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Mod iron for Class E




 
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KC1DPM
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« on: June 22, 2021, 05:16:35 PM »

I fell down the Class E radio rabbit hole, and am starting to piece together components for a transmitter. A simple explanation of my idea is to series-modulate class E finals with a solid state audio amplifier, as I already have one. The transmitter design is based off WA1QIX's 8-FET, ~400 watt project: http://www.classeradio.com/8_fet.htm

I intend to use the PA amp driving a mod. xfr in place of the pulse width modulator, but I'm having trouble finding a transformer that will do the job. I did not grow up tinkering with tubes, and thus am quickly realizing that the high-voltage-but-low-current ratings of the secondary windings on most available mod. xfrs may mean this idea is dead in the water. What I believe I need is a low impedance 1:1 transformer, good for the AF range.

Am I approaching this wrong? Is the PWM'er the only reasonable way to provide high-current modulated DC to the finals? At this juncture, it's only right for me to come clean and say I have never built an amplifier before, but I'm well versed in electrical safety, am eager to learn and willing to listen.

Thanks all,

-Patrick
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kb3ouk
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« Reply #1 on: June 22, 2021, 06:43:19 PM »

Read this thread. http://amfone.net/Amforum/index.php?topic=30798.0
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M0VRF
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« Reply #2 on: June 23, 2021, 02:11:34 AM »

Seems such a waste!

I can send you a modulator.

You'll have to supply your own FETs and filter components + large electrolytic across the HT supply.

The PCB needs 12V to run and will mod any HT up to 500V+

JB
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N4LTA
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« Reply #3 on: June 23, 2021, 06:19:20 PM »

I agree. It is a total waste of energy. A PWM modulator is simple and delivers broadcast quality audio. Using a transformer may work, but way more work and not likely the quality.

I have a board you can have also. M0VRF has it all on one board.

Pat
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vk3alk
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« Reply #4 on: June 24, 2021, 01:01:34 AM »

Hi Patrick...

There are definite advantages using a PWM apart from great audio quality....

If you use a Half Bridge design its a small little board and has high efficiency so heatsinking is minimal....
Only one HV Power Supply is required .... say 150 volts @ 4 Amps depending on your power level....
There is no negative over modulation issues like when you use Modulation Transformers....
If you over modulate it only cuts off the Drain Current and no large voltage spikes occur etc:  ....
If your going to use Power Levels over 500 watts then maybe Steves Class D design would be better or simpler way to go...

A nice Transmitter would be Rods 75M Class D using a LPF in the output and a Modulator like JH or Pat suggested ....
It would all fit into one reasonably small box too....

Just some thoughts..  Smiley


Wayne
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w9jsw
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« Reply #5 on: June 24, 2021, 11:35:54 AM »

Where can I find Rods schematic or an article on such.

JB - do you have any details on your 1 board design?

John

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M0VRF
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« Reply #6 on: June 24, 2021, 12:47:57 PM »

Check;

350W 3 band Class D FET AM Transmitter

2nd page.

Fairly standard stuff.

I really have no idea why anyone would contemplate not using PWM as it's so simple.

The design is similar to the schematic Nigel posted up some time ago, always good to design a PCB as it makes things so simple, it's all SMT and about 1"sq.

Regards.

JB.
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KQ6F
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« Reply #7 on: June 24, 2021, 02:00:06 PM »

Where can I find Rods schematic or an article on such.

JB - do you have any details on your 1 board design?

John



I'm Rod.  Here's my PA schematic.  Also am attaching my modulator schematic although it's 5 years old and uses older thru-hole parts.  Other modulators mentioned in this thread use newer parts.

If I had to do it again I'd use 900-volt FETs from CREE.  They weren't available 5 years ago.


* ClassD_E PA.jpg (114.33 KB, 1000x755 - viewed 196 times.)

* ClassD_E modul.jpg (118.05 KB, 1000x583 - viewed 200 times.)
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M0VRF
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« Reply #8 on: June 24, 2021, 03:14:59 PM »

Indeed Cree C3 FETs and the drivers can be NCP81074A's.

The modulator is nice and the UCC part can be replaced with the Silabs part as can the half bridge driver as I have done with my latest design. However there's no need to if you're a fan of using old parts (seems to be the way on here) and as they (the old ones!) have been around for ever I guess they still will be for a while. You hardly need cutting edge tech in this application anyway!

By using the latest parts cost and complexity are reduced but it means nought!

I've offered PCBs on here before and got next to zero (1 actually) interest.

I'll always build the smallest and most modern design I can just for grins. Power wise 200W (wi 96V) is more than enough whilst 100W is legal (UK Ham) and safe (can use 48V).

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ka1tdq
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I make stuff


« Reply #9 on: June 24, 2021, 10:13:36 PM »

I've run modified Heising for class E transmitters from the 50 watt to 400 watt carrier level successfully and the audio quality is amazing. You can't beat the simplicity. Don't throw the baby out with the bath water.

Jon
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KD6VXI
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« Reply #10 on: June 25, 2021, 09:41:29 PM »

I've run modified Heising for class E transmitters from the 50 watt to 400 watt carrier level successfully and the audio quality is amazing. You can't beat the simplicity. Don't throw the baby out with the bath water.

Jon

Modified heising is great.

However, for an evening and 20 to 25 bucks in parts you can have better.

For half to three quarters the price of the audio amp I can have a pulse width modulator built and running.  And I don't need a heising choke (more money) or the coupling csp (more money).

Heising was great.  Decades ago.

Couple the DC to the drain and you have 100 pct control of the waveform.

My PWM will pass 400 plus pct positive peaks.  Show me heising that will do that.

Theres a reason peoe have been trying to get you to build a PW modulator for years, Jon.

Not to down anything you've built.  Technology marched in.

--Shane
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ka1tdq
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« Reply #11 on: June 25, 2021, 10:13:38 PM »

As long as something gets built, I donít care one way or the other. I prefer the large monstrosity components. Some people drive Ď57 Chevys too. Good for them. Do what makes you happy.

Jon
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M0VRF
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« Reply #12 on: June 26, 2021, 03:17:38 AM »

I figured it was a USA thing, overuse of natural resources, especially iron! and everything built Massive!

I jest of course and understand that if it works for you why change it?

However for me I like to make things small so SMT and modern tech is my thing + I sell commercially.

You can lay out a PWM board that has all the components less the switching FETs and LPF that's <1"sq, adjustable deadtime, dc-dc so it will run from 18-75V, incredibly simple.

Whatever 'Floats your boat'

JB.
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