Plate Modulating The Mighty 833A 

It is a dream-come-true modulation transformer but after some 60+ years I imagine the lacquer dried out. There is a comment I left below about how I put it on a mat and then an insulated ammo box over it and quieted it down. Problem with this approach is the HV leads necessary to and from the transformer. Got to be safe first... thanks for your thoughts.

I think, as you mention, part of the issue was that it was sitting on metal. I made a couple of comments above of how I set it on a rubber mat and a large insulated ammo box over it. Also, I added some 0.01uF 10KV capacitors across the primary and secondary to squelch audio harmonics and that helped a bit also. I have never dealt with this level of HV modulation. Audio peaks were no doubt reaching 7KV+ and things start happening at those levels that don't happen at 3.5KV DC. I am doing OK - I suppose - life has changed so much - I have been alone eleven months now. Just wish I had more energy to work on projects and post videos and communicate with you guys.

@@ElPasoTubeAmps Good to hear that you are doing OK! I wouldn't worry too much about your projects and posting videos right now. You need to take care of YOU! You have done SO MUCH and been a wealth of information and your knowledge that you have shared is a treasure! Not go get too "out there", but you are NOT alone! and NO ONE can tell you to "get over it"!!! That is up to YOU and ONLY you! Just take care of yourself! You have SO MUCH to offer. I have lost both my parents (2009 Mother, 2019 Father) and my sister (1985). I just try my best to keep my projects going, which I love to do, and try not to become a recluse. I very much enjoy all your videos as they have tons of information, are sometimes comical, and I really like your attention to detail and your craftsmanship! You do NICE work! Anyway, I wish you well and hope to see many more of you, but do take care of yourself! Bill

Very nice that you run a pair of 812A in your transmitter and modulate with 811A. I would love to QSO with you. I have a James Millen amplifier that runs push-pull 812A with swinging-link coupling right from 1947. It works beautifully. My modulator is homebrew and runs a pair of 4-125A into a BC-610 modulation transformer. Here is a link showing it a few years ago but I have since put it in a tall cabinet with modulator and power supplies. I may get some help dragging this transformer out into the hot El Paso sun and loosen up the bolts and see if I can get some thin varnish to seep down into the laminations. Putting the transformer on a rubber mat and under an insulated metal ammo box did solve the problem but it takes up a lot of extra room that way. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-OkYS4TrTqrw.html 73 WA4QGA

@@ElPasoTubeAmps Greetings, It would really be interesting to do a QSO with you, but my station is in Santa Catarina Brazil. As I don't use a directional antenna but a Levy antenna, which in a simplified way is a dipole with an open line, I think it's a miracle that we manage to perform a QSO in AM, maybe in an high band. Yes, one solution to prevent the modulation transformer vibration from propagating through the chassis is to use a rubber damper or make the transformer floating. But the best solution is to lock the coils and iron blades with some kind of resin or varnish, transformer varnish, when new is very thin, but if necessary it can be heated. Using a pressure cooker that holds the transformer inside, and a vacuum pump, which can be a used refrigerator compressor, it is possible to make a vacuum chamber to impregnate the transformer. The vacuum causes the varnish to penetrate inside the windings and blades, allowing the device to completely lock. Finally, triodes are the best valves for plate-modulated AM operation, due to their naturally quadratic characteristic. I am part of a group of Brazilian radio amateurs who restore and preserve old communication equipment, all of which only operate with valved equipment, usually homemade. This is the fundamental amateur radio. 73 PP5BMS.

@@mauriciosinigaglia4761 I hear Brazil occasionally on 20M. I have a hexbeam for 20 and an inverted-V for 40. That is all the room I have for antennas as my yard is small. I have your call and if I hear you on, I will do all I can go contact you. I don't think the conditions are reliable enough for a scheduled call but we could try if you want to - SSB to start with, of course. I need to get back on the 833A project as I rolled the transmitter into another room for now but I haven't forgotten it. I have a lot of pictures of equipment on my QRZ page. 73 for now. WA4QGA

I tried other modulation transformers that are potted and did not have the feedback issues but I have learned before, and again here, impedance matching is very important. We can use a 3.8K or 5K or 6.6K, etc. on a 6L6 amplifier with pretty good results with any of these impedance values but not at this level of three and four KV and then modulate it doubling the positive peaks. Impedance matching has to be correct and the big UTC multi-match transformers does it perfectly - except for the "talking" of the laminations so loud we get acoustic feedback. It wouldn't be fun if it was too easy. 🙂

I did just that - I used a kitchen type floor mat to set the transformer on and then put a large ammo box over the top that I lined with Styrofoam and it did stop the sound and feedback. I just got a little burned out and set the whole project aside for a while. I will come back to it soon. Thanks for your thoughts.

@@ElPasoTubeAmps Right on... you're welcome. 🙂

Hi Manuel - I do remember you writing some time back but if I read an email and don't reply at that time, it often time slips by me. Did I not reply? This project is in the corner for the moment and I have some smaller ones I am dealing with but thought it might be entertaining. Hope you are doing well.

@@ElPasoTubeAmps Yeah I did not see any reply, it was about some code I wrote to easily automate measurements with gpib instruments without using all of that weird commands. If you would like to know more hit me up! I am doing fine, but at the same time dealing with some health issues, fortunately nothing really bad but I am still having some trouble. How about you?

I see the value in superglue. Some years ago I built an amplifier and used ceramic sockets that needed a notch to orient them and they were held in place with a wavy-washer. Since I do not have that special punch with the little notch, I could not secure them from being a bit lose and want to rotate. Somewhere on YT, I saw where a fellow solved that with superglue. I use it and it works to this day and I listen to that amplifier daily in my backhouse. I have never tried it on a transformer. The paint on this transformer is very nice and thick even though it is probably 60+ years old. I don't know this but from what others have mention in comments below, it may not be uncommon to have an uncomfortable amount of audio feedback from these large audio devices. Think about the amount of what we can hear around 1KHz from the best 25-50 watt audio transformers and multiply that to 1000 watts. The solution, so far, is to give it its own space in an acoustic chamber. This is only part of the problem... Now I am modulating a 3000+ volt DC source where audio frequencies must reach 6000+ volts peak. This is a big deal. Talk about needing HV capacitors and connectors...Things happen fast and violent at these levels if everything is not right. I have shorted 5000 volt plate blocking capacitors, arced meters to the chassis and exploded high voltage Millen connectors. It is enough to keep you scared every time you initiate HV. The rubber mat and insulated ammo box solves the acoustic issue along with high voltage spark plug wire. I have rolled this monster into the corner for the moment. It makes one understand why 1000 watt AM transmitters from the 1960's and '70's are the size of fridge and weigh 1500 pounds. Thanks for keeping in touch. I do the best I can to keep in touch with you good gentlemen that I have had a friendship with over the years even though I may be slipping on responding a bit lately.

It is only during modulation and is probably more of a common problem that I initially realized for KW level audio transformers. I feel sure the age of the transformer has something to do with it also and it being an open-frame transformer. I have another AM transmitter that uses a UTC type round and potted transformer and even with it, if I get the microphone close to it, it starts to feedback at a high frequency just like a microphone and speaker. I did discover that putting small value capacitors across the primary and secondary did helped calm the issue but it was best solved by putting it on a rubber mat and under a sound insulated metal box. I think it is pretty much the whole voice frequency range that is the problem but I like your suggestion of an equalizer. I have gotten more good thoughts for solutions from you guys than I found across the Internet searching for a solution. Thanks... stay safe.

@@ElPasoTubeAmps Always enjoy your videos. Please keep doing them!!!! Robert

I just looked up your RCA BTA-1R and found its manual at the BAMA site. I love to look thru these old manuals. I see it used 4-400A for RF and modulation. Looks a lot like the Collins transmitters. It seems Gates stuck with the 833A for both. Surely there is some way to "pot" the transformer so that it does not have to be on a rubber mat under an insulated steel box like I have done. I wonder if it would help to tape off the connectors and then paint/dope the whole transformer in a heavy coating of maybe epoxy? Maybe I could put my transformer in the metal ammo box and fill it with epoxy... then it would weigh 120 pounds - maybe not. 🙂

We can hear the OPT "talk" in even good stereo quality audio transformers as I am sure we have all heard before especially with a tone at 1 KHz but this is at a different level all together. Very loud and gets right back into the microphone. I assume it is mechanical vibrations of the laminations. This transformer weighs 85 pounds so it is not an easy thing to toss around and play with. I did tighten up the bolts on it for no help at all. I think all large audio transformers like this "talk" under modulation but I figure this one is worse because of its age. I have read that it can be vacuum impregnated with lacquer but I don't know where to have that done. Putting it in a sound proof box seems to be the homemade solution - at least for now.

@@ElPasoTubeAmps maybe you can make a vacuum chamber and use one of those eBay vacuum pumps

Are you looking for the transformer for the 6B4G's or the 810's ?

I need to post a new video of this AM transmitter. I have set-aside the 833A for now and used a grounded grid (GG) 3-400Z amplifier that I biased for class-C and plate modulated with the modulator in this video. It is running good. I put the huge modulation transformer on a thick rubber mat and covered it with a internal foam insulated large ammo box. I cut a hole in the ammo box for the HV wires to come thru and use spark plug wire for connections to the amplifier. It quieted the transformer down so I have no acoustic feedback but I can still hear it "talk" a little bit so I ordered some stick-on sound deadening material. As for RF feedback - I put 2.5mH RFC and 100pf capacitors in the audio lines and that solved that problem. I am on the air with it and pretty happy but still need to do some cosmetic and safety work with it. Thanks for your thoughts and comment. 73

Not any more. I have had quite a few over the years as I was given several pulls from an illuminating radar station from WSMR where I worked 20 years. Lots of years ago I built a 4-1000A amplifier but did not have a PS of at least 5KV to run it so it turned out poorly. Even 4KV is not enough. Another thing is if I want to go significantly larger than what I already have in two transmitters with 1.5K output, I would need to go to 3000 watts (a pair of 4-1000A) or so, and it starts to become just crazy big. At 3K watts output, the chance of arcing my hexbeam becomes real and I can't climb that little tower any more. It is obvious I love the power but I am trying to keep myself satisfied with only 1.5K watts. 🙂 73 WA4QGA

@ElPasoTubeAmps totally understand that. I want to get a pair of 4-1000 for a future build. I run a pair of Penta Laboratories 3-500zs now. Trying to take my time finding what I need for the next build

@@bluecollarlogger8436 Push-pull 4-1000A could deliver more than 5000 watts output with 6000 volts on the plate. Ham radio operator dream come true - but - why not go to push-pull 4CX3000A for 12KW output. Run AM so your neighbors can understand your modulation. One of my neighbors tells me he can hear me sometimes but can't understand what I say and sometimes he can. I try to explain to him the difference when I run SSB and AM. There is just no sanity level in it - I love it... stay safe.

@ElPasoTubeAmps I've just always been a big fan of glass. Nothing like seeing them baby's glow

It is a monster modulation transformer - too big to handle and "play" with but with all the taps it has, it will match practically any set of push-pull modulator tubes to any RF amplifier load. I will get back on this project soon. Sometimes I just have to let a project rest for a while.

Ten four good buddy 👍be very careful high voltage can hurt I work on a little guy 1 time and when I grab it bottom got me it was just 1 tube little it only done 100 watt ouch got sb 220 and now when I clean it I discharge it real good actually leave it unplug for couple days

@@benjaminmeadows1380 Yep... the HV in a SB-220 could be a one way ticket to the next life...I am careful and methodical in working with HV but I also know a bit of luck in a couple of cases has probably saved my life. Stay safe. 73

Ok Yelp lot volts knew a guy back in day in Florida he had a system in back of van he did shootouts he got fried with that they found him in the van dead so sad that day back in the early s 2000 I been in radios for 25 years so seen them monster amps

@@benjaminmeadows1380 Working with high voltage is kind of like having a cage full of pet rattlesnakes. Funny the things that we enjoy that can kill us.