VHF 2 Meter 829B Push Pull Class-C Vacuum Tube Amplifier
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- Опубликовано: 5 окт 2024
- A classic VHF push-pull amplifier probably designed in the 1950's that was a popular article in Amateur Radio publications showing VHF and UHF equipment. It is a push pull, tuned grid, tuned plate amplifier running class-C primarily for FM transmitters.
Wow, you triggered some great memories with your 829B video. I started out with a Heathkit Twoer in the early 60s. In those days, there were no repeaters and limited commercial equipment. The first thing I did was to build a nuvistor converter coupled to an ARC5 army surplus receiver. I started to hear a lot more stations with my 8 element antenna at 60 feet, but they couldn't hear me. I was in high school at the time and had a very limited budget for equipment. Fortunately, there was a great army surplus store that had everything I needed to build just about anything. My next project was to build an 829B Class AB1 linear amp to be driven with the Twoer. I knew a broadcast engineer that gave me a used 829B from the FM station where he worked. I found a surplus silver plated piece of gear, some kind of cavity resonator, that became the chassis for my amplifier. The power supply was built from scratch and used large oil filled capacitors, a huge choke, VR tubes and heavy power transformer. With that combo, I started working stations over greater distances. About this time I was getting interested in SSB. One of my mentors gave me an article that described building a six meter phasing type SSB transmitter. I scrounged parts and put it together. QST published an article about a six-to-two meter transverter based on Compactron tubes so I built that. The nice feature about a phasing type SSB exciter is that carrier can easily be inserted to operate in the AM mode since there were few SSB stations on 2 meters. Once again I was able to hear distant SSB stations but the 829B amplifier just wasn't enough to be heard. My final 2 meter project was to build a 4CX250B amplifier. I live in Michigan and managed to work 14 states, the furthest at about 900 miles away. By the early 70s, 2 meter repeaters and FM became the dominant mode and AM/SSB operation faded fast. I lost interest in 2 meters and gave all of the equipment away when I went to college. It was great fun and led to a successful career as an electronics engineer. Now that I'm retired, I'm getting back to designing and building receivers, test equipment and other stuff just for fun.
For the first time I see "in metal" that I saw in old books on VHF.
the 829b is 2 ea 6l6 tubes in a single envelope with short leads for vhf. 64 watts is great output indicating very good efficiency.
Your a very meticulous builder, shows your pride and knowledge. Thanks for sharing!
The moment you realize you don't even know what you don't know.
Excellent!!!73
What a great old is amp build.
Many of the newer 2 meter mobile and desktop radios exceed 64 watts out of the box. It is neat to see some of these rigs.
three of them still working my grandfather built 1 and I built 2 :)
The lost art of ham radio. Reminds me some of the plumbers delight with a pair of 4X150's or 4CX250's.
I have always considered building that plumber's delight you speak of but haven't gotten around to it. I did build a 4CX250B two meter, class-C amplifier in the late 1980's and it would deliver around 500 watts to the antenna. That is when I acquired all the VHF Bird slugs going form 5 watts to 500 watts. So much power the RG-8 coax would become warm. I sold it at a ham fest in Midland, Texas around 1990 time frame.
@@ElPasoTubeAmps Thanks for the kind reply. Ex-Varian-Eimac'er OM here. 73' keep building/restoring.
I started to build the plumbers delight for 2 meters with 2 of the 4CX250F in the late 70s but never finished it.
I would really like to see one working. I see some videos using 2 in parallel for 11 meters.
Very nice, thanks for sharing.
EXCELLENT.
Finally something "without arduinos/raspberrys/smd´s" ;) (...I´m an "old fashion´ ham"...)
Many thanks for share this very interesting video..!
Kind regards de LU4EYW.
I guess it is kind of randomly asking but do anybody know a good website to stream new movies online ?
Classical design.
nice build David
You can easily make those coil clips yourself! you can get aluminum OR tin from anywhere.
of course you use tin when you also need to solder it!
Tin can be found everywhere, for example in the kitchen!
(I even sometimes cut lemonade cans - OR aluminum OR tin)
bending aluminum or tin, what shall I say! is so easy to do!
you could also make tuning capacitors with the tin version.
Healthy and Friendly Greetings from the Netherlands!
Rob
Why not make the clips? They look pretty straightforward. Hams are known for constructing parts that are “unobtanium“.
Very nice job and thanks for sharing this with us. 73 Leo.
nice build :)
.....Lovely thing!!! I have a Belcom LA106 2 meter linear using the same tube, but, it needs 10 watts of drive, and has a very odd grid circuit. The link coupling you constructed looks much simpler, and straightforward,... Could you tell me the driving power from your HT in the video?? I'm hoping to modify my linear to the same as yours, and get a fair output from a 3 watt drive power,.... Thank you for your video, Fred G4ZWI
why did you not go with 2x 4CX500A ceramic vacuum tubes instead of a glass vacuum tube.
This 829B is especially made for VHF and I had plenty back then - still have a few spares. Some time later I did build another 2 meter amplifier with a single 4CX250B that would deliver 500 watts output and sold it soon afterwards at a hamfest in Midland, Texas probably 30 years ago.
Great video. By any chance do you have any schematics for 829b as a P-P audio amp power tube? I'm looking for an old, like they're not all old, but this was a series-P-P audio amp. Thanks for the video and any help.
Pete Millett is a great source of information. In this example, he uses them as SE amplifiers. I personally would use them as push pull.
www.pmillett.com/829b_amplifier.htm
www.pmillett.com/images/829b.PDF
@@ElPasoTubeAmps Thank you!
@@ElPasoTubeAmps Just check it out. Looks great.
I had a magazine where they took one tube connected in series then put two of those to make a push pull amp. It takes four FU29's for stereo but that's why I'm wanting to build one. I have a about twenty of the old 829's in da box.
Also by running each tube in series they could use them with, as I remember, a 35% linear tapped OP trans.
You can't normally do that with 829's due to having interconnected K, beam grid and I think G2's are in there as well.
But hey man thanks. I'm working on a 6V6 thingy at the moe buttt.
@@tayro7265 Something that crossed my mind. There are definitely some tubes that can not be run in a triode mode, i.e. the screen at plate potential. One such tube is the Eimac 4-65A. Eimac specifically warns about this. It has to do with the internal geometry of the tube construction. The screen must be at the potential suggested in the datasheets otherwise, the tube will be destroyed. I do not know about the 829B. It is definitely worth looking into before possibly destroying tubes. I mention this because of your comment about the 35% taps. These taps put the screen at the same voltage as the plate and is a form of triode mode. Just thought of this and figured I would throw it in. Investigation may prove that the 829B can have its screen at plate potential. 73
@@ElPasoTubeAmps Yes Sir, that's why I'm fishing for info. Again as I recall the schematic did have a dropping resistor. However if it turns out that resistor is some 5m @ 150w, then yea can't play that game.
I can't remember the name of the amp. It was a mono guitar amp. I do remember the magazine splashed "With the power of the 829B" across the schematic. Just to make it easier to not be able to read it.
With it being a class C amp, is there not a need for a low pass filter at the output to cut harmonics?
No, I have never hear of that need for a class-C amplifier. I just built a grounded grid (GG) 3-400Z amplifier biased for class-C (-90V on the grid) and plate modulated it running to run AM. I noticed on my modulation monitor my negative modulation peaks are higher than the positive modulation peaks and just read this is because the grid voltage (-90 as mentioned) is added to the plate voltage (3200 VDC) during the negative cycle of modulation. So, now I am in the process of adding a keep-alive voltage prevent over modulating in the negative direction. I use this same keep-alive circuit on another AM transmitter and it works very well. Here is the link in case you are interested.
amwindow.org/tech/htm/3diodeka.htm 73 WA4QGA
@@ElPasoTubeAmps OK interesting---I was just curious. Maybe it's just that tubes are cleaner than solid state devices, so they don't generate as much harmonic content? Or maybe the tuned circuit part of it limits the spectrum to keep it clean. I just had in my mind that any non-class-A amp would have a decent amount of distortion which would manifest as unwanted harmonics on the output.
I think the distortion is there as a class-C amplifier conducts for less than 180 degrees of the positive cycle and the collapsing fields of the resonate plate tank circuit provides the opposite half cycle (amazing, isn't it...) and distortion is probably pretty high for modulated audio but I think we can survive 2, 3, maybe 4% THD without too much trouble especially if it is just voice communication. It would be interesting to know the distortion level of a commercial AM station. Class-C amplifiers work great for plate modulated AM and for directly amplifying FM signals.
Quem tem pouco estudo. Mas tem um básico em eletrônica vai perceber que se trata de um transmissor em 2.m. plush pull.
Que clase de idioma tan retorcido es ese?
I wish I could get a copy of the Schematic? Could someone do me a favor?? TIA
I found this on the Internet but I can not find the original ARRL article. If I ever do find it I will post it.
www.funkamateur.de/tl_files/downloads/hefte/2016/AN%20829B%20DUAL%20BEAM%20POWER%20PENTODE%20HF%20TRANSMITTER.pdf
Here is another one. BTW - the "RCA Ham Tips" is a good thing to search for on the Internet. Also "GE Ham Tips". Lots of good articles from years ago.
n4trb.com/AmateurRadio/RCA_Ham_Tips/issues/rcahamtips2202.pdf
@@ElPasoTubeAmps Thanks, my friend! 73 KD7TWW
John, can you get in touch with me? We have a few interests in common it seems. Ham/RF, Audio, Astronomy... Would love to pick your brain on some topics. Or, at least share some data. I hope you can find me by my "Google/RUclips" info.
Did you have to reform the HV electrolytics?
You inspired me to drag out a box of probably 200 or more electrolytic capacitors from the attic where they have gone thru El Paso summers and winters for a lot of years - as much as 20 years up there and they may have been 30+ years old when I put them there.
I started measuring and tinkering and had mixed results in reviving them.
In the case of this amplifier, I just plugged it in and turned it on. That is usually the way I do it.
I will not deny that bringing up electrolytic capacitors slowly might be a good thing but just turning them on seems to work for me virtually every time. I have been doing this more than 50 years and rarely do I have issues with electrolytic capacitors - mostly they just open up and become pico Farad level. That is my experience.
I tried making the video but the results were so varied I am not sure a relevant video can be made that will say one way or the other if there is any difference between slowly starting them up or just putting the juice to them. I can't do one procedure then the other on the same capacitor so we can never know. I am still thinking about it.
👍🏻🎙73's kd9oam
Entendi um rádio valvulado AM FM .SOLTAM UM VÍDEO SUPER INTERESSANTE NUM PAÍS A ONDE O POVO MAL SABE O PORTUGUÊS .LAMENTAVEL.
I see no tubes. I see thermionic Vales, but no tubes.
Wow...Love it , good Job David, always interesting stuff
zs2cx
we fixed the 4cx1000a thanks to your your notes.
That is very nice to hear. Not just everyone can tame the 4CX1000A. Obviously, GG amplifiers are so much easier to deal with but it seems we both like the challenge. 73
Did you try and industrial supplier like Graingers? Looks like something from a large motor start, old style equipment.
A good gentleman directed me to DX Engineering where the very ones I have are sold. I will keep Graingers in mind for possibly larger ones. Thanks...