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class H modulator




 
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SV1SPW
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« on: October 17, 2020, 02:53:55 PM »

Hi everyone, i am interested in building this class H modulator : http://www.classeradio.com/classh.htm.
Have expirience with high voltage tube gear and basic understanding of solid state audio amps, construction expirience in this regard is rather limited.
I find the concept of class H very interesting, i would like to try it mainly for educational purposes.

Problem is i have not worked with the kind of bipolars used, so i cannot tell if they are going to operate properly with my 96 volt supply. Power is not an issue, carrier  to modulate will be no more than 200 watts.
Is the supply voltage adequate? I think i will not need more than 3-4 devices per leg (6-8 total BJTs and Fets).
Any help would be greatly apreciated,
greetings from Athens, Greece
Konstantinos
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vk3alk
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« Reply #1 on: October 17, 2020, 10:50:44 PM »

Hi Konstantinos...

Steve is the one to give more accurate advise on this circuit although are fairly sure it's OK ....
There was a more simple one I think but cannot find the circuit...

You would have to use the power supply voltages or close to it as per the circuit diagram 125VDC and 63VDC.... and would advise you to use the shutdown bit as well.... if you get a short across your modulator many components will go bang !!!!!!!

For a 200 watt carrier TX 3-4 devices per leg should be Ok ..... maybe a fan would help but the heat generated will guide you there...

With this type of Modulator give attention to the efficiency of your TX module as the modulator has to deal with everything and does get HOT ......

Its not the easiest build ...... quite a bit really and construction as well .....

Do you have a 746011 chip ?

The audio quality should be great also ....... I use one in my 40M Transmitter but wouldn't advise building the one I use...


Wayne




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SV1SPW
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« Reply #2 on: October 19, 2020, 12:33:47 PM »

Thanks a lot Wayne for the comments. I think i should run a spice sim first to get an idea how it works. No, i don't have the 746011, as they seem hard to find. I 'll take one of the ordinary types and use additional circuicitry to make it behave like the aforementioned.
I shall write about the progress -or not- i make.
Konstantinos
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vk3alk
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« Reply #3 on: October 19, 2020, 07:01:17 PM »

Running a spice sim would be a good idea and would show information on how it works.....and you could go forward from there....

If what your doing is a bit of fun and learning I have somewhere more simple circuits that would be easier to build and learn from etc:



Wayne
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steve_qix
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« Reply #4 on: October 29, 2020, 04:19:58 PM »

Hmm... I would not recommend building that modulator (and I designed it  Wink ).

Why do you want to use class H at all ?  The pulse width modulators work much better, and are smaller, more efficient and have considerably lower power supply requirements.

I came up with that design to correct an issue caused by the reverse transfer capacitance (Miller capacitance) of MOSFET devices if used in the lower rail of the class H modulator.

Since then, I came up with a design that uses MOSFETs everywhere, and fixes the artifacts previously caused by the Miller capacitance of the lower group of devices.  I built a prototype to prove the design, and it worked as expected.  However, I never created any documentation for the design, and would have to reverse engineer the values I used in the circuit  Embarrassed .

My recommendation would be to use PWM unless there is some really good reason not to  Cheesy

Regards,  Steve
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High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
vk3alk
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« Reply #5 on: October 29, 2020, 06:10:49 PM »

I think this is the circuit......
From memory a guy did build it .... a K call not sure ......

Also uploaded my 40M one that looks a mess but having said that sounds great but does get hot....
Will never build another one just not worth it ....


Wayne





* easy_class_h_rev_b.jpg (204.07 KB, 920x714 - viewed 21 times.)

* Class H CMCD.JPG (465.97 KB, 1600x1200 - viewed 21 times.)
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K6JEK
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RF in the shack


« Reply #6 on: Today at 01:35:47 AM »

Hmm... I would not recommend building that modulator (and I designed it  Wink ).

Why do you want to use class H at all ?  The pulse width modulators work much better, and are smaller, more efficient and have considerably lower power supply requirements.

...
My recommendation would be to use PWM unless there is some really good reason not to  Cheesy

Regards,  Steve
I built and still use that design of Steve's. I built some PWMs since so I know Steve is obviously right. But it's a conversation starter. Many years ago I built this modulator and a class E RF deck and on the urging of my friend Rod, KQ6F, took it to a little Hamvention in Monterey. He brought along his PWM with a class D RF deck with PC user interface rig. In 2004, pretty hot stuff, don't you think? No one gave a damn about Rod's stuff. But they ooh and ahed over the H + E. I'm pretty sure it was the meters, the lights, the big heat sinks and all that  aluminum that wowed them.

Back then I could give a pretty good description of how all this works even though I could never have designed it.  Now I just tune it up and use it. It's sounds like a million bucks but then again so does Rod's latest  PWM D + D/E RF and he can lift it with one hand. (BTW I still don't know what he means by D/E RF deck)
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vk3alk
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« Reply #7 on: Today at 02:01:00 AM »

Hi Jon...

Not sure if that's your name....
Very good on the Class H modulator and its still going which is even better.....
Maybe you could post a photo ?

What carrier level does it run.....
Mine sounds amazingly good so will stay in use ..... I don't want to retire it at all enough though are building another TX...

Rods TX .... I did build it and posted a photo on the Forum went very well but it looks VMCD and not Class E to me ....
The waveforms look similar etc:


Wayne
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