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Art-13 questions in a 8xx modulated by 811's




 
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Author Topic: Art-13 questions in a 8xx modulated by 811's  (Read 1312 times)
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w9jsw
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« on: March 30, 2018, 09:21:41 AM »

I have been reading a lot of old threads on ART-13 usage. However I still have a few questions.

I have an ART-13 that I plan to use in a 8xx modulated by a pair of 811's. Jack K9ACT used a 810 for the RF tube with good luck. I have not yet decided which one I will use but leaning that way. 812 or 813 is another option. I want to end up with around 150-200W of carrier and just one RF tube.

Here is Jack's schematic (showing a 811 - adding the 810 is straightforward by adding a bias of around -120V for cutoff and a 10V fillament).

see attachment

Anyway, I have a plate transformer that can give me around a 1300V supply being designed. I was using it the way Jack suggested with a choke and a 4uf oil filled cap, however he was using a much larger mod transformer S-22 and no reactor choke. So it was suggested by quite a few here that I use a shunt feed modulator to allow me to use the ART-13 here. As I read the article by Genaille, he moves the reactor from the supply up to being connected to the modulator along with a 4uf oil filled cap, right?

If I start out using just one supply to feed both the modulator pair and the RF tube, will I still get good power supply regulation for the 811's? Should I be planning to keep a 8HY choke in the PS and add a second one for the reactor? I would kind of like to get this running on just one supply for now, but may then add a separate supply to the RF later to get higher B+ and a bit more power.

Also, how do I compute the total amount of power this supply must deliver for the 3 tubes?

John


* 811_am.jpg (115.9 KB, 1185x1025 - viewed 58 times.)
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« Reply #1 on: March 30, 2018, 10:06:25 AM »

I know itís none of my business and hope I donít offend but what are you going to gain by flogging a seventy year old transmitter just to get another fifty or seventy five watts? Whatís the limit of how hard you can hit the modulation transformer in the ART-13 before it fails? Or are you planning on building an external modulator with a bigger transformer? At what point would building a new modulator PA deck be just be as easy?
Donít get me wrong, itís your stuff and you can do whatever you want, I just look at this like putting a big block Chevy in a Ford model A and when you add a bunch of horse power on one end often things on the other end tend to fail. Then again a big block Rat Rod can be cool.


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Todd, KA1KAQ
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« Reply #2 on: March 30, 2018, 10:31:42 AM »

I'll add a bit to what Ray has said.

I've heard stories of the ART-13 modulation transformers being badly abused and surviving, so I suspect it's probably a strong point in the transmitter. That doesn't mean all other components are, however. Keep in mind that, while built for reliability with some level of a safety margin (military gear tends to be overbuilt for what is expected of it), it was also built to a specific requirement. Wander much beyond that and you could be asking for problems.

For comparison, I'm currently working to resurrect a 1941-contract Meissner 150-B military transmitter. Configuration? 813 modulated by a pair of 811s. Manual states 150 watts out of the box, but of course the 813 is capable of much more (ask K1JJ). When these transmitters hit the surplus market after the war, of course they were snapped up. And of course, they were pushed for more output.

Not a lot of info out there, but I have read several accounts of users trying to get 200-250 watts or more out of them and succeeding - briefly. The problem not being the tubes, but the other components used. Seems today users are content to get 175 watts or so out of them and play it safe.

So you may be fine with the 813 and a bit of tweaking, testing, and so on. But also as Ray says, it's your transmitter. Experiment away. ART-13s are anything but rare, many parts are still available. No one is likely to miss it or cry if you blow it up, except you. Wink

You've got the right approach - ask a lot of questions and move forward slowly. Chances are you can make it sing somewhere in the 150-200w range without a lot of trouble.
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w9jsw
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« Reply #3 on: March 30, 2018, 10:38:10 AM »

You are not offending me, however, I need you to explain your comments further. This is my first effort into AM tube transmitters and the concepts are fuzzy. I currently run a homebuilt SDR with 50W peak on AM and virtually no one can hear me. I thought it might be fun to get into some of this older technology and learn something. I could go buy a big linear and be done but there is no fun in that. I like to build stuff...


John
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AJ1G
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« Reply #4 on: March 30, 2018, 10:43:04 AM »

Even when run stock at nominal 1100 VDC on the 813s and 811s, the  ART-13 stock mod tranny has a significant amount of distortion below about 400 Hz. Fine for milcom audio, but don't expect anything like broadcast quality from it , especially if you try to push more power through it.
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Chris, AJ1G
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w9jsw
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« Reply #5 on: March 30, 2018, 10:59:48 AM »

Jack got a respectable 125W out this simple transmiter using an 811 for the RF tube. Maybe since I am using a weaker mod transformer, I should drop back to a more conservative tube pair in the modulator perhaps 807's or something similar. Or perhaps chalk this ART-13 purchase (NOS $75 bucks) a beginner's mistake and put it back on the 'bay and go looking for a better modulator.

another question - I am going to use 1N5408 diodes in strings for the bridge. Should I get rid of the choke based power supply and the oil filled cap and use a capacitor input supply like W8JI suggests in this article. My plate transformer is a 1kv CT model? I am more comfortable with this sort of supply.

https://www.w8ji.com/designing_ham_transmitter.htm

I could use the split supply version and go looking for a modulator circuit that runs at around 700 volts.

Back to the supply, when I build the bridge, do I use ceramic standoffs or can they be built on normal terminal strips. Never built KV level supplies before so a bit afraid of doing it wrong. I want the layout to be SAFE!

For the diode strings, will 2 diodes per leg be enough (2KV at 1A rating) or should I go higher?

John
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w9jsw
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« Reply #6 on: March 30, 2018, 11:06:36 AM »

Or, stay on the 811 mod design, and use the art-13 until I find a sweet S-22 or something similar.

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Todd, KA1KAQ
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« Reply #7 on: March 30, 2018, 11:08:18 AM »

Absolutely, John - you've come to the right place. As stated, no offense intended at all. I always ask a lot of questions because I don't know a fraction of what many of the guys on here know, and I hate to re-invent the wheel. I have a family and home, so my radio time is limited and precious.

Basically you want to make sure all the other components associated with the 813 or whatever tube are up to the increase in power. A simple analogy might be a car with a large engine but tiny, restrictive exhaust system. You can do a lot with an engine, but if it can't 'breathe' well, it won't reach its potential. Using a less restrictive exhaust system (larger diameter pipes, etc) helps to realize more power out.

So you want to make sure you're not arcing over in your tuning network, that chokes, transformers, caps and other components are up to the task. They're probably okay for some increase just as they sit. Clearly if Jack has swapped in the 810 for 813 and not had to change out everything downstream, at least some stock components will be fine.

I'm not well-versed in the ART-13, so I won't try to offer specifics. Others are bound to jump in with more suggestions.

But you're right - 50 watts carrier is okay for local, daytime stuff on 40 & 80m most days but at night? Good luck. Even 100 watts is difficult. If you've really been bitten by the AM bug you'll likely move beyond the ART-13 to something a bit more substantial before long. Many of us have several transmitters for different bands/conditions, from 100 watts to 'legal limit', whatever that means.
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w9jsw
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« Reply #8 on: March 30, 2018, 11:25:51 AM »

To be more clear, Jack started with an 811 and did fine at around 100-125 watts. This was his backup transmitter. He had a larger one that was 8000 modulated by 813. As an experiment, he swapped the 811 RF tube to a 810. He added a bias supply and a 1700v supply. This design was a bit evolutionary for a number of causes outlined on his radio page on his sight.

Sadly he recently has had a shack fire and all of his data has been lost. I have been communicating with him but it has been 11 years since much if this was built and not all of the "data" is crisp in the mind. This just makes it more fun to me. I am not looking for a cookbook. I want to understand the concepts and theory as well.

So, with all of your help I think I will stay on a 811 modulator and a 811 RF tube all on one supply. Perhaps I can ratchet back the modulator power a bit or still plan to use the reactor choke until I locate a better modulator. Hamfest season is upon us here with 2 in the next few weeks. I am getting enough parts from the 'bay to get started but am getting tired of all of the shipping costs to get them here to the shack.

John
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« Reply #9 on: March 30, 2018, 01:23:02 PM »

Try to find one of the old ARRL handbooks from the late sixties or seventies being they have lots of useful information on designing, building and troubleshooting high voltage vacuum tube circuits. They also have all the safety stuff too, not like the garbage in the handbook today. In all the handbooks from those decades there is at least one project using an 813 to build an amplifier or transmitter.  I would think if you want to do the tube high power thing thatís a good place to start, but thatís just me.


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KB2WIG
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« Reply #10 on: March 30, 2018, 04:06:31 PM »



Ray is hip, he knows what cooks.

This is a very good site.
                                  http://www.tubebooks.org/technical_books_online.htm

I particular, check this one out.
                                             http://www.tubebooks.org/Books/orr_radio.pdf

Its the right thing to do.

klc
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AJ1G
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« Reply #11 on: March 30, 2018, 05:14:44 PM »

Man, what a treasure trove of classic radio and electronic engineering references....

Thanks for the links!

Brings back memories of my having the copy of the '64 ARRL Handbook out on semi-perpetual loan from my high school library, and many squandered study halls there reading all of the other ARRL pubs that were part of the reference section and could not be checked out for loan, while listening to Frank Zappa and the Mothers of Invention on the multichannel music distribution system you could use with headphones there.
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Chris, AJ1G
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« Reply #12 on: March 30, 2018, 06:05:07 PM »


Don't apologize for your miss spent youth.

https://www.youtube.com/watch?v=1MewcnFl_6Y

klc
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w9jsw
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« Reply #13 on: March 30, 2018, 06:08:04 PM »

I would really like to find some sort of do's and don'ts for wiring practices on high voltage supplies. Things like how to do safe interconnect, how to route wires safely, how to feed HV thru the chassis, etc. For instance, I want to fire up a 2.5kv meter to watch the voltage. I suspect it is very bad practice to run the 1300 Volts voltage up to the meter in the open, and do the voltage divider there. So I am thinking of using a voltage divider under chassis, and then sending up 25V full scale and using a local dropping resistor on the meter that is calibrated for 200uA full scale at 25V. Things like that.

Already read one article about using HV solid core wire from Napa.

Also, what is the best practice for how to feed signals between the mod deck and the RF deck. Should the PS be on it's own deck. Stuff like that.

Perhaps I can find that in the treasure trove of documents listed above.

KLC - I am doing this for the children...and the cats. No unintentionally fried critters allowed...hihi. Especially me!

John
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« Reply #14 on: March 30, 2018, 06:43:01 PM »

I used many times RG58 for HV upto 5 kV  It is flexible and it is safe, an insulation leak gives a short to ground and blows the fuse.  Inside the cabinet you can use without shielding. Much more readily available than real HV cable
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w9jsw
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« Reply #15 on: March 30, 2018, 08:20:07 PM »

Frank Zappa ... Dynamo Hum ... Must have been thinking about the Art-13 generator?
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« Reply #16 on: March 30, 2018, 08:33:12 PM »



Watch this
http://slideplayer.com/slide/5731822/

Then  read/download these

http://www.ifwtech.co.uk/g3sek/in-prac/0901.pdf
http://www.ifwtech.co.uk/g3sek/in-prac/0902.pdf
http://www.ifwtech.co.uk/g3sek/in-prac/0903.pdf

As I always say when working around HV, Boom pa-chicka ca-boom boom boom chicka.

This should get you started.

klc
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WD5JKO
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« Reply #17 on: March 30, 2018, 08:36:13 PM »

 I have been watching this evolving topic. Quite interesting!

My 2 cents to add are that a hi mu triode like an 811 is not a great choice to be run class C plate modulated. Low to mid range Mu tubes seem to modulate better and to higher levels. I once tried a pair of 572B's in push pull with cross neutralizing. I could easily run 1KW DC input (2500v @ 400ma) and get somewhere shy of 700 watts RF out. The tubes ran pretty hot, and even when adding additional grid bias (lower conduction angle) for a given grid current, the benefit was little. My theory is you want a tube that will peg the plate current meter with zero bias. That rules out the 811 or 572B with a Mu of 160.

I later changed sockets and filament transformer, and tried some 805's. Those ran so much better, but are only rated for somewhere around 1500v. I eventually got brave (dumb perhaps), and raised the B+ in increments. Ended up running them at 2500V, 400ma, and about 850 out. The plates did not show any red. Used a quad of 808's in push pull parallel for modulators. Fair Radio Sales used to sell 808's for 75 cents apiece! Same thing with them...rated at 1500v again. I used 2250v, and that modulator made an easy 600 watts. I remember load testing it for hours....But that was almost 35 years ago. Memory is not perfect.

It is very fun to go these types of projects.

Jim
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« Reply #18 on: March 30, 2018, 08:50:13 PM »

I read all the posts,  I'm missing something, do you have an ART-13 or are going to build a xmtr from scratch??

The very first thing you need is a proper HV power supply.  That xfmr you keep mentioning is not going to do the job.  You need a HV xfmr that can produce 1200V-1500V DC and at least 300 ma.  A supply like that can power a 813 modulated by 811a's.  The 1N5408 diodes are fine but you need at least six diodes in each leg.  Only use a choke input filter, 8-10 hry and 20ufd cap at a minimum.  I always use a 470K resistor and a .01ufd 1KV ceramic cap across each diode.  Most folks will tell you that you don't need them but I always use them.  You can build the rectifier circuit using terminals strips BUT mount the strips on plastic above the metal chassis.

Another thing, stay away from UTC S series chokes. They're ok but probably the poorest of all the vintage chokes.  The UTC CG series chokes are much better, the earlier UTC PA series chokes are very good if you can find one.  Stancor or Thordarson chokes are good.  Thordarson made many different series chokes over the years.  The earlier ones are better than the later ones (the 21 series was the last and the poorest).  Stancor made pretty much the same chokes through out their history but the earlier ones had a lower HV voltage rating than the later ones that were potted even though they had the same part numbers.

You need to find a local ham that may have a lot of the correct parts you need and can part with them at a reasonable price.

Keep us informed of your progress

Fred

First thing, get the right power supply parts then work forward.
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« Reply #19 on: March 30, 2018, 08:50:46 PM »



Watch this
http://slideplayer.com/slide/5731822/

Then  read/download these

http://www.ifwtech.co.uk/g3sek/in-prac/0901.pdf
http://www.ifwtech.co.uk/g3sek/in-prac/0902.pdf
http://www.ifwtech.co.uk/g3sek/in-prac/0903.pdf

As I always say when working around HV, Boom pa-chicka ca-boom boom boom chicka.

This should get you started.

klc

Learn from an OLD HV technician. Bad HV technicians don't grow old..... Roll Eyes
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w9jsw
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« Reply #20 on: March 31, 2018, 08:13:27 AM »

I read all the posts,  I'm missing something, do you have an ART-13 or are going to build a xmtr from scratch??

The very first thing you need is a proper HV power supply.  That xfmr you keep mentioning is not going to do the job.  You need a HV xfmr that can produce 1200V-1500V DC and at least 300 ma.  A supply like that can power a 813 modulated by 811a's.  The 1N5408 diodes are fine but you need at least six diodes in each leg.  Only use a choke input filter, 8-10 hry and 20ufd cap at a minimum.  I always use a 470K resistor and a .01ufd 1KV ceramic cap across each diode.  Most folks will tell you that you don't need them but I always use them.  You can build the rectifier circuit using terminals strips BUT mount the strips on plastic above the metal chassis.

Another thing, stay away from UTC S series chokes. They're ok but probably the poorest of all the vintage chokes.  The UTC CG series chokes are much better, the earlier UTC PA series chokes are very good if you can find one.  Stancor or Thordarson chokes are good.  Thordarson made many different series chokes over the years.  The earlier ones are better than the later ones (the 21 series was the last and the poorest).  Stancor made pretty much the same chokes through out their history but the earlier ones had a lower HV voltage rating than the later ones that were potted even though they had the same part numbers.

You need to find a local ham that may have a lot of the correct parts you need and can part with them at a reasonable price.

Keep us informed of your progress

Fred

First thing, get the right power supply parts then work forward.

Yes, that is what I want to do - build a complete transmitter. I have purchased a modulator that was used in the ART-13. I do not have an ART-13 itself. Many have told me that this modulator is not a very good choice. I will be on the search for a better one but may use this one with a shunt reactor choke if I get that far by the time I run into a better modulator deal.

Yes, I want to start by building the power supply. I have a 1kw CT plate transformer to work with, as well as a 6.3v at 10A filament transformer for the mod pair. I was hoping I could get around 1300V at 250-300ma from it. There are no markings on it that tell me how much current it can supply. The ham I bought it from said it came out of a old transmitter. This same ham is helping me with some other parts as well.

Thank you so much for the specific information on searching for parts. This can be quite daunting to try to read decades of information and glean specifications from schematics that have only values listed. You have been quite helpful, Fred.

What I want to do is lay out the PS and then put a static load on it and see if the transformer can produce enough power without getting hot. I would use a variac to bring up the mains power slowly as I test it. Does that sound like a plan?

John
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w9jsw
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« Reply #21 on: March 31, 2018, 08:53:21 AM »

Jim Wd5JKO,

Thanks for the tube info. Very helpful. In the progression of this build, I plan to start the PS, then build the modulator. The RF tube is still a open issue, in my opinion. I guess I am struggling with "what works" vs. "what works well"...hihi

Do you happen to have a example schematic of a single 813 rf deck? I understand how the simple 811 triode works in the circuit but not clear on how the extra grids are wired on the 813 and how many different voltages are required. Also want to understand neutralization techniques. I have some air-gap neutralization caps on the way.

John
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w9jsw
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« Reply #22 on: March 31, 2018, 09:24:44 AM »

Power Supply Designer says this transformer can do 230ma at 1150 volts using a FW bridge and a 300uf cap, no choke, with a 5K ohm load. It calculated this from the RMS voltage and the resistance of the primary/secondary. I selected 5K assuming 1250v at 250ma. If I add the choke and the 20uf cap with same 5k load, I get 850V at 170ma. Not good.

Go looking for a new transformer? If so, what should I be looking for. PSUD says 1.5kv at .5A give me 1300VDC at 280ma using the LC circuit.

Why is the choke method better? Seems a lot more inefficient. What am I getting for this level of work - better regulation?

John
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w9jsw
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« Reply #23 on: March 31, 2018, 11:58:51 AM »

So, let's come at this from another direction.

If I use a capacitor only PS and get a reliable 1150vdc at 280 ma - what can I build? Using an 812 tube I estimate that it can put out around 120W of carrier at that voltage reading the data sheet. That gives me (according to W8JI's excellent information repository) a need for around 60W of full sine wave output from the modulator. If I assume that the 812 uses 130ma, I have 150ma or so of power for the modulator. Can I get it to use a pair of 807's? This would also be a good match for my ART-13 mod transformer rated at 50W.

Does this make sense? Recall that my initial goal was to build a transmitter between 100 and 200 watts with a lower HV supply. I did not want to go whole hog on a pair of 813's modulated by a pair of 811/13's. If I go shopping for a bigger transformer, then I am definitely heading away from my initial goals.

The next questions is whether a 120W transmitter is worth the effort. I am guessing that is a judgement that I will have to make. So far I am into this for around $150.

Maybe Borgi's K9YQQ recommendation to me of starting with a DX-100 or Valiant is not a bad suggestion at all!

John
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w9jsw
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« Reply #24 on: March 31, 2018, 12:17:25 PM »

Playing with PSU Designer, tried a voltage doubler circuit. It shows around 1840Vdc at 360ma. Can this be used? See attached...

* doubler-schem.pdf (17.2 KB - downloaded 19 times.)
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