The 'Paraset' is a WWII Spy Radio and is the only Non-ESD Sensitive/RadHard QRP radio around.

The radio is also known as a Whaddon Mark 7 or Mark 7/B, one was placed in a leather brief case, one in a metal cash box and one in a wooden box. A later Mark 15 (also known as the Rival A3 or B2 minor) added an additional 6SK7 to the receiver to eliminate the regen radiation.

My Paraset is Black and sits in a small suitcase. You can see it by going to the ParasetBuilders Yahoogroup and going to the 'photos' section and look under 'w0rw'. I built it in 2004.

Thanks to Mario, IK0MOZ and Ken, W7EKB for posting all the technical information.

http://www.qsl.net/ik0moz/paraset_eng.htm and

http://www. mines.uidaho.edu/~glowbugs/paraset.htm

and Michael WA8YWO for the Yahoo Group.

To get on the ParasetBuilders Yahoogroup you have to send an email request

to michael at ParasetBuilders-owner@yahoogroups.com or

michaeltylerwv@yahoo.com

There is a Paraset article by Dave Ingram (K4TWJ) in the March 2005 issue of CQ Magazine, p.36.

My Black Paraset Pedestrian Mobile operation is featured on the front cover of

Low Power Communications, 3ed, by Richard Arland W3OSS/k7sz.

1. i started collecting parts for a year. i had a lot of trouble finding a good chassis, but it was sitting on my shelf all the time. It is 48 mil thick Aluminum clam shell design. It previously housed a "4th Network Satellite Stereo Processor", Model-3200, before i cannibalized it. It is 8.24 x 5.75 x 2.25 inches. There might be more of these in TV Satellite junk yards. i was going to build a silver/gray model but this chassis was already painted High Tech Black.

(The old MFJ-940 Versa Tuner II is just the right size for the Paraset chassis, but it has plastic or fiberboard sides...

The current MFJ-414 Morse Code Tutor looks like it is just the right size, 8.5"W x 2.25"H x 6"D and looks like it is solid metal. MFJ might be persuaded to sell a few spare chassis).

There was quite a bit of filing and mechanical fine tuning,

but i had the chassis holes all cut out in one day.

i started drilling holes and placing parts from the square TRW/Cinch (Jones) power connector, then on to the tube sockets because this chassis is about 0.25 inches shorter than the original.

The 3 pin power connectors were available from Ocean State Electronics in catalog (0204B, page 109), p/n's are PA-3 for the panel mount plug ($ 1.90) and SC-3 for the cable mount 3 pin female ($3.15).

It took about one day to cut the chassis and a day to wire the parts in place. i left the variable capacitor mounting to the very last to avoid damaging them

2. i still do not have a serial number plate for "B01" (Black No. 1). i think the real serial numbers were inflated, VE1NU has a real Paraset with the s/n of 10172.

3. Variable Capacitors: i used Oren Elliot Products, APC111G, 100pf, variables (oep@bright.net). They were fairly cheap but i had problems. i had to add a 1/4 inch to the main tuning capacitor shaft because it was too short for the knob. The old BC610 knob has its set screws way up near the top of the knob and would not grab the 0.4 inch long shaft. The Main shaft of the Qren APC111G is pressed on to the rotor shaft and the big BC610 knob, which wobbles as it goes around, finally pulled the shaft off the capacitor.

Because the shaft was too short, i had to drill the shaft out,

epoxy a screw inside and then epoxy a collar around it to get the shaft length out to 0.75 inches. It looks nice but will still put stress on the press fit shaft coupling. There needs to be some elastic relief on this shaft.

The variable capacitor used for the main tuning should have a straight through or welded shaft that is 0.75 inches long for this knob to be used.

4. The 'Tank" variable capacitor must have an insulated mounting system or else the shaft will short the B+ to chassis ground. The Oren APC111G does not have an insulated rotor. i used fiber insulating shoulder washers to insulate it. i used a rubber washer under the Tank knob to prevent contact with the HV on the front panel.

REMEMBER this radio contains LETHAL voltages !

This is not a transistor radio.

You can modify the Tank circuit by connecting the Tank variable capacitor rotor to ground, (That will but B+ across the Tank variable capacitor but that is better than having B+ on the rotor shaft), by adding a series 0.01MFD cap you can keep the B+ off the Tank variable capacitor completely and still have a grounded rotor shaft.

5. Most of the terminals and sockets and tubes came from OEM, the local Colorado Springs surplus parts store...but Ocean State Electronics has most of these small parts too.

OEM has metal tubes, (i use 12V tubes on 12V but i use a glass 12L6 or 12V6. The original "P" was powered from a 6V battery). OEM is at 2727 Palmer Park Blvd., Colorado Springs, CO 80909. They don't have a good mail order operation. Phone 719-6350711. The BC610 knob came from Surplus Sales of Nebraska, www.surplussales.com.

6. i still need 3 fluted knobs for the Tank/Ant/Regen, however the ones i have now look pretty good.

7. i have 2 round Bliley BC3/HF2 crystals for 7038.5, and 3680.

The crystal socket is a "National" 2 pin socket.

Do not use small crystals in the transmitter because they will drift and possibly crack. The crystal current is high.

This transmitter needs FT243 style or bigger crystals.

8. i converted the T/R switch from a 4 position rotary to a 2 position by opening it up and changing the stops.

9. i used black countersink hardware since the chassis was so thick.

10. The Receiver coil wire is 35 turns (spires) #22 AWG, and 4 turns #22. My receiver coil is wound on a 1 inch diameter plastic pill bottle.

The transmitter coil was wound on a 1.5 inch Bakelite coil form. The Tank is 18 turns of #14 or #15, The Aerial is 22 turns #20. You can decipher this from the parts list...

http://www.qsl.net/ik0moz/lj_parts.jpg

The original "P" used screw base 6V tuning lamps. i used a small self leaded 6V bulb in a grommet. The link was one turn for each lamp.

11. i made the key from an old telephone relay contact stack.

It works really well for a nonadjustable key. i can send 25 wpm on it.

12. i used an old plate to speaker output transformer for the 36H audio choke (460 DC Ohms). It gives plenty of audio for my 2000 ohm

C.F. Cannon Co., No.15, Alnico Magnetic headphones.

See http://www.decodesystems.com/help-wanted/chief-headphones.html for a description of these old headphones.

13. Don't use the tube socket pin 1 for a tie point.

(If you plug in metal tubes, you might inadvertently put 350V on the outside of the tubes).

Ground all pin 1's and use metal tubes for more regen and Tx stability.

14. A 2 turn loop around the Tank coil is a good 50 ohm pick off point for a coax fed resonant antenna.

15. An external key jack in the back would be nice for an external bug...

16. My 'gimmick' turned out to be about 2 inches long, not very critical.

17. i made a small AC power supply for +350VDC.

It has a small Triad R-29A, 6VAC/350VAC transformer, 8 H Choke, full wave silicon rectifier and 2 - 20 MFD capacitors. This gives me very low AC ripple output.

18. i made a 12V DC vibrator power supply for my Paraset from an old Motorola TU117. This supply is giving me 360VDC and is drawing 2.5A on receive and 3.4A on transmit. The Battery life (BB590) is a little over 1 hour.

This supply can also operate from 6V by changing the jumpering.

The supply came out of a 9" Motorola "Twin V" T41/T43 trunk mount radio. The vibrator power supply, the BB590, and the AC power supply fit in a regular briefcase and weigh 21 pounds. There is a picture of the power supply briefcase on the ParasetBuilders Yahoogroup "Photos" section.

This briefcase goes into my backpack for Paraset Pedestrian Mobile operation.

When i use a 12V power supply, i use 12V tubes (12SK7's and a 12V6).(i am still working on a Replica vibrator power supply. i hope to make it fit into the same carrying box as the Paraset).

19. i used the schematic version that is on the ParasetBuilders Yahoogroup...

The 1.5K receiver supply resistor is doing fine at 2W. i also used a 10K 2 Watt feeding the receiver from there.

The Tx cathode resistor is 220 ohms, 1W.

There are mistakes on some schematics,

Like pin 3 of the regen tube s/b going to pin 5, the tap on the coil.

The audio out coupling cap s/b 0.1 MF. Make sure this is a good 600V capacitor, it is the only thing between your ears and +300V. A single point failure mode at this part would not be good.

20. You can double the power output of the Paraset by using a 6L6 in the transmitter.

21. i put my Paraset in a small clamshell suitcase that is 5 inches deep, so i don't have to unplug the tubes to close the case. There is a picture of the 'Black Ops Paraset' and the case in the ParasetBuilders Yahoogroup ‘Photos’ section. It weighs 5 pounds.

i planned to use a replica decorator Leather Briefcase for the Paraset case but the "Z" axis got out of control. My Paraset is now 3.5 inches high when the tubes are pulled.

22. Paraset Frequency Spotting...

Here is a way to spot your transmit frequency on your Paraset..

Just add a 0.5 Megohm resistor (1/2W) from Input B+ to the transmitter B+ line.

(This can be done right across the T/R switch).

This keeps a small amount of B+ on the transmitter while you are in receive and when you push the key down the oscillator should take off.

You will have to back off the regen a little (varying the regen control changes the frequency so you have to keep it constant) and you might have to trim the tank capacitor, but this will turn the oscillator on and allow you to spot your transmit frequency on the receiver.

The 'spot' may just sound like a chirp but you will be able to spot the frequency.

The resistance value will vary with your B+ value and the activity of your oscillator circuit.

You can also put your crystal in series with your antenna and tune around until you hear a pop.

23.Sidetone..

The internal Paraset regen receiver really gets blocked out and can't be used for sidetone.

i use an old pocket transistor AM broadcast receiver for monitoring my transmitted signal. Just place it near your antenna and tune around for a nice signal.

24. Bandspread: Unauthorized Modification #1

The regen receiver is very unstable and there is no bandspread on this original version. My Bandspread modification schematic and wiring pictures are in the "w0rw Paraset" Photos on the Yahoogroup.

i used a 3 position switch to add in trimmers and give 40 & 80 meter bandspread plus the original Paraset broad tuning range.

(i used a 1/2 inch diameter Grayhill 7908 rotary switch,

The 7908 is a momentary rotary switch and i had to modify the detents inside, Any small 2 pole, 3 position rotary switch will work). i put this switch just above the T/R switch.

The bandspread is achieved by setting the upper edge of the band with a trimmer and then adding a low value trimmer in series with the main tuning variable capacitor to set the span.

This gives me 180 degrees of rotation for 200 KHz.

The switching could be done with PIN diodes and the tuning with varicaps, but where does 'Replica' end ?

There is a Paraset bandspread modification in Electric Radio Issue #179, April 2004, by KE3OQ. See http://www.ermag.com for back issues. i don't have a copy of his modification.

This method gives good mechanical bandspread.

25. Receiver Calibration.

You can get the calibration charts off of ik0moz's web site at http://www.qsl.net/ik0moz/Tabella.jpg (Tabella means Table) and you can plot the new tuning dial correlation numbers on this reference chart. The calibration should be done right at your

normal regen threshold because backing off the regen control can result in up to a +50 KHz dial deviation. Antenna capacitance, (Long coax), can cause receiver calibration shift too. The regen control becomes a nice fine tuning frequency control. There will now be 3 calibration charts if you have installed the bandspread modification.

The Ordinate for the Bandspread Charts will be 7.00 to 7.20 MHz and 3.50 to 3.60 Mhz.

26. Overloading.

The receiver is easily overloaded by strong stations, and is very susceptible to overloading by strong international broadcast stations when it is on a good antenna.

The simple solution is to use a short 1/4 wave vertical.

I use a little 1K pot in series with the receiver input coil which acts as an RF Gain control...Did i forget this is a 'replica' again ?

EpiBlog:

It was a lot of fun to build. When was the last time you sawed off a one quarter inch potentiometer shaft and

what are you going to do with all those old parts in your junk box ?

It is amazing that all those old parts still work.

i have carbon comp. resistors in it that are over 40 years old.

i did not use any old electrolytic capacitors.

It fired up right away the first time i applied power to it..

All those 'spire' winding instructions were correct even thought

they were written in French, (e.g.: Aerial: 22 spires 20/10 isolant coton compris interieur du mandrin, de chaque cotes spire de couplage).

i contacted 65 stations with my Paraset on a Sprint contest on 40 meters on 2/7/05. These days you have to call CQ or 'spider'

(monitor) your crystal frequency and wait for someone to come along and call CQ on it. i called a station in Finland, who happened to be on 7048.5 the other day, with no success.

In the old novice days, the novice bands were worked cross band, because all the novices were crystal controlled and could not zero beat each other.

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In case you don't know what a Paraset is...

The PARASET is a small British "Spy" transmitter/receiver supplied to the resistance forces during WWII mainly in France, Belgium and the Netherlands.

It uses 3 metal tubes :

1) 6SK7 - Regen. Detector

2) 6SK7 - AF Amplifier

3) 6V6 - Crystal Oscillator/Power Amplifier

The range covered by the receiver is 3.2 - 8 MHz on AM and CW modes.

The transmitter is crystal controlled and works on the same frequency range.

The power output is around 5-7 W on CW mode only.

The set was originally supplied by a small 6 VDC vibrator power supply.

Paul w0rw

w0rw1@msn.com