! Happy days which fired me up and resulted in many enjoyable years of employment, culminating in 30 years of teaching at my local tech college. As late as 1980, thermionic device theory was still on the syllabus for the B/Tech and City and Guilds courses I used to present. I therefore owe a lot the Practical Wireless, and my uncle of course. Many thanks for sharing this with us, best Christmas wishes.
Hi Michael great job works very well Merry Christmas and happy new year thanks for all videos all the best from Peter 😀🏴
Hi Michael, that took me back in time. I started to take Practical Wireless magazine in 1960 and was so keen on building circuits but not so much wireless. I was building my 1st electric guitar and realised I needed an amplifier so trawling through the pages I found a kit to build a Mullard 510. I saved my pennies and ordered it and I can still remember the smell when I opened the box of parts. So exciting !!! I duly assembled the amp and it provided me with a few years of service until I could afford one with 30 watts. There really isn't anything to touch valves for guitar and again the smell is magic. I wish I had saved all of the copies of that mag as I had it right up to 1966.
I then started sn apprentership with the Marconi Company in Chelmsford where I worked for 22 years when they folded. Great times and a great video - Thankyou !!!
I am a goof. When you mentioned the daughter and the grandkids asleep downstairs, I turned down the volume and kept it quiet in here.
For a video I am watching. Recorded earlier. 4690 miles away.
In 1962 as a 15 year old I built a HAC (Hear All Continents)radio from a kit. It had two valves and I remember the thrill of seeing the valves glowing in the dark when I had gone to bed and was listening to it in the dark. Something very special about a lit valve.
Thank you Michael. I really enjoyed watching you completing that Practical Wireless project. What a great job you made of it.
Brilliant project. My dad's friend gave me a lot of vintage stuff. I remember dumping hundreds of old PW and PE magazines by F.J. Camm, years later. Probably worth a bob or two now, but I needed the space. I wonder what other gems I lost over the years. I remember he gave me a power amp that came in two giant metal boxes. I think one of the boxes had 4 KT66 valves and some seriously heavy transformers. I was probably around 10 or 11 years old. The best device was an old dictaphone that recorded onto paper magnetic disks valled a "Recordon." To erase the disc was a hand held bar magnet. Now that one is still in the garage with recordings of Radio Caroline and my long dceased grandad. Must get it working one day... 😳
You did a better job on the cabinet than I could have. Looks great. Growing up in the 70's, I didn't read comics, I read Practical Wireless. LOL.
🎅Merry Christmas Everybody🎅
Excellent job, thank you for bringing 1955 back to life... Merry Christmas
Great job MD! Enjoyed your articles in Practical Television (along with the rest of its content), the anticipation of a new magazine, sadly missed now, was a highlight of the month. Thank you for continuing to deliver and share your great content on TH-cam! Merry Christmas and Happy New Year to you and your family!
very nice, (especially the cabinet) happy Christmas to you and yours
Excellent work Michael and good work the cabinet well done it looks Wonderful,Ian from Australia,
Nice project Michael and love the nostalgia, especially that copy of PW from 1955. I think you managed to get a very genuine 1950s look with that cabinet!
A very merry Xmas to you.
Excellent job and you cut wood with precision,spot on 👍
Another great video Michael. Thank you so much. Merry Christmas ans continued success in 2025. You sir are an absolute legend..I've been a follower since your articles in practical television
Many thanks for that
Splendid. Well done Michael.
Can't belive I made such a good job of cutting the wood, I think someone's looking over me.
I can't say much for the weird circuit but the dad gum thing plays! That's what counts! Good job! Merry Christmas to you!
Thank you for that, we both have a similar interest in valves, the only thing is I can't make mine like you do!!!
I had a subscription for Practical Wireless from being 12 years old. I'm 72 now! I used to read it from cover to cover. Anyone remember the Sinclair kits? Oh, and the army surplus. I bought a 31 set, and took out the BBC TV 6pm news for the whole of my village! I was soon informed of my mistake, by violent hammering on our door! Happy days!
I have loads of sinclair stuff.
Awesome ! Merry Christmas to you and yours !
Bringing life to a handful of components always makes me smile - Nice job MD. have a great Christmas and if you're down in South Somerset next year, pop in for a cuppa and a workshop tour. All the best MJ
Sadly we don't go away too far now we have two small children in the house as well.
Thanks for sharing that, a great project.
Great video. Liked the silent bits. If you listen to some creators now, they will say 'What are we gonna do in this video, well in this video, what we are going to do is we are gonna...' Too many words saying nought. Sorry to hear about your talented friend, I think I might know him. Re the sawing, I am happy to pop up and show you how to do it really easily, take about 15 mins, failing that, if you want to send me specs of anything in the future, I can soon knock things up.
Graham wasn't realley my friend as such, more or a customer but I have known him for well over 40 years, he was always coming into the shop I worked as a kid buying tools. Re the wood, I can't belive I made such a good job with a hand saw, I think someone's looking over me.
Another great one. Merry Christmas and Happy New year to you and yours.
That's a great fun project you've built there, Michael. My only snag would be obtaining the coil.
All the best to you over Christmas,
Richard
The coil was a lucky chance buy, I saw a load of radio coils adverized on e Bay, most of it crap and I could see what appeared to have part of the correct number on so I tool a chance!
A really enjoyable video Thanks. Happy Christmas Michael.🎄
What a lovely result. Most of my kits didn't look like the original. They ended up in ice cream containers and the like. Presentation was not important when I was a kid. My dad would sometimes build a case if he had time. As I get older, I've been considering mentoring some younger children in electronic projects to keep the hobby alive. I'll see if I get enough time. Just got back into audio repairs and it's busy.
vary nice job. well done. happy xmas.
thank you Michael a great video and what a great Project to pick , and great cabinet work Merry Christmas 🎉
Brilliant job. Looks very much the part.
Many thanks for that.
Thanks for the video Michael, I was born in the late 50’s so grew up with valves and transistors… best wishes to you and your family for Christmas.
Great job Michael. Makes me want to try it myself - but I'm a little busy right now. If you remember, earlier this year you went to J. Birkett's in Lincoln and filmed the inside of the shop of vintage electronics and various aeroplane instruments. I decided to visit that shop and bought a Marconi R1155 "Lancaster Bomber" receiver. Well I'm currently deep into its repair, checking resistor values, replacing crumbling wires etc. Not going to be finished for Christmas next year at the rate I'm going at (especially as I've decided to reconstruct the DF circuit), but an enjoyable project none the less. Wishing you and your family a Merry Christmas and a very happy New Year!
Thanks for taking the time fella stay lucky, stay safe, and a merry Christmas to you and your family!😉🎉
Many thanks for that
Case looks very good Michael - well done - nice project overall, thanks for posting. Best wishes for Christmas and new year and looking for ward to the next video!
Well done sir. I love the older tube design. Trf radios do work well . Thank you, Ken from gpt ms
Excellent work. I love those old Practical Wireless projects. You did a brilliant job. Have a great Christmas and thank you for a cracking channel.
Nice project!
lots of fun work that today is nothing more than an app on your mobile smartphone.
Really enjoyed this Michael, thank you. That's some fine cabinet work!
Merry Christmas to you and yours.
I like it , happy Xmas to you and your family
Have a great Christmas Michael!!
Merry Christmas and a happy New year
Must be a trade issue with cutting wood straight as a now retired TV engineer I can’t either. I was OK with Fablon at Radio Rentals when we used to re-cover the teak cabinets in black. Great project Michael and have a great Christmas
I worked for the BBC on transmitters from the early 1960s. EF50s were used for a lot of RF low power units and they rarely needed replacing even running 24/7 for years. Well done Michael even if you mistook the suppressor grid for the screen grid!
I was pointing to the wrong valve, it's V1 where the screen grid is returned to cathode.
Sorry Michael, that appears to be the suppressor grid, the screens are up to HT+ and resulting HT on the kathode, suppressor grids are normally tied to the kathode or ground but can be used as secondary control grids. Keep up the good work, love your videos.
No, he was pointing at the wrong valve during part of the video. Yes, V2 screen goes to HT, but V1 screen is at V2 cathode potential.
Yes, you are indeed correct, I should have been pointing at V1, where the screen grid is returned to cathode.
The EF50 probably the most important valve during the WW2 made by Philips in the Netherlands. The basic valve for most radar sets display system. I suspect that is why they were used in the circuit as they were very cheap and plentiful.
While the Philips factory at Eindhoven was under Nazi occuption from 1940, EF50s were made by Mullard in England. Later Sylvania in the USA produced vast numbers of them.
Merry Christmas Michael!!
Many thanks for that
Nice job! Have a really Merry Christmas!
The first time I had ever seen a EF50 was at tech collage on a very old, even then, TV that seemed to have dozens of EF50s in every stage except those needing power valves. The big red can made them look lifeless as you could not see inside, not even the heaters.
Hi, Michael. "Jack Armstrong" here of "Television" magazine fame. I built at least one superhet valve radio in my teens. In fact I blew my Dad up with it: I fitted the reservoir capacitor the wrong way round! Anyway, your plywood cabinet looks just fine to me. Ideally, the plywood needs to be cut with a saw bench, using a fine tooth circular saw but you did OK. Merry Christmas, my friend.
Hi, Martin, good to see you here, someone gave me one of your books the other day, the sattellie screwdriver one.
@@michaeldranfield7140 Ooh, very rare. I'm not even sure that I have a copy.
That brought back memories from the late sixties when I was a apprentice Radio and TV engineer thanks to
What a shame we can’t hear the Light Programme again or the Goons show or Cltheroe Kid… I have a 1952 Bush valve set but all those wonderful old radio broadcasts are silent now.. I can think back as a child in the 1960’s sitting with my Nan listening to family favourites, it’s so sad we have lost all that
valves were on the way out when i started learning electronics :)
It seems to being a pretty good job! 👍
"Practical Wireless" - described by my tutor on the RAE course 1963 as "Camm's Comic".
i used to read practical wireless
Well done Michael! Nothing like a nostalgic project for the holiday season.
Many years ago I built a converter that received aircraft frequency broadcasts, 108-136Mkz, and rebroadcasted them on an AM 650-1700 Khz frequencies.
I also built a Knight Kit oscilloscope kit, sold by Allied Radio in Chicago, when I was in high school, arounf 1965. I still have it and it still works.
Question: I'm not familiar with the reaction control, what is that for? A gain control?
Have yall heard of BRUCE ROSENBLIT
He has made Transcendent audio with very very well designed amplifiers,
There is a 300b that can use rectified mains, and no output transformer and only 1 gain stage, 4 300bs in parallel.
Absolutely right on.
The schematic is in a very informative book Tubes and Circuits.
Hes the one that makes sense, out of all the other recirculations of circuits, this guy explains it without confusion or obfiscation.
dont know if i have that particular issue, but i do have a load from late 50s to late 60s, most with the original free 'blueprints' in the ones that had them, but i have that circuit in a 'practical wireless circuits' book, always wondered how well or not that circuit would work! i have a radio that was 'home built', using 3 EF50s, but a more 'normal' circuit, i think from a 'wireless world' magazing doesnt work very well , plus another home built one. in style of a wood cased pilot major maestro, normal superhet, and works fairly well, and yet another one with a unique style case, also superhet, doest work too well !
Realy nice project . Interesting design , does it produce alot of heat and how many watts does it draw
Total HT current is only 20Ma
3:57 what's making that beeping? for the last few weeks or so I've been hearing that exact same beeping in my street's corner shop.
Cctv, system, so senststive it bleeps is anything moves in the video.
I am exactly the same with wood, can never get a good result! Metal, no problem! I have that issue of WW, interesting. Impressed that you had the metal rectifier! So, come on, own up, did it work first time?
Yes it did work first time due to the ready made coil, but for safety I did power it first from a bench power supply just to make sure there was nothing amiss.
Nice work. Where did you get the chassis from? Merry Christmas
Had it a long time, someone was making these and selling them on e Bay, not cheap though, think I paid about £20 but it's good.
wonder how later valves such as EF91s, EF80s, or even high gain frame grid types EF184s would work? EF91s were certainly used a fair bit for home built stuff maybe a EF184 first valve feeding a PL84 output, for a bit more oomph, PY82 rectifier , and a nice big hot dropper resistor 😉 live chassis, of course, but class Y2 isolator cap for the aerial..??!!
I can receive radio Caroline on my AM radio in Antwerp 😃
Crikey! G3 is not the screen grid. The volume pot is wirewound because it's across the OPT secondary, not because of the miniscule V1 cathode current. Nice build though in spite of the schoolboy errors
You are of course correct because I was pointing to the wrong valve G3 is the suppressor grid, it's valve 1 where the screen grid is returned to cathode potential. A slight mistake in my un edited video.
What you are calling the screen grid is actually the suppressor grid, the screen grid is returned to HT, perfectly normal. It makes no difference using an RF pentode at audio, the limitation is in anode current , not relevant here because of the low volume anyway. The radio is simply a regenerative detector with one audio stage, nothing very suprising at all.
Of course your correct, I should have made reference to the first valve where the screen grid is returned to cathode, little mistakes always creep into my videos as there completely un edited now.
I made a regenrative radio using two EF50s. The design came from a book "Fun with radio". It was probably a good design but my choice of placement of the components wasn't. Skill was needed when tunig it in, otherwise it screemed somewhat. It picked up Luxembourg on 208 metres really well and then re-transmitted it on long wave!
I'm a bit confused. g3 is always connected to cathode to catch second emision electrons. g2 is on B+ and that's ok.
Slight mistake in the video, I was pointing to the wrong valve, G3 is the suppressor grid, irlts valve 1 where the screen grid it returned to cathode.
@michaeldranfield7140 oh, that's different story. I was reading some russian literature on the subject and i saw the same thing. They say that it is some kind of AGC or negative feedback. It makes some sense but I haven't totally understood the principle.
May i ask what the difference in the terms "valves" and "tubes"?
Valves is the British term and tubes is the American term. We call CRTs tubes in Britain.
@johndunleavy ok very good. I figured it was a language thing, however I was unsure. In America in the past people would call the CRTs picture tubes.
Would have been nice to see more of the construction of the radio but thanks for the video.
Very weird circuit. TBH, with a few more components you could have had a conventional volume control with coupling capacitors, and an audio output valve with a much lower value cathode resistor. No need to mess around with bias etc.
I think the EF50s were chosen because there were plenty of war surplus ones available in 1955.
I think your point about negative feedback is hardly relevant considering it is an AM receiver and TRF so plenty of distortion to begin with.
A QUOI Sert de dire E E E E E a Chaque fois!!!!c'est trop NUL!!!!!!!