Dan's amateur Radio Page:

I obtained my Technician Class license back in 1971 when the Tech exam was done by mail. Several weeks later I was granted the call WA6OIL. This happened at the same time as the Santa Barbara oil spill and my "friends" never let me forget it! :-) My first interests were in the microwave region and six-meter ops. Six I particularly enjoyed. I have a six-meter WAS (#496) and am SMIRK #1356. I upgraded to Advanced in 1978. Moving to the Pacific Northwest in late '82 I retained my call as it was considered an "Old Timer's" call by then and I thought it was a pretty slick call. Slick - get it? Heh-heh...heh.....heh - OK, I'll quit now.

My interests have changed through the years and I now consider forty meters to be in the UHF region. I enjoy ops on 160-meter phone and CW. I am a big adherent of the establishment of "sub-broadcast band" Amateur allocations in the 500 KHz and the 136 KHz segments, perhaps 160 to 190 KHz as well.

In 2004 I was bit by the vanity bug and changed my call to something more fitting to the area. A distant cousin who passed away in 1980 held the call W7OIL so I applied for it. So now I have a "really old-timer" call to go with my main interest of building vacuum tube receivers and transmitters. Please scroll down to see some of my projects. 

On Saturday, 17 September, 2011 I went down to the VE exam session at the American Legion. I wanted to have them "grandfather" my wife Patti - N7FAF, to General Class from Technician Class. While there I took a shot at the Extra Class - and passed! So now I am at the top of the heap and Patti has her General. Ain't no way I'll change the call!

The Paraset:

(An Original Paraset)

Several years ago I subscribed to the Yahoo! "ParasetBuilders" group. Another fine forum based in France is the "Les Amis du Paraset" group. The Paraset was a small transmitter/receiver used by the "Resistance" groups in most notably Norway and the Netherlands during WWII. It was a small affair, barely 8" x 5" x 3" with a three tube complement, two 6SK7's as a regenerative detector and audio amplifier and a 6V6 for transmit. It had a tuning network that would enable to work into just about any type of antenna.

These groups have kept the memory of the Paraset alive by building and operating replica Parasets whose level of accuracy extends from VERY accurate to "OK so it ain't perfect but the parts are bloody well hard to get". The spirit of the Paraset is there as is the challenge of operating one.

My first completion (I sold the first unfinished) was of a hypothetical Paraset Mk-IX "built" for the US Army Signal Corps for use in the Pacific theater of Operations. It sounds plausible anyway. The electronics are the same as the original.

(My "Mk-IX" Paraset)

My "Mk-IX" nameplate and Yours Truly reporting Nazi troop movements in NW Washington State.:-)

 

Paraset-2010:

I guess the "third time's the charm:. This one is a more "authentic" Paraset as it has nearly the same dimensions and even has "ORIGINAL" Paraset knobs. These knobs were manufactured in England by the same manufacturer who had the original forms for the original Parasets. The only mod I plan is to make it for operations on 40 meters. The original receiver tuned from 3 to 8 MHz which makes the two ham bands only a few divisions wide each. This bugger is touchy enough to tune so spreading the desired ham-band over the entire dial is a must.

Paraset-2010 tunes from 6.95 to 7.21 MHz with the tuning capacitor network I designed. The receive tuning coil is "per original". Paraset-2010 is designed for 12-volt operation for convenient portable operations. The receiver uses two 12SK7's, one as a detector and the other as an AF amp. The transmitter is a 6V6 oscillator putting out about 5-watts into a 50-ohm load. The 6V6 needs a ballast on the filament for 12-volt ops. A 15-ohm, 10-Watt resistor will do the trick. So will three #47 or two #40 pilot lamps wired in parallel. With the parallel tank and series antenna circuit it will load into just about any antenna. The best DX so far (as of mid-February, 2010) is Michigan from SW Washington State on a 200' long wire antenna. No antenna tuner - I was able to cram about 100mA of antenna current into the wire. A tip of the hat to the designer of this rig. 

As you can see the front panel is a simple layout. The original used a "General Radio" type tuning knob with a friction drive vernier knob for fine (?) tuning. Since these are as rare as rooster lips I have eschewed the friction drive for a very small value (around 8pF) variable capacitor for fine tuning. Thus the appearance of the rig is not changed while retaining a good fine-tuning control. The "innards" are pretty busy but since layout of the wiring is not very critical you can finagle parts around a bit. Below are photos of the fine-tuning arrangement and the link coils for the indicator lamps. The crystals used are of the FT-243 type rather than the original cylindrical type. The small jack below the crystal socket is for an external key. The "recipe-box" was built by me expressly for this set. 

Something that was pointed out to me by Steve McDonald - VE7SL, is the use of 6v, 150mA (#47) bulbs for tuning indicators. Since 6v times 150mA equals 900 milliwatts that means at full brilliance the bulbs are eating 1.8 WATTS of your output. Ewwww!!! He suggested #49 bulbs which are 2v, 60mA units. Both at full brilliance suck out 240 milliwatts, a much more digestible value. Watch out though as these bulbs can burn out much more easily. You can see in the photo of the link detail that the link is bent outwards from the coil to tone down the RF coupling.

The "recipe-box" was built by me expressly for this set. It is made from 1/4-inch (6mm) red oak. Careful observation of the lid will show that the color doesn't match the rest of the box. I made the lid a year after the box so it has not "aged" to the same patina. It is always better to make the lid the same time as the box as back-fitting a lid is a pain! The clips for the tubes and the indicator lamps are formed from galvanized roof-flashing.

And now the schematic: Right-click on schematic to save at full resolution.

The names of the controls are in "English-English". Hence the "A" and "E" at the antenna connections stand for "Aerial" and "Earth". "Reaction" means "Regeneration" and the rest are real words. ;-)

Another mod by Steve McD. is to put a 45-volt Zener diode across the "Reaction" potentiometer. You can use four 12-volt units in series to accomplish the same result, which is to make the reaction control much more stable in operation.

The "Tank" and "Aerial" transmit controls are a "tune for maximum brightness" operation. I've gotten good reports with this set. There is a tendency for it to be "chirpy" but careful tuning will minimize this. Listening to the transmitted signal with a separate receiver is a big help.

A DC/DC Power supply for the Paraset:

The Paraset does not operate very well without power. The original had a supply for "Mains" operation (220vac European house current) and another one that used a 6-volt storage (car) battery. Since I wanted to have the capability of operating "in the field" I wanted a supply that runs on 12-volts DC. I found a circuit on the internet that would fit the bill so I made some modifications to it to give me 12-volts DC for the filaments and 400-volts B-plus. The circuit consists of a multivibrator oscillator using two NPN power transistors. Several power resistors are used for oscillator timing and ballasting. This drives a filament transformer secondary winding (Yes, the transformer is wired "backwards"). The primary winding is connected to a voltage-doubler circuit that creates the 400-volts DC for the tube plate circuits. Here are some photos and the schematic.

     

     

     

The 6"x 5"x 4" box is a reasonable size for a replica power supply. The ventilation holes are necessary to help dissipate the heat generated by the resistors and transformer. The transistors do not need that big heatsink but they were a pair already mounted so I did not try to remount them. A heatsink half that size would suffice.

The GH-1 Regenerative Receiver:

For the longest time I wanted to make a top-level regenerative receiver. While I was volunteering at the "American Museum of Radio and Electricity" in Bellingham, WA (Which I HIGHLY recommend visiting) I had a chance to examine and work with the National SW-3. The SW-3 was a Depression-era Ham and general-coverage 3-tube receiver. It has a novel plug-in coil design that allows both general coverage of the BCB and SW broadcast bands and "bandspread" Amateur band tuning. My friend Mike Peebles has always talked about a "Holy Grail" set so I thought calling mine by the spoonerism "Groly Hail" set would not violate any copyright claims. :-) Hence the "GH-1"

The National SW-3 Regenerative Receiver:

And now for my version...

Note the operative term here is "version". I did not try to make an exact copy as there were several things I did NOT like about the SW-3. I wanted to use octal battery tubes instead of the original SW-3 power supply that frankly looked kind of sinister. I did use the general coverage/bandspread plug-in coils idea and a vintage National "Velvet Vernier" tuning dial. I found the "pancake" regeneration control under the tuning knob to be handy as you have to ride the regen while using the SW-3. Ditto the GH-1. The control to the left of the tuning dial is the RF gain and the right-hand knob is the AF gain.

The Schematic: