PA-47 at High Power !

The little Class "C" PA-47 RF Power Amplifier has grown up, I have doubled the original output of 4.7 Watts, to greater than 14 Watts.

PA-47 Ready for Modification
The new FET Leads will be bent
to Accommodate the Existing PCB Holes

I have replaced the general purpose IRF510 Power FET with an actual Special Purpose RD15HVF1 HF Power FET (from RFParts), and then connected the PA to a large stable DC Supply (Battery).

The results at full power, are;

• With a 12.51 Volts DC supply running at 2050 ma (25.7 Watts DC Input with FAN)
• Exciter provides 12 mWatts Input at 10.140MHz
• The PA-47 output is 75 Volts PP RF measured at a 50 Ohm Load, which is: 14.1 Watts
• The HeatSink Temperature at the FET raised about 20 degree to 94.7 Deg F

This is a gain of 30.70dB and a Efficiency of about 66%.

I am a real Happy Camper !

Note: this is a very small 1 x 1.5 inch PCB, with a large CPU HeatSink.

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I plan to re-layout the PCB to accommodate a Fan Control circuit and correct the small layout errors as explained on previous posts.


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Destructive Testing of PA-47

Late last night before leaving my Shop, I inadvertently put a 12.6 Volt supply plug onto the 1 Watt PA, which was designed for only 9 Volts (see previous post). The results was a toasted 2N7000, but that is NOT really a problem, as I have replacement parts (and boards).

PA-47-1 and PS-47-5

Later in bed, and while trying to fall asleep, I got to thinking; Why not do some Deliberate Destructive Testing while recording circuit parameters? I could think of several scenarios that would be fun to try.

And besides, how often do you get to deliberately abuse two of your favorite RF Power Amplifiers?

Some Abuse Comes to Mind:

• Put an over-voltage on the supply connector (similar to the mistake above).
• Run the PA at the over-voltage condition while cooling the FET with Freon.
• Create maximum VSWR at the PA output with a shorted and open coax (this may have to wait for another day) 

For the tests, several FETs were prepped from randomly selected Volunteers. Each was outfitted with an attached HeatSink. The HeatSink is a 1 inch square piece aluminium flashing, super-glued to the FET.

Preparation for Expected Failures

Initial Normal Use - Base Line Tests

Input to the amplifiers is provided by my Propeller microprocessor system, which supplies about 12mWatts into the amps (see previous posts).

PA-47-1, A one Watt PA, with Normal DC Supply Voltage

• Power Off - HeatSink at 75.7F
• 9.1 Volts DC, RF input Off, 41 ma, HeatSink at 82.4F
• 8.8 Volts DC, RF input On, 250 ma, HeatSink at 103.6F => 20 Volts PP at 50 Ohm Load => 1 Watt

PA-47-5, A Five Watt PA, with Normal DC Supply Voltage

• Power Off - HeatSink at 73.4F
• Fan Off, 12.1 Volts DC, RF input Off, 90 ma, HeatSink at 82.9F
• Fan On, 12.1 Volts DC, RF input Off, 270 ma, HeatSink at 73.8F
• Fan On, 11.5 Volts DC, RF input On, 1170 ma, HeatSink at 102.9F => 42 Volts PP at 50 Ohm Load => 4.4 Watts

PA Input (lower) and Output (upper)
Output is 4.4 Watts
5 Volts Per Div

Destructive Tests

PA-47-1, A one Watt PA, with Over Voltage Supply - Rated at 12.5V at 1200 ma

• Power Off - HeatSink at 75.7F
• 12.1 Volts DC, RF input Off, 80 ma, HeatSink at 84,9F
• 11.8 Volts DC, RF input On, 710 ma, HeatSink at -25.3F with Freon => 30 Volts PP at 50 Ohm Load
• 11.8 Volts DC, RF input On, 520 ma, HeatSink at 148.6F without Freon => 25 Volts PP at 50 Ohm Load
• Output Transformer was Hot to touch.
• Only the FET Failed 40 seconds after Freon was removal, afterwards maintained 145F while power was applied - FET was toast!

PA-47-5, A five Watt PA, with Over Voltage Supply - Rated at 31.5V at 3170ma

• Power Off - HeatSink at 73.4F
• Fan connected to a separate 12 Volts DC Supply
• Fan On, 30.19 Volts DC, RF input Off - The FET and the two drive (Sziklai) transistors Failed within 3 seconds of DC voltage being applied.

End of Destructive Testing

The Dead Soldiers

Several FETs were used to collect this data, only a condensed synopsis is provided above.

Conclusion

The PA-47 Circuit boards survived much better than I would have had imagined, components failed long before the PCB traces. For Higher Power PA's more design aspects need to be understood and considered.

The two PA circuits have be restored to there former condition, awaiting further tests or use.

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Destructive Testing - Epilogue :-)

For the above described Destructive Tests, all intentionally destroyed FETs were randomly selected Volunteers (RIP). They are well preserved and available for additional photos and future forensic examinations.

Although mildly inconvenienced, no Electrons were Captured, Created or Destroyed as part of these experiments, they were ALL returned to their point of origin.

Almost all (well, maybe some) of the released Magic Blue Smoke was captured or contained for return to the part manufacture, if desired.

All transferred RF energy was absorbed by the 50 Ohm Load, most of it was emitted as therms and dissipated into the surrounding area. Only a small fraction of RF energy was transferred to a local Receiver where is was used to monitor the testing progress.

Only Ozone Depletion-Free R-134 Freon was used for the cryogenics phase of these tests.

With some microscopic surgery, all Causalities were fixed, repaired, or replaced. Both boards have fully recovered and will be returned to original service.

All of this was in the name of; Science, Ham Radio, and/or just plain FUN :-)

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PA-47 At Only 1 Watt

Original PA-47
with Large Heat Sink, 
Matching Transformer
and FET IRF510

In keeping with my goal of making my Homebrew projects as small as my abilities allow and using the same previously created PCB board (see previous post on my PA-47 Power Amplifier)

I have reduced the size of the output matching transformer and changed the output FET from a IRF510 (TO-220) to a 2N7000 (TO-92).

New PA-47  Running at
1 Watt Output

Knowing that the 2N7000 would not produce the same 4.7 Watts of the replaced IRF510 with its large heat sink, I planned to reduce the supply voltage; from 12.6 Volt down to 9 Volts, and reduce the size and turns ratio of the matching transformer form 1:3 to 1:2.

New Replacement Parts
of the Original PA-47
are the 2N7000 and 
Smaller Matching Transformer

Initial test produced 1 Watt RF output, and a Very Hot 2N7000 FET. A small 3/4 inch sq piece of aluminum flashing was super-glued to the FET which solved the heat build-up problem. Just in case, I also installed a pin socket for each leg of the FET (which means I can easily replace the FET, if I inadvertently cause it to release its Magic Blue Smoke :-).

For this first test, the DC input was 8.5 Volts (not a very fresh battery set) at 360 mAmps: or 3.06 Watts DC Input, which suggests the PA at only about 32% efficient (more work is maybe needed to increase this). The standby current (no RF input) is about 13 mAmps, and most of that is used to drive the green Power-On LED.

30 Meter Low Pass Filter

Without the FAN and Large Heatsink that was used in the initial PA-47, this PA is silent.

Like the original PA-47 an outboard Low Pass Filter is necessary and was used for this experiment.

TR Relay Mounted Under the PCB

The yellow-tag jumper on the header turns on the TR Relay, which is mounted on the under side of the PCB. Normally transmitter control from the exciter would be connected to this header.

The RF voltage measured at the 50 Ohm Load via the scope: 20 Volts PP, (20/2*.707)^2/50 => 1 Watt, or as per the web  RF calculator.

This smaller and lower power PA will be perfect for my ongoing Propeller 30 Meter Beacon efforts.

After I correct the PCB layout (see previous discovered errors),  and if there is interest, I may make the PA-47  board available, or as a complete Kit (but, as a board or kit, this would not be suited for first time builders, nor a builder without a Microscope).

The Exciter (Driver)

The Exciter
Outputs 12 mWatts

For this experiments and as explained previously, I used my Propeller Transmitter as the exciter which provides 12 mWatts of drive. The Propeller is the second board in the stack.

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CNC - Projects

I know this post is not about Ham Radio, but . . .

At Jack's Homebrew Meeting
Jack, Bob and Walt

One of the many topic of discussion at Jack's Homebrew Club meetings last night, one was his Homebrew CNC project. He has used his CNC to cut Wing Tip molds for a Boeing Aviation Restoration project.

Also, I have been discussing and following John Hoaglun progress of his recently acquired CNC PCB Router. John has done some interesting experiments to create configurations that allow for detailed routed PCB projects.

All of this has rekindled my interest in my own, all most completed (75%) Homebrew CNC Plywood Router project - which I named the "M45".

M45 has been standing in the corner of the shop for several year, gathering a little rust, waiting for the right moment to be reactivated. If I remember correctly, the bed was designed to hold a 4 x 8 foot sheet of plywood, with an active routing space of 4 x 5 feet.

All of the parts for M45 were cut on my PlasmaCam CNC Cutter, Welded together, Milled, or folded in my shop. Motors, Transformers and some other Electronics were purchased from Surplus Center. The actual motor controllers are from Geokodrive. I added my own designed positions encoders to the motors.

The X and Y feed motors are quite heavy duty DC motors, I do not remember the spec's. They are about 4.5 inch diameter, about 8 inches long, and with a 5/8 inch shaft.

Y-Axes Motor and Drive Chain

X-Axes Motor and Drive Chain

The Z feed motor is smaller, with an internal encoder. This part of the project needs some rework to center the feed screw on the vertical carriage.

Z-Axes Motor (with internal encoder)
and Drive Belt

The Y gantry rolls on bearings at each end of the slide, and attached to a self tension Chain and Cable. An under slide bearing provide stability.

Y-Axes Drive Chain and Pulley

Y-Axes Rail

The Chain and Cable are self tensioned, the carriage attaches with a single bolt (one each side). The other rail looks the same.

Y-Axes Chain  and Cable Attachment

Under Slide Bearing
Tension is provide via the bolts on the ends

The Controller uses three Geckodrive Motor Controllers as seen on the left, the Power Supply and Transformers as mounted on the bottom. Four sets of Transformers and two sets of Rectifiers are paralleled to supply voltage to the large filter Cap. Rectifiers are mounted low on the front (right side), Controls and Switches upper right.

CNC Controller and Power Supply

Fuses and individual motor controls (i.e., On/Off and Jog) switches and status lights are on the front.

CNC Controller

Some un-used parts :-)

Un-used Motors
These were tried, but too small for this Project
They maybe used for another CNC project

About the only things that are missing to complete the M45 project are; the Wiring Harness, the Vacuum System, and some rework on the Vertical Feed. Note: This project was started long before I knew much about CNC.

As shown the Motors are mounted, and the Controller has been built and tested. The project was put on hold for a variate of competing interests and responsibilities.

I should complete this Project.

But alas,  . . .  I have too many projects, and too little time (now that I am retired :-)  to (re)start work on another project

I wonder, . . . How did I ever get anything done when I was still working a 60 hour per week job???


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PCB/Vinyl Cutter

Hey, I just saw a Great Post and Idea on the "Homebrew_PCB" yahoo list by Richard D.

I want to capture the idea here for my later reference.

It is a Roberts Quik-Cut Vinyl Tile Cutter that can be used to cut PCB material

It can be found at Home Depot

• Model # 30002
• Store SKU # 729019
• Price: $50

I will have to try one of these.

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PCB Solder Jumpers - Cont'd

With the success of my previous PA-47 project, I feel like blogging again.

Previously, I proposed a Solder Jumper Pad Footprint for my future projects (see previous post). One of those was used on the PA-47 Amplifier. The manufacture did not have any problems creating the pads, as shown.

Solder Jumper - 0703

The overlapping hooks of the jumper pattern makes for easy filling with solder, and then with some Solder Wick, it was just as easy to re-open.

Solder Jumper - with Solder

I may need to create a larger jumper pad set for larger traces, as shown the traces between pads are 16 mils. For reference, the copper pour ground grid is made with 6 mil traces.

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A Personal Note: This post is a milestone for me, it is my 100th post for the year, which is more than any previous year, and far more than I would have expected when I started in 2009.

I suggest everyone start a Blog. It is very enjoyable and you will meet and network with many interesting people. I would also suggest you encourage your kids to blog (ether privately or publicly) about topics that interest them. Kids with learning-disabilities should start ASAP, even if they only write one line of text each day - they WILL see progress. Because they will blog about topics of their interest, and because they are the expert of their activities, it will be an easy task. They may not be a potential Doogie Howsers, but blogging will help collect ones thoughts. In the TV show plot, Doogie was a great Blogger.

Actually, my blogs are not for me, not for you, nor any of my current readers, my blogs are for my Great-Great-Grand-Children - it is a way to communicate with them of my ideas, interests, and thoughts. I would have loved to have found letters (or blogs) written by my Grand Parents, or their Parents.   Sadly, I only know the names of six generations of Fathers, and very little else.

Do your part - Create a Blog!

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PA-47 - A QRP KiloWatt

I have not posted anything for the last few weeks, I have been a little bummed out.  I started work on an interesting Project, which is a "QRP KiloWatt", a 5 Watt Amplifier. It will be used with my Propeller Beacon Project (see many previous posts) and maybe my other QRP projects.

Sziklai Pair

What renewed my interest in building yet another PA, was a new (new to me) configuration of transistors - called a "Sziklai Pair", or sometimes referred to as a "Complementary Darlington". The configuration is actually quite old, and was invented by George C Sziklai  (pronounced as: "SICK-LIE", which is the best guess as per the web). I had not seen or used the configuration before.

To me, the interesting spec is that the Sziklai Pair can produce nearly Rail-to-Rail output voltage - which is exactly what is needed for a FET PA driver. FET PA's require high signal voltages (i.e., +6 or 7 volts to drive the gate) which is much more than the typical 0.6 volts for a normal transistor. Transformers can be used to produce the high drive voltages for FET PA's. But, I did not want to do that, especially if two simple transistors can do the task. I have built PAs before and always had messy drive circuits and problems.

I configured my planned Sziklai Pair Driver and FET circuit within LtSpice. It took a while to get the configuration and front-end bias right for my desired "class C" operation. But in the end, it is much simpler than I had imagined. Resulting in a circuit with very few components. LtSpice suggested I should get about 4.7 Watts at 10.140MHz from 12.6V DC when driven from my Propeller (Prop) Beacon, The Prop only provides about 2.5 P-P Volts at its output pin (or only about 12 mWatts drive).

Excitedly, I transferred the LtSpice configuration into DipTrace Schematic Capture, and from there created a DipTrace PCB layout. The circuit includes; SOT-23 2N3904 and 2N2906 for the Sziklai Pair, a IRF510 for the PA (standing up to mount to a heat sink) and a TR Relay and its support circuit. As usual, I wanted the circuit board to be as small as my abilities allow. The PCB was going to be only 1.5 x 1.0 inches, using SOT's and mostly 0603 parts.

While designing the circuit, I noticed that I had used mostly "47" valued parts, for example 4.7K resistors and 47nF capacitors. And, therefore I decided to name my new QRP KiloWatt - the "PA-47". Just for fun, and with very little work, I was able to convert all parts to 47 values. Besides, LtSpice said it would produce about 4.7 Watts - so what else could I name it?!!

The circuit was so simple I decided NOT to try to breadboard it, I just quickly pressed the DipTrace button and ordered the PCB's (that is way too easy).

For about a week and half, I waited for the PCB's to return from the Manufacture.

PA-47 - PCBs as Received

PA-47 - PCB Under the Microscope

Finally, the PCB's arrived, I excitedly loaded a board. But - DANG!! - I noticed I had used the wrong SOT foot print for the two Sziklai Pair transistors!! Maybe I pressed the DipTrace Order button too soon (the button is just too easy and handy). The two driver transistor's Emitter and Bases were exchanged on the PCB - DARN, DARN and DANG!

2N3904 SOT-23
as  MMBT3904

OK, now what, . . . . if I turn the transistors up-side-down, "dead bug style", the PCB foot print would work. All I had to do was bend the legs up and then try to solder the SOT transistors up-side-down on to the PCB. I notices the leads almost broke off when bending them back that far. I planned to fill the little crack with solder as part of the installation process, it would only require a slightly larger glob  of solder on the pin (actually the glob of solder is about the size of a flyspeck and can only be seen under the Microscope).


For the initial tests, I would not install the parts for the TR Relay Circuit, as it was not really necessary (I just shorted two pairs of the pads together, as if the Relay was always on).

PA-47 - Mounted to a CPU HeatSink
Output Matching Transformer and Connector
on the Right Side

PA-47 - DC Power and RF Input Connector
on the Left Side

I connected the Propeller Project as the Exciter, a Low Pass Filter, the 50 Ohm Dummy Load, and the 12.6 Volt supply to the PA, the Fan came on (a good sign)!. The Propeller was outputting its 2.2 Volts into the PA input. . . . . But nothing was coming out of the PA, - more Dang!

I spent the next several hours trying to figure out the circuit or problem. Remember is a NEW untried circuit, and there is a chance it would NOT work at all. After spending more time trying to make it work. I decided, maybe "I Should Have" breadboarded the circuit first!

So, I started loading a fresh breadboard with components. With still more time (several hours) I still could not get anything to work as expected on either circuit.

The Bench

Dishearted - I gave up - left the shop "without" putting away my tools and cleaning up (I normally always clean up before leaving).

Bummer!!

Several days have past (about a week), it is now Sunday and I am planing to go to Jack's Homebrew Club evening meeting on Tuesday, and the following night I am going to the pQRP monthly meeting. I decided to clean-up the PA (to remove excess solder flux) to make it "look good", and take it to the two meetings, to show my epic FAILURE of a nice idea for the PA.

While cleaning the circuit board, I noticed one of the legs of the (necessarily) "dead bug" mounted transistors did NOT appear to be soldered (with filets) to its pad, it appeared to have just a glob (flyspeck) of solder on the bent leg. This was the drive transistor for the output power FET, maybe it was not actually soldered down!!

For me, it is actually quite difficult to see a single SOT-23 pad without a Microscope.

Under the Microscope I could see it only had flux between the pin and pad!! I heated the soldering iron, fixed the joint, re-connected the Propeller Beacon Exciter, the output Low Pass Filter, the 50 Ohm Dummy Load, and the 12.6 Volt supply, . . .

WOW!, I observed 43 Volts PP at the load. That is; (43/2*.707)^2/50 = 4.7WATTS - YES!!!!!

Which is a gain of 25.93dB.

The PA-47 Curcuit with a Sziklai Pair Driver works!!

I installed the rest of the TR circuit and Relay on the under side of the PCB, but - DANG! The relay would not work! Now what??

After several hours, I discovered that I had attached the Relay Coil to the opposite pins on the Library PCB pads within DipTrace, the Relay is polarity sensitive. Like the drive transistors I had jury-rig the Relay by cross wiring the coil under it to make it work (the fix can not be see in the photo).

After cross-wiring the coil pins and re-installing the Relay - All worked as expected :-)

PA-47 - With TR Circuit and Relay Installed

Regardless of Success or my Failures, Tess is always watching, to make sure everything is being done right! She was not involved with the PA design or PCB layout, but some how she must have missed the poor solder joint!! (actually, . . . she is watching her ball that I placed on the bench :-). If I had her concentration (and other admiral attributes), I may have NOT missed the above critical project details :-))))

Tess - Doing Her Job,
Production, Test, and Final Inspection

I am , . . . ah, . . we are NOW both Happy Campers!

. . . . . Tess has her Ball, and I have my PA!

I will later post more PA-47 Project details. More testing, and more work is needed to install angle brackets to support the PCB.

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UPDATE:

Increasing the DC supply of up to 14.2 Volts (via a heavy duty Lead Acid Battery on a Charger), I got 60 Volts PP at the 50 Ohm Load, (60/2*.707)^2/50 = 9.0 WATTS- Nice!!

Note to self:
A Fan control via the TR circuit or HeatSink Temp would be useful, it would save some power and would be quieter.

UPDATE:

Here is the PA-47 running on Jack's Bench at his Homebrew Club meeting, the photo was taken by Jack and who suggested this photo would make a great (complex) puzzle picture :-)

PA-47 Running on Jack's Bench

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