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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 3234 times)
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KA3EKH
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« Reply #25 on: March 31, 2018, 12:42:36 PM »

Two things, old ARRL handbook on how and what to build if your going to build and start building with what you got, although there is a lot to be said for starting with something thatís already together. Building a high powered AM transmitter from scratch is no easy task. I have been doing this stuff forever both as a hobby and professionally for all my life and I would not attempt it. Way easier to find and adapt.

Learning starts with experience, ask ten hams how to do something and you will get twenty five different ideas. Itís a wise idea to ask direction but beyond a point too many cooks ruin the soup.
HV, high current or AC lines wonít hurt you if you treat them with respect and it sounds like you got the right idea. The old Handbooks have the method, its time to put it into practice. If you donít have everything you need start with what you got.
Software simulations are no substitute for solder. If you want to play with power supplies invest in some big 100 watt 100 K resistors and remember the one hand rule.

If this keeps up I will start my rant on analog VOM being far superior to the digital LCD next.



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w9jsw
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« Reply #26 on: March 31, 2018, 12:54:38 PM »

You may need to have that rant. I just looked and my digital vom only goes to 1kV. Wonder if an old trusty Simpson 260 can do any better...hihi

I played with adding the choke and got similar results. I think I will go build this and see what I can get.

Sorry about the series of back to back posts here. Kind of a stream of consciousness thread as I was exploring things on a rainy Saturday morning.

John

PS - wish I had paid more attention to this stuff back in the day when I was getting my EE degree. Back then, digital and micro-programming was the rage and that is the direction I went. Spent 35 years in operating system development and let my analog side get rusty. This is bringing a lot of it back.
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KA2DZT
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« Reply #27 on: March 31, 2018, 01:14:05 PM »

To get a good AM xmtr you need a solid HV supply.  You are not going to make it with that xfmr you have.  Forget the voltage doubler and the cap input filter.  You can only get so much VA from the xfmr.  When you use a cap input filter you must reduce the current load on the xfmr by about 30%.  You can build a nice xmtr with a supply at around 1000V-1200V and a current load of around 300 ma.

A single 813 modulated by 811a's is easy to build.  You'll get 100-120 watts out of it.  Both the PA and the modulator can run from the one supply.  You can use the ART-13 mod xfmr.  That mod xfmr can handle a lot more than 50 watts.

We can help you through every step of the build, but first find a better HV xfmr.

Also probably better to but away the power supply computer program.  I've been building power supplies for more than 50 years never needed a computer.

What other xfmrs, if any, do you have on hand??  I have a small collection of over 1000 xfmrs and chokes here.

Fred
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W2PFY
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« Reply #28 on: March 31, 2018, 01:17:46 PM »

Way back when I was in the US Army I acquired a ART-13 through MARS. I built a PS for it and had a lot of fun with it. One thing that was very noticeable was the talk back from the mod transformer. I was using a carbon mic, I think it was a T-17. T-17 mics come in two forms, one has only about 5 holes drilled in the cover over the microphone for high noise environments such as in a B-17 or a B-29. The other is exactly the same but has about a dozen holes drilled in the screw on cover. Perhaps this was for ground environments, to let more sound in? I guess if you have one of the 5 hole covers you could drill more holes in it for a better response?  Well anyhow attached is a recording of W2JBL's ART-13 mod transformer that is in his ARC-5 mobile rig. I know that his finals tubes are 1625's and I assume he is using the same tubes for his modulator since it is a 12 volt system?  1625's are the 12 volt equivalent of an 807 for those who don't know that. Chris has been using ART-13 mod transformers in quite a few home brew and modified ARC series transmitters and he produces excellent audio from them. If I were going to build a transmitter with said transformer, I would use the shunt form combination to keep DC off the secondary windings. I think I read somewhere that is you use this modified form with the heising modulation choke, you can get about three time the audio power through it, but as stated above, you may get talk back? If you do get talk back, the cure may be to add more inductance? It worked for me Grin Grin  Yes they are great transformers but you can't run 100 KW through it Cheesy Cheesy Cheesy      

* w2jblarc5.mp3 (1537.88 KB - downloaded 21 times.)
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KB2WIG
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« Reply #29 on: March 31, 2018, 01:19:25 PM »

Yes, yer 260 is OK. Its still being made and sold, so I guess its a solid design........

But......

   I got a GriefKit VTVM at a hamfest for $10.00. I have the rocket ship HV probe, so its a nice set up for the HV measuring follies. You cans till find these things at hamfests, cheep.

FWIW, I use a orange colored adapter for working on equipment.  This cuts down on the "Is it unplugged?". One should still check to see that the caps are discharged, and 'it' is not on, before poking yer fingers in it.  Take off the watch, ring if you made that mistake, so you don't have to try welding yer finger to that fil. supply.

 Looks like this,


* orange-ge-plugs-.jpg (70.81 KB, 1000x1000 - viewed 24 times.)
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W8ACR
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« Reply #30 on: March 31, 2018, 03:02:49 PM »

I have always thought that if the transformer has a center tap, it should be used as such.  If you have a transformer that is 1000VCT on the secondary, then it will give you somewhat less than 500VDC with a choke input filter. If you want to get, say, 1500vdc, then you either need a center tap transformer rated at about 3100VCT and use a choke input filter, or get a transformer rated at 1500VAC without center tap, and use a bridge rectifier and the filter design of your choice. The bleeder resistor will affect the output voltage as well. I like to use large variacs on the primary leads of my plate transformers. That way I can adjust the output dc voltage over a very large range. Unless you have access to a large stash of vintage parts, building a 1500V@300mA power supply is likely to be a fairly expensive endeavor. Transformers, chokes, and HV oil filter caps are getting expensive. Unfortunately, there arenít many shortcuts, at least ones that are safe.

Caveat: I have no formal training in electronic theory. These are my observations of 20 some years of building transmitters with some modest success, reading, experimenting, and on occasion, cheating death.  Shocked Be careful with high voltage equipment!

I have gravitated to using triodes for all my finals and modulators. This simplifies circuit design quite a bit. For the voltages that you have mentioned, I would recommend using 812Aís, 5514ís or 8005ís as finals. Of these, only the 812Aís are easy to find. There are many other tubes that you could use as well. The price that you pay for using triodes is the need for more driving power. I find this easier to deal with than adding a screen supply.

Good luck, Ron W8ACR
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w9jsw
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« Reply #31 on: March 31, 2018, 03:34:09 PM »

To get a good AM xmtr you need a solid HV supply.  You are not going to make it with that xfmr you have.  Forget the voltage doubler and the cap input filter.  You can only get so much VA from the xfmr.  When you use a cap input filter you must reduce the current load on the xfmr by about 30%.  You can build a nice xmtr with a supply at around 1000V-1200V and a current load of around 300 ma.

A single 813 modulated by 811a's is easy to build.  You'll get 100-120 watts out of it.  Both the PA and the modulator can run from the one supply.  You can use the ART-13 mod xfmr.  That mod xfmr can handle a lot more than 50 watts.

We can help you through every step of the build, but first find a better HV xfmr.

Also probably better to but away the power supply computer program.  I've been building power supplies for more than 50 years never needed a computer.

What other xfmrs, if any, do you have on hand??  I have a small collection of over 1000 xfmrs and chokes here.

Fred

Fred,

I have no other HV transformers here. What do I need to purchase? Can I buy one from you?

John

email on qrz if you prefer to take this discussion off-line.
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w9jsw
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« Reply #32 on: March 31, 2018, 03:46:59 PM »

Should I look at ICAS or CCS ratings. A Hammond 724 will to 339ma ICAS at 1500v, but only 226ma CCS. Price is not outrageous for a new transformer.

John
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KD6VXI
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« Reply #33 on: March 31, 2018, 03:47:56 PM »

A hundred watts carrier will do well on local circuits.

25 watts, and your in QSB hell, if mother nature isn't completely in your favor.

HOWEVER!!!

It's a lot easier to find a legal limit amp that will absorb 125 watts pep vs one that will take in a hundred watts carrier.

If you are looking at a hundred watts carrier, the next LOGICAL progression is a 3cx3000A7.

Otherwise, build the single 6146 and drive that into the legal limit amp of your choice.

At the end of the day, total watts drawn from the electric company ends up being about the same....  High level legal limit vs low level with amplification.


--Shane
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« Reply #34 on: March 31, 2018, 03:50:01 PM »

Should I look at ICAS or CCS ratings. A Hammond 724 will to 339ma ICAS at 1500v, but only 226ma CCS. Price is not outrageous for a new transformer.

John

I use the ccs rating as my carrier power level.  If your into 10 minute old buzzard xmissions, that's what you need.

If you follow that rule, the ICAS ratings tend to fall in line with the peak envelope power made at 100 to 125 pct modulation, give or take.

--Shane
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KA2DZT
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« Reply #35 on: March 31, 2018, 10:07:00 PM »

What is the DC resistance of your xfmr's secondary winding.  Measure the whole winding,  let me know.

Fred
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w9jsw
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« Reply #36 on: April 01, 2018, 07:37:50 AM »

88.7 ohms
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w9jsw
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« Reply #37 on: April 01, 2018, 08:45:03 AM »

Fred,

Are these the specs we are going to follow with the 813 RF tube? Will the PS have to also provide 300V and -160 volts (or close to that) given that we will be at 1100-1150 instead of 1250. Just trying to follow along...

John


* 813-plate-modulated-specs.JPG (144.57 KB, 608x592 - viewed 34 times.)
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KA2DZT
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« Reply #38 on: April 01, 2018, 11:37:57 AM »

John,

The screen (G2) voltage just comes from the plate HV supply.  The screen is modulated from the modulated plate voltage through the screen dropping resistor (very simple).  Look at the specs, it tells you what the screen resistor should be.  Anything close to that 27K will work.  Wattage has to be calculated but probably 50-100 watt resistor.

The grid (G1) voltage is developed from the grid drive power through the grid resistor.  Look at the specs, it tells you what value grid resistor to use.
The grid voltage can also be developed from a combination of (-) fixed bias voltage and a grid resistor.  The value of that resistor (using some fixed bias) can be calculated.  I know you're a computer expert, so, if you forgot Ohm's law we can help you with that (Hi Hi).

If you don't use any fixed grid bias then you need to include a clamp tube circuit on the PA screen voltage (clamp tube 6Y6). Again, this is also very simple to do.

Fred

I'll add some more HV power supply suggestions later today.
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w9jsw
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« Reply #39 on: April 02, 2018, 08:09:46 AM »

Here is what I have so far for a 813 design. I have pulled quite a bit from the K1JJ 813 x 813 design. Goal is to use heavy build techniques that can allow for a later addition of a second 813 and a separate larger RF power supply. I have not done much on the power supply, Fred. Awaiting your suggestions.

John

* 813 Transmitter v0.1.pdf (110.92 KB - downloaded 16 times.)
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KA2DZT
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« Reply #40 on: April 02, 2018, 01:21:39 PM »

John

Can you put up a few pics of the xfmr you have??  Are there any numbers on the xfmr??

Fred
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w9jsw
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« Reply #41 on: April 02, 2018, 02:23:38 PM »

Says TP-189. Here is the eBay item. Not at home right now. Let me know if it doesn't work.

https://www.ebay.com/itm/Vintage-Power-Plate-Transformer-for-Vacuum-Tube-Transmitting-Equipment-1KVct-/173201342202
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w9jsw
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« Reply #42 on: April 02, 2018, 04:04:40 PM »

Don't know what you are thinking Fred, but I was comparing the 2 datasheets for the 811 and 813. We could use this trans for the modulator only at around 750v CCS. The sheet says that is good for around 175 watts. Then we could run the 813 higher, say around 1800 or so to get 250 watts of carrier. Would the ART-13 modulator handle that much modulation?

John
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KA2DZT
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« Reply #43 on: April 02, 2018, 04:04:53 PM »

John

I took a good look at the xfmr.  Seller probably has the current load about right (200ma)  I don't recognize the part number but I"ll check some stuff later today.  Trying to see if the xfmr can be used in some capacity for your xmtr project.  I'll explain more later, have to run some errands right now.

Fred
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w9jsw
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« Reply #44 on: April 02, 2018, 05:10:05 PM »

Knowing what I know now, I would have never bought it. I put a minimum bid on it and forgot, and it won. So no biggie if we decide to not use it. The good thing is if we use it, we can then buy a cheaper second supply that does not have to give us 400ma or more. Best new 1500V trans I can find is the Ameritron one that is used in the AL-811. $105 bucks. Diodes are cheap. Caps are not that bad either. Whatever you suggest. I am flexible.
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KB2WIG
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« Reply #45 on: April 02, 2018, 05:29:39 PM »



You could always put a want add in the wanted section.........

KLC
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KA2DZT
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« Reply #46 on: April 02, 2018, 11:06:40 PM »

John

Looked through over 10 pages of xfmrs on ebay.  Didn't see anything that looked good.

Have to try some other sites

Fred
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« Reply #47 on: April 03, 2018, 03:32:13 AM »

John,
        If you are looking to achieve an output of roughly 100w, why not just acquire a Viking II or DX-100? You can learn a lot about transmitters bringing a commercially built (or kit built) rig back up to speed while building your parts list for a big homebrew transmitter. IMHO, anything less than a pair of 812's modded by a pair of 811A's would probably be a little bit of a letdown for a "first project". For that first 100 watter, about 100-200 dollars for a complete rig with good bones, change some caps, clean some contacts, etc., learn during the process, and get to some "on air" time fairly quickly. Consider the approach.

Just my 2 cents worth...

Phil
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w9jsw
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« Reply #48 on: April 03, 2018, 08:43:41 AM »

Thanks Phil,

That has been suggested by others and is probably a sound suggestion. Just not my way. I would rather spend more time and money building something of my own hands rather than spending time cleaning dust and grime off of an old xmitter. Just how I choose to spend my time. If you look at my qrz page you will see the SDR that I built. That is my only radio. I glean much satisfaction from a homebuilt unit. I thought about building a solid state linear for it but when you get into all the complexity of the supporting circuitry,  it actually is a bit simpler to build a tube rig. Plus way more fun, IMO.

The AM bug has bitten me. I spend almost no time on slopbucket mode. Did some digital for a while but that seems so automated.

I am building this rig robust enough to allow me to add a second 813 later so this first radio is just a stop on the journey, not an end point. A guy has to keep busy in his retirement, right?

John
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« Reply #49 on: April 03, 2018, 08:46:26 AM »

Fred,

This transformer is still avail on eham. An old navy transformer. Trying to get some specs for it. Looks like a beast! Probably cost more to ship it than it is worth, however. It's located in Tom's River, NJ WA2JHS, not to far from your QTH.

John


* image1.jpeg (4871.42 KB, 4160x3120 - viewed 98 times.)
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