Homebrew AM Transmitter Part 1

okay this is w5h ro here's that am a Homburg transmitter I have built back in the early 90s and had on the air I uh I started gathering parts for it sometime in the late 80s at mid to late 80s and I had it all assembled and ready to go by out of the early nineties probably like 92 93 this is the one he used to be brought as a bar because the the negative peak when I modulate it would go way too far negative so I never could turn the UH the speech amplifier up too far I had to keep it turned down and keep it from splattering to bands like 20k seeds wide when I did but is the wrong kind of splatter you know it was like wow but it sounded beautiful anyway uh the original design I actually found my notes they were in a folder and envelope and look there's the dimensions when I put this when I designed this thing back in the 80s there it is there's how I wired this at the high voltage and everything into power the AC coming from the wall and and there's the the by supply that I made for the the for 400 CG and then there was the loading cap arrangement I used for the the loading here there's the loading the verbal loading cap down here and then there's the switch for it and it's got all Peter doll transformers it's got a modified custom one it's custom one four eight tens to this tube here yeah the CG the carbon graphite version of the the four 400 has more power dissipation but it's custom bound for the voltage I'm running and that to to modulate it and there's the driver it's the kW one driver transformer or the desk kilowatt Johnson desk kilowatts exact same transformer and there's the the plate transformers I had there's actually two supplies in this transmitter there's a one for the modulator and one for the RF and they're both capable of 800 milliamps it's overkill but hey you know can you say continuous continuous duty times infinity or something and there's the swinging choke see I don't have a regulation problem at all xxx v Henry one amp chokes perfect so anyway but I have all the documentation of how I originally did this now I moved out here to California in the Bay Area in 2000 January of 2000 and this thing sat in storage until 2009 when I got a u-haul truck and my ex-wife and I drove it out here and a big u-haul with all my other stuff and they went to my our house in San Jose that I just sold here recently just I mean into February 2020 here I got out just I got top dollar for just before the market crashed and and if you wonder where I am now I'm in Eldorado County California and I will be on the air some fat back on the air it's been like I've had like a 20-year dormancy I got on the air with some small you know low-power stuff in San Jose I'd be on time or two but I really have not been active since the end of 1999 that's how long has been it's been 20 years so anyway I was gonna actually do this last weekend but I went out in the garage and started looking and I can't find the cord that I wanted I thought I had a longer one this has got a whole big heavy-duty some type of like dryer power cable on steroids it's set up for 220 it's one of those industrial power cables and it's too big and I'm gonna rewire I don't have 220 here in the shock I only have 110 and I'm not going to put 220 down here anytime soon I am eventually gonna build a 4-1 thousand linear amplifier and when I do that I'm gonna go ahead and put the 220 in the then I might consider redoing this back to 220 but I'm gonna rewire this for 110 the problem is I've searched out in the garage and I went through all the boxes and that's the exact size power cable that I want problem is this tune are short I want to be able to rule this thing like over here if I want to and have it still plugged in if I need to work on it but that's the right size and I'm gonna have to change out the the thing here and the adapter here for the cabinet that that did the that diameter that's too wide office if even if I screw the screws down all the way it'll still it still it'll probably clamp on this skinnier power cable I'll probably have to go to Home Depot and find a heavy-duty power cable just like an extension cord the heaviest shortest heaviest one they make it just cut the other end off and use that but there's the swinging chokes and there's the kws one plate transformers in the back all the iron in this thing is was Peter doll custom back from the late 80s early 90s and except for like - there's a couple on the buy supply duct that's a mr. ham and there's one little one that I added up in here when I'm when I did this recent change to it a few years ago and Lee RF duck but it's all Peter doll iron and I'm just gonna rewire those plate transformers for the for the 110 input here soon as I get a power cable for it I thought I was going to be delery but I can't find it I thought I had one but I don't but anyway this is the bias applied deck for the 4 400 and that's going away that's going away I'm gonna have the t3 68 exciter with a sideband adapter next to it the SB 10 adapter that they're just the chassis not the front panel of it there's the SB 10 I'm actually going to make it to where I can run this you know with the at t3 68 excitation and I'm gonna grid modulate to 4 400 and that's what a modification I made this thing a few years ago and I just need to finish it up I'm gonna put a light here this used to be an input tuning for I I'm gonna I've gotten changing the input tuning on this thing because it doesn't really need it because the t3 68 exciter it's the way these things ran in the t3 68 says it had a short piece of coax driving the the grid directly it's long as it the coax the piece of coax is short enough it wasn't an issue I can even put some of those fear rights over it you know just to keep any RF and it worked beautiful that one but the thing about these t3 68 exciters is that when you spin the knob well it Tunes the circuits as it moves everything around the resist I mean the capacitance and the inductance and all that stuff so it it's auto tune and just by changing the frequency see it does I don't need to tune it I won't need to tune it will just be fixed there at the input so anyway but this what this is is I forget which position is a wish but one positions the relays often it's an AM it's gonna have grid leaked bias that's the change that I made it has a grid lick resistor in there now that's going through the current meter and all that stuff and then when I go here it's gonna switch it to a B bias it's gonna switch it's gonna force the supply voltage onto it externally and that's how I'm doing this and that's gonna have a little big round old-fashioned lights there it were just when I go to sideband it lights up so I know it's on the a B position I just need it indicator to make sure that it fits I'm gonna run it on AM that's not the light's not on that's the desk that's all detector whether it's in the right position or not but there's the 810 you know aint ten rat down there I've got a big current meter on it and here's this the speech amp and this DISA desti a bias for the the I'm using 683 drivers not to a 3s but the 6 volt version 6a 3s which are the same thing as 6 B 4G so they have produced a beautiful sound or low nutrients so anyway but that's what I'm doing I'm just going to go through it almost suiciding kid to find a power cable on man I what happened has done already but oh here's also in the is the the three diode negative peak limiter with the new-and-improved modified problem-solving double resistor circuit do not do not use one resistor like everybody's been doing there's a reason why you don't want to do that there's a there's a flaw in the circuit design and if when you add the extra resistor it bridges it over at the right sequence of events so the event doesn't happen that's created without it and basically what you do is these two resistors in parallel because they're all when the negative Peaks going down it's going to see both of these resistors essentially in parallel so they're gonna divide right so you've got to have say let's say like you needed a a 10 carries that 10k load for this whole circuit to work well you got to put two 20k in parallel like this they're not in parallel but they're in parallel all the way they're gonna the way when the negative peak goes down and that's what's important so if that's a big humongous significant improvement improvement in debt limit or design there is a flaw in the initial circuit and people just don't know it's there I discovered it and it's real and it causes additional splatter on the band's I guarantee you it does it needs to be corrected and that's how you fix it all of a probably a person I'll probably do an article and I'll put that on w5 h ro dot-com when I have a chance that that's that's going to be a future article that I need to rewrite and put it on there try to explain people why it needs to be done and you know that it's it's an it's important so anyway this is a this is pretty cool now I can't wait to get this thing reel it up again where did I put the I have the the bottom panel for it's in here and see I have a fan and it's going to it forces air it sucks air out it sucks air from the outside and forces it up to the base of the table but just a muffin fan and this thing here mounts inside the chassis on the bottom side is it directs us so it forces most of the air on under the tube socket because I'm not using a forced air cooled socket this thing had been in it had been pretty much in a you know classy configuration and it's running just low-power AM you know care I mean not low-power thing will do like 500 watts but carrier but still it's not the tubes just sitting there loafing and classy service so it wasn't really a problem but what I read that when I when I redid that change and I made that round piece of PVC the mounts up in there you could actually reach up here and you could feel the air coming out of these holes now just a little bit of finally death that's it gave us some circulation before the fan which is blowing air and it wasn't coming out the holes it was dividing off all throughout the bottom of the chassis so I'd like to focus it on this bottom of the socket and that seemed like it solve the problem cuz I'm just using one of the old ceramic tube sockets with the old clips on top of the chassis to hold the tube down and grant he'll make contact with the other chassis so it should work when I get this thing fired up I'm gonna go yeah and at night with the lights turned out and you'll see that the core thing will be lit up orange and when I modulate when you see the yeah you'll see it brighten up and that's the whole point gotta have that Yan a.m. phone if I can say it right Yin yeh em that's the problem seems like the older I get the more I have a the more the more trouble I have getting getting the words out correctly I think there's a name for that isn't there Oh anyway that's it for now I think did I have anything else to add oh yeah yeah yeah I've had two videos on my old youtube page but get my finger on the way the camera here I've had two videos which were the biased rework when I when I added the realizin I did the bike cuz the way I had this circuit that was I had regulated supplies they were too stiff I wanted some flexing but the way they came out they were just too stiff for the tube and I know why because it was designed for a pair of four for hunters and not a single one so addict the Transformers we're supplying extra current and I just the values didn't come out right so it was too stiff so what I'd modulate it forced the negative peak down too far plus on the the transformer there was two taps and I used the one which produced the smallest secondary voltage for the screen and I had the screen running only at 400 volts well you know what went over whenever I used to run this thing years ago the grid drive had to be a little bit higher but the screen curd always if the screen current always ran ten milliamps too hot it's because the screen voltage was too low and I didn't realize I was on the wrong tap on that on that the primary on that transformer and that's what happened so I did eventually switch that and it came up to the full 500 volts because this tube this is a this is not like it's not like the iMac for 480 tube or this carbon tube even the the specs on it where is it it's it's it's 500 volts C or is it no it's 600 volts and what's fun we went looking for Class C service here we go yeah there it is 500 volts right there amplitude modulated carrier conditions below 75 mega cycles I love it when you see MC and not bigger Hertz anyway DC screen voltage 500 DC grid voltage is 200 and I've got to worry yeah that's that's where it is with the grid link I've got an 18 K grid leak resistor I believe now for the control grid that's how it's gonna work and then when I switch it it's gonna be a different bias for the put an ad for the sideband excitation so although like I said you're gonna see but when I did the original bias supply I I was doing the rework on this thing like I said in San Jose and there's two videos that have been on YouTube if I could get this story to come out there's two videos that are on YouTube that I've had on there when I back when I did that reworked and I've just almost got completely finished it was almost completely done and I'm gonna make this video part 1 because this is gonna be this is kind of like hey this is what this was about you know this is the the homebrew transmitter this is part 1 but I'm gonna put those two old videos I'm gonna make them part 2 in part 3 because hey we gotta you know I gotta get to where this whole series makes sense and then as I get this thing powered up start doing more there's gonna be like a part you know a part 4 part 5 you know etc etc it'll continue to like get this thing on the air and back in service so this is w5h ro

Channel: Amateur Radio Station W5HRO / 6

Views: 5,755

Rating: 4.9587631 out of 5

Keywords: Receiver, Amplifier, Transistor, Antenna, Modulation, Vacuum, Beam, Linear, AM, LF, Capacitor, LSB, Frequency, FM, Dipole, Vertical, DX, SSB, Inductor, Shack, QST, CQ, RTTY, ARRL, Coil, Resistor, Wavelength, W5HRO, USB, HAM, Analog, Amplitude, CW, Electronics, Yagi, HF, Amateur, Meters, Transmitter, SWR, Tube, Hertz, Megacycle, Kilohertz, Radio, Zepp, Coax, Balun, Tuner, Matchbox, RF, Gain, AF, IF, LO, Mixer, Signal, Generator, A3E, Oscillator, Roller, Trap, Load, KI5SG, FET, BJT, Nuvistor, Ohms, Counter, Modulator, Class B, Class C, Class D, Class E, MF, J3E

Id: lt-hOjUoOIs

Length: 15min 36sec (936 seconds)

Published: Fri Apr 03 2020