Solid state vibrator for the BC-1000 PP-114/VRC3 A & B

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YLG80
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Solid state vibrator for the BC-1000 PP-114/VRC3 A & B

Post by YLG80 » Mon Nov 20, 2017 9:25 am

I've got a rather cheap BC-1000 (French model) coupled to a PP-114 model A (US) in good shape.
Of course the vibrator was not functioning.
The previous owner had already uncrimped the vibrator can and bent the contacts so that the vibrator mechanical
part was dead for ever.
PP-114_146B_VIBRATOR_MECHANICAL_UNIT.JPG
PP-114_146B_VIBRATOR_MECHANICAL_UNIT.JPG (156.02 KiB) Viewed 943 times
Not a problem as my intent was to convert the vibrator to a modern solid state circuit to be placed inside the original can.
Purists, don't worry: once complete the mod is invisible and you can still hear the loud buzzing sound :D :) !

As it was a design proofing, I've made the solid state vibrator on a prototyping board but there is PCB layout available that can be made.
After many test with sometime some smoke, the final circuit is OK. However, and that was the cause of the smoke, one wire has to be moved
from one pin to another in the PP-114A/B. This was a strange design and it took me some time to find the problem.

Here is the schematic based on an original design found on the http://myvintagetv.com/ss_vibrator.htm forum.
6V_SS_VIBRATOR-146B_PP114A-B.jpg
6V_SS_VIBRATOR-146B_PP114A-B.jpg (158.81 KiB) Viewed 1051 times
Here is the prototype circuit using SMD MOSFETS replacing the mechanical vibrator on the same socket.
SS_VIBRATOR_146B_PP114_BOARD_ASSEMBLY_HOUSING.JPG
SS_VIBRATOR_146B_PP114_BOARD_ASSEMBLY_HOUSING.JPG (143.82 KiB) Viewed 1051 times
More details to come.
Last edited by YLG80 on Sun Nov 26, 2017 11:13 pm, edited 4 times in total.
Ford GPW 1943 - Louisville - DoD 12-7-43
serial 164794


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Re: Solid state vibrator for the BC-1000 PP-114/VRC3 A & B

Post by YLG80 » Mon Nov 20, 2017 9:38 am

Here is a PCB drawing that will be OK with the schematic posted above.
SS Vibrator pcb1.1.png
SS Vibrator pcb1.1.png (57.6 KiB) Viewed 1046 times
When printing, don't forget to rescale the layout by measuring the CD40476B pin pitch (2.54mm)

Here is the assembly drawing (PBA components side) with the correct components for a 180 Hz vibrator.
SS_VIBRATOR_146B_PCB_TOP_VIEW.jpg
SS_VIBRATOR_146B_PCB_TOP_VIEW.jpg (69.65 KiB) Viewed 1046 times

Ground jumpers for the standard power MOSFET transistors.
SS_VIBRATOR_146B_SOURCE_GROUNDING.jpg
SS_VIBRATOR_146B_SOURCE_GROUNDING.jpg (48.04 KiB) Viewed 1046 times

The CD4047 IC is a CMOS multivibrator that will remain powered to max 6.2V.
The frequency has been adapted to about 180 Hz by means of the 24K resistor and 0.047µF.
Fosc calculation is 4.4 X R X C and Fq (driving the MOSFET)is Fosc divided by 2.
With the value used Fq is very close to 180 Hz, which is not critical providing that the PP114 transformer magnetic circuit is saturated.

./..
Last edited by YLG80 on Mon Nov 20, 2017 9:16 pm, edited 1 time in total.
Ford GPW 1943 - Louisville - DoD 12-7-43
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Re: Solid state vibrator for the BC-1000 PP-114/VRC3 A & B

Post by YLG80 » Mon Nov 20, 2017 12:47 pm

Here are two close-up views of the prototype circuit with the SMD MOSFETS.

Copper side with the two switching MOSFETS.
Details on the 1.5mm² grounding wires to support the 7 Amps drawn by the PP-114 in 6V.
SS_VIBRATOR_146B_PP114_BOARD_WIRING.JPG
SS_VIBRATOR_146B_PP114_BOARD_WIRING.JPG (174.9 KiB) Viewed 1037 times
The connections between the circuit and the socket are shown on the schematic posted here above.

Two wires are soldered to each MOSFET drain pin also to support the 7 Amps peak.
The MOSFET are remaining totally cold when using the BC-1000.


Components side with the multivibrator CD4047 without and with the 2200µF capacitor between Vcc and GND.
The three 6.2V zener diodes.
SS_VIBRATOR_PP-114_TOP-VIEW.JPG
SS_VIBRATOR_PP-114_TOP-VIEW.JPG (126.94 KiB) Viewed 1037 times
SS_VIBRATOR_146B_PP114_BOARD_TOP_VIEW.JPG
SS_VIBRATOR_146B_PP114_BOARD_TOP_VIEW.JPG (148.72 KiB) Viewed 1037 times
There is no issue to use conventional (i.e through hole) components as there is enough space inside the vibrator can.

Curiously for a military equipment, there is no real notch in the vibrator socket to avoid inserting it in the wrong position.
It seems that the vibrator had once been forced into the wrong position in my PP-114.

Here is a picture showing the correct positioning of the two large dia. pins.
SS°VIBRATOR_146B_PP114B_VIBRATOR_PS.JPG
SS°VIBRATOR_146B_PP114B_VIBRATOR_PS.JPG (163.88 KiB) Viewed 1037 times
Next I will show the PP-114 little mod to make the vibrator working correctly.
If you assemble the vibrator directly without the mod, you will hear the buzzing sound, but the BC-1000 will not work and one of the two MOSFET
will start burning, while drawing the max 7 Amps current from the battery.
The MOSFET connected to pins 1-2 of the vibrator socket is overheating :oops: :oops: .
Despite of the problem, voltages measured everywhere in the PP-114 are within spec. but the two CK1005 diode tubes are not rectifying the HT.

./..
Last edited by YLG80 on Fri Nov 24, 2017 6:54 am, edited 4 times in total.
Ford GPW 1943 - Louisville - DoD 12-7-43
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Re: Solid state vibrator for the BC-1000 PP-114/VRC3 A & B

Post by YLG80 » Mon Nov 20, 2017 10:26 pm

Unlike other solid state vibrators, this design make use of a standalone multivibrator (CD4047) that needs to be correctly powered with a stable 6 volts power supply in order to produce a high frequency signal to drive the FETs.
The 180Hz high frequency is important in the PP-114 in order to keep the power supply regulation system working.
The regulation system is based on magnetic saturation.
I've scoped the vibrator switching frequency when installed in the power supply and the frequency was way below the expected 180hz.
The reason can be found analyzing the schematic.
Here is a copy of the schematic found in the PP-114 cover.
The different voltages are shown In that schematic which is convenient to debug any problem.
I've colored in RED the positive voltage and in BLUE the ground lines.
BC-1000_PP-114B-and-C_SS_Vibrator_mod2.jpg
BC-1000_PP-114B-and-C_SS_Vibrator_mod2.jpg (227.82 KiB) Viewed 1016 times
On the left side of the wiring diagram, there is the vibrator coil connection marked 6V in red.
The red dotted line shows that the vibrator is powered by a switched signal coming from the transformer primary circuit through the voltage selector switch connection B.
Despite of the 2200µF capacitor in the SS vibrator circuit, that switched power cannot be used by the circuit.
We need a steady and clean power supply.
Fortunately that power supply can be found nearby on the B pin of the 6-12-24V voltage selector switch, just above A in the schematic.
So we need to disconnect the wire connected to B and move it A.
This is rather easy to make as shown on the next picture.
PP-114B-C_WIRING_MOD_SS_VIBRATOR.JPG
PP-114B-C_WIRING_MOD_SS_VIBRATOR.JPG (168.47 KiB) Viewed 1016 times
The two red dots are showing where pin 3 of the vibrator is connected.
The picture shows the original position of the wire (B) to be moved and soldered to position A.
In that position the vibrator will be powered with a stable power coming from the main ON/OFF relay.
If the PP-114 is switched to 12V or 24V, the SS vibrator internal regulation to 6.2V will keep the CD4047 vibrator power voltage down to 6V.

Once modified, the PP-114 works beautifully producing a loud buzzing sound.
The vibrator circuit, and particularly the MOSFET transistors, is remaining cold.
At that stage you need to verify the PP-114 output voltages and check if they are within spec. In my device, all voltages are correct.
Don't forget that a solid state vibrator has a far better yield than the mechanical one so that higher voltages could appear at the output.
If it's the case you would need to add 2 power diodes in series with the vibrator switching output pins, 1-2 and 5-6, as explained in the vibrator schematic.
This would lower the primary transformer voltage.

Final and important note : this solid state vibrator works with the PP-114 models A and B.
The vibrator is wired differently in the original PP-114 and I cannot test how to adapt that design to this first model.
I've a model B only.
Rewiring the vibrator like in model A and B would likely be the solution.

Now you may insert the solid state vibrator into the original can and crimp it back.
Don't forget to double check the PP-114 capacitors and change them if necessary (leakage).
New capacitors could likely be installed inside the original caps casing in order to preserve the original aspect.
Yves
Last edited by YLG80 on Fri Apr 20, 2018 9:21 am, edited 5 times in total.
Ford GPW 1943 - Louisville - DoD 12-7-43
serial 164794

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YLG80
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Re: Solid state vibrator for the BC-1000 PP-114/VRC3 A & B

Post by YLG80 » Mon Nov 20, 2017 11:20 pm

Other tips:

In order to remove the mechanical vibrator from the socket, heat up the pins using a fine tip soldering iron.
Push the soldering iron tip on top of the pin where the wire is soldered.
You will remove the wire by pulling it from the other side.
Once all wires are removed, heat up again each pin from the top.
Once the solder melts, quickly remove the soldering iron tip an blow air through the pin. This will leave the pin empty and clean.

You can use any power MOSFET N-channel providing that Vdss is higher than 30V-50V and RdsON is lower than 0.10 ohms, not critical.
Transistors can be found in the IRFx range from International Rectifier.
For example the IRFZ74 (Vdss 60V - Rdson .05 ohms - Ids 30A) would do the job. Or two BUZ11 with about the same specs

Prior to reassemble the power supply into the casing, check if the main transformer screws are correctly tightened.(reduce vibrations)
Ford GPW 1943 - Louisville - DoD 12-7-43
serial 164794


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