CQ with AIR

My Son and I are working on a project to automate; 20 air driven punches, with a similar strategy that was used by the old "pin printers", but our project will be on a much larger scale.

The planned punch printer will be much larger and much more powerful.

Air will be used to drive the punches and will be controlled via 12Volt air solenoids. I have previously posted the a description of the single test FET Driver that will be used, and which will be controlled via a microprocessor. The planned circuit for the finial product will consist of three stacked boards with 8 FET Drivers per board. The Toner Transfer of  the Prototype board is shown here.

Eight Circuit FET Driver Board

a Toner Transfer Prototype

To test the FET Driver, I needed a microprocessor to produce a test signal that would be easy to use.

From a previous project, I have an "Adafruit Trinket" microprocessor programmed to produce a "CQ" on one of it pins. A simple jumper was used to connect the Trinket to the FET Driver.

Trinket Sending CQ

The results was "CQ" being taped out by the air valve.

Air Valve Sending CQ

Once the air valve was connected to the cylinder,  . . . things got MUCH more interesting, and VIOLENT!

For this test, the air pressure was set at about 5 psi (34.5 kpa), for actual or normal operation the pressure will be about 40 psi (275 kpa). (I think I have the unit conversions correct)

Believe me, the following video does NOT fully capture the loudness or intensity of being - "ON THE AIR with AIR".

Pounding Out - CQ

Sorry for the rotated video (I will avoid that mistake with my future videos).

The test of the FET Driver? - It works great, . . . and I now know what it really means to "pound out" CQ.   :-)

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More 0402 Thermistors

In preparation of loading and testing the next revision of my PA47 Amp, I have started the process of joining FET and Thermistors, by mixing the glue - JB-Weld epoxy (see: previous posts).

For this build, I am using only JB-Weld, for the initial tack and then for the final cover. The JB-Weld web site provided some interesting data regarding strength and temperature resistant abilities. It suggests that JB-Weld is the right "glue" for this Thermistor attachment process.

It appears that a little too much of JB-Weld was mixed, but is actually is just a small drop, most of it will not be used.

Microscope at 7X

Here are some FETs with Thermistors attached with small mounts of JB-Weld. Soldered wires will be added after the epoxy has set.

2N7000 with Thermistors Attached

While under the Microscope I noticed that JB-Weld is not what it appear to the un-aided eye, it is actually gray with black flecks.

This the same as the First Image, only the
Microscope Set at 15X

After curing, this glob of epoxy was subjected to a test with a hot soldering tip, confirmed that JB-Weld is much more heat tolerant than Hobby Fast Cure Epoxy.

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Use of a 0402 Size Thermistor

This post and project is keeping with my On-Going Goal of working on very small projects as long as my eyes and steady hands allow.

The Thermistor Fan Control Circuit is working very well for my PA47 RF Power Amplifier (see selected links to previous posts). The PCB was re-laid out to include the circuit. Initially for testing, I just used an available 10K NTC Thermistor super-glued to the heatsink on a 1 Watt PA47 configuration.

For this project, my plan is to attach a small 10K NTC 0402 size thermistor directly to the 2N7000 for best FAN Control and cooling of the FET.

Here are some Microscope photos of the attachment process.

Shown is the 0402 Thermistor super-glued to the back of the TO-92 2N7000, along with the tip of a standard X-Acto Blade (for additional size reference).

Attached 0402 Thermistor on a TO-92 2N7000

A Wire Wrap Wire (30 AWG) was then soldered on each end of the Thermistor.

Thermistor with Wires Attached

A small drop of Epoxy was added to cover the connections and support the attached wires. Epoxy does not stick to the Kynar (wire insulation) very well (if at all). The wire connections may need better/more support.

Waiting for the Epoxy to Cure

I used Fast Cure Hobby Epoxy, but it will take over night to harden completely, in circuit testing maybe started tomorrow.

I am not sure of the thermal conductivity of Hobby Epoxy, perhaps something else would be better? Maybe another harder Epoxy such as JB-Weld?

This is ALL probably not necessary, but I wanted to see if I could do it. For future projects and use of Thermistors will probably be a larger size, and maybe not attached directly to the FET.

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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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