Michael J. Rainey: July 2011

Description: Several months ago, a surprise package arrived in the mailbox. An anonymous donor had sent three old Germanium transistors: the 2N170 and a pair of 2N107s (all date-coded December 1956), still in their original plastic tube packaging. A thin booklet titled "Type 2N107 Transistor Circuits for Experimenters and Amateurs" was also included. The circuits shown in the booklet appear to be aimed at beginners, featuring audio amplifiers, code practice oscillators, and similar projects. However, the "Simple Radio Receiver" caught attention, reminiscent of early interests in homemade AM radio receivers while growing up in St. Louis, Missouri, during the late 1960s. Although current AM radio broadcasts are less appealing, there is nostalgia for the simple circuits that marked the initial steps into amateur radio. This same circuit also appeared in the first through seventh editions of the General Electric Transistor Manual, from 1957 to 1964. Although there is no current interest in listening to broadcast AM radio, a direct-conversion receiver for copying CW only requires the addition of a beat-frequency oscillator (BFO) to the receiver circuit. With sufficient BFO drive, the Germanium diode can function as a commutating mixer. However, a single diode mixer has notable disadvantages, including a lack of AM signal rejection, increased spurious frequency energy, and inferior port-to-port isolation compared to more advanced designs. Despite this, curiosity about how well such a basic radio would have performed in the late 1950s persisted.

The circuitry on the left side of the proto-board features a crystal-controlled (14.059 kHz) beat-frequency oscillator made from a Philco surface barrier transistor (1959 date code). This oscillator generates 13 mW of RF output power. A miniature 50-ohm potentiometer serves as the oscillator load and BFO input signal power splitter. A cat's whisker and galena detector functions as the switching mixer in the setup. Alternate mixer diodes are present, including a classic large glass 1N34A made by Sylvania in the early to mid-1950s and a red plastic-packaged 1N66 (date-coded March 1957) diode made by Raytheon. Signals were received immediately upon powering the new receiver, with the Sylvania 1N34A initially used as the mixer diode. When the QRP calling frequency became quiet, an RF bench signal generator was substituted for the crystal-controlled BFO to explore the band. After logging several DX calls, the Raytheon 1N66 was tested, followed by the cat's whisker and galena, which appeared to be at least as sensitive as the vintage commercial diodes in this application. A notable contact was made with F6HFX operating 5W from the southwest of France, with a station in Florida struggling to maintain communication. Other stations heard included OZ0TX, PA3CJP, 4O8A, OK2AN, YT2ISM, OK4RQ, G3VMW, DM4IM, DL0KWH, LY5A, CR7ACS, and DF8GI.

The impedance looking into the base of the 2N107 AF amplifier is 2740 ohms, with Ic = 388 µA, Ib = 10.7 µA, Vc = 1.49 Vdc, voltage gain = 44.3 dB, and power gain = 36.1 dB. Images from the 1957 Radio Shack Catalog feature listings for the Sylvania 1N34A, Raytheon 1N66 diodes, and the General Electric 2N107 transistor. The 2N107 was priced at $0.99 in 1957, equivalent to $7.95 today when adjusted for inflation. Even "low-end" electronic components were relatively expensive at that time. The 2N43, 43A, 44, 45, and 2N107 transistors were graded products from the same fabrication line. Initially discarded as rejects, the 2N107 was later recognized for its value to electronic hobbyists. This transistor line was introduced in September 1953, marking the first alloy junction devices produced. John Saby was the lead developer, while the alloy junction process was invented at GE in 1950 for rectifiers. Due to the unprotected semiconductor surfaces, GE evacuated their early transistor envelopes to nearly vacuum tube levels, explaining the metal "pinch" found at the top of these early "tophat" transistors. The datasheet power gain listed for the 2N107 is 38 dB, and it is noted that the 2N107 still produces 36 dB after 54 years of use.

A Sputnik QSO Party transmitter prototype produced an RF output power of 450 mW with 70 Vdc at 14.4 mA on the V2 anode. The V2 screen (G2) current is 1.6 mA, and the V1 anode current is 1.05 mA with 45 Vdc at 176 µA at the screen (G2). These vacuum tubes are capable performers, but it is essential to adhere to maximum electroderatings as specified in the datasheets. The simple MOPA (Master-Oscillator -> Power-Amplifier) vacuum-tube radio transmitter circuit was well-known in the mid-1950s. A crystal-controlled Pierce oscillator drives a Class-C PA, with the PA grid bias derived from rectified PA grid current. The CW keying and transmit/receive switching circuitry are not depicted in the circuit. The original Sputnik-1 keying plan involved alternating the 40.002 MHz transmitter and the 20.005 MHz transmitter to maintain a steady battery load. A low-pass filter may be required between the Pi-network impedance matching circuit and the antenna, with adjustments to the capacitor value (C1) necessary for optimal oscillator feedback and proper loading capacitance for the quartz crystal resonator.

The RF output power was initially 75 mW, dropping to just over 50 mW by the end of a month-long trip. Despite not making contacts with the Americas from Europe, several successful QRP/QRPp QSOs occurred along the way, demonstrating the effectiveness of the simple circuits and equipment used.Some months ago a surprise package turned up in my mailbox. Ananonymous donor had sent me threewonderful, old germanium transistors. The2N170 and a pair of 2N107`s (all date-coded December 1956) werestill in theiroriginal plastic tube packaging. Athin booklet, Type 2N107 Transistor Circuits for Experimenters [and] Amateurs, was also included. Thecir cuits shown in the booklet appear to be aimed at the rank beginner:audio amplifiers, code practice oscillators and the like. However, the "SimpleRadioReceiver" caughtmy eye (lower right-hand corner below). This was exactly the sort of project that captivated me in my early youth. Growing up inSt. Louis, Missouri in the late 1960`s, Ienjoyed listening to baseball and ice hockey games on KMOX, and pop music on KXOK, using a wide variety ofsimplehomemade AM radio receivers.

Although there`s nothing much ofinterest to me on the broadcast AM radio dial these days, Ihave a nostaligia forthe simple circuits thatmarked my first stepsin amateur radio. By the way, this same circuit also appeared in the first (1957) through the seventh (1964) editions of the General Electric Transistor Manual.

While I`m not now interested in listening to broadcast AM radio, a direct-conversion receiver suitable for copying CW only requires the addition of a beat-frequency oscillator (BFO) to the above receiver circuit. With sufficient BFO drivethegermanium diodecan be made to function as acommutating (switching) mixer.

On the other hand, a single diodemixerhas several notable disadvantages; perhaps the worstis therelative lack ofAM signal rejection. This type of mixer alsocreates more spuriousfrequency energy and the port-to-port isolation isquite inferior as compared to more advanced designs.

Nevertheless, the more I thought about it the keener I became to find out how wella lad might have donewith such abasic radio in the late 1950`s. on 20m perhaps Fortunately, all it took was a pleasant evening to find out. The circuitry on the left-hand side of the proto-board in the above photo carries a crystal-controlled (14.

059kHz)beat-frequency oscillator made from aPhilcosurface barrier transistor (1959 date-code). Thisoscillator generates 13mw of RF output power. A miniature 50 Ohm potentiometer acts asthe oscillator load and BFO input signal power splitter. Yes, that`s a cat`s whisker and galena detectorworking as the switching mixer in the above photograph! Alternate mixer diodes are shown in the foreground. The left-hand diode is a classic, large glass1N34A made by Sylvania in the early to mid-1950`s. To the right is a red plastic-packaged 1N66 (date-coded March 1957)diode made by Raytheon. Thiswas Raytheon`s equivalent to Sylvania`s hot selling 1N34A. Signals were heard as soon asIpowered-upmy new receiver. I began using the Sylvania 1N34Aas my mixer diode. When things became quiet on the QRP calling frequency I substituted my RF bench signal generator for the crystal-controlled BFO, in order to roam around the band.

After logging a dozen or so DX calls I switched first to the Raytheon 1N66, and finally to the cat`s whisker and galena. The galena appeared to beat least as sensitive as my vintage commercial diodes in this application. The catch of the night came with thecat`s whisker and galena installed whenI copied F6HFX running 5w fromthe southwest of France!Astation in Florida that Pierre was working hada fairly rough copy, judging from the number of repeats requested.

TheFloridian lost him several times before throwingin the towel. Pierre`s signal was also comingand going here, but with spells ofdecentcopy in between. Another station heard with thegalenawasG3HGE. Tom had a huge signalhere for well over an hour. It was a real pleasure to copy himsending withhisoldbug. Some of you may recall his company, TW Radio; a history of which may be found by clicking here. A few of the DX stations heardinclude:OZ0TX, PA3CJP, 4O8A(big sig), OK2AN, YT2ISM, OK4RQ, G3VMW, DM4IM, DL0KWH, LY5A, CR7ACS, and DF8GI (579on the galena). Altogether, I filled two sheets of notebook paperwiththe callsigns heard that evening. I hearda number of weaker domestic stations calling CQ(with no answer) near the QRP calling frequency; presumably someof which were running 5w or less.

The impedance looking into the base of the 2N107 AF amplifier is 2740 Ohms. Ic = 388uA, Ib = 10. 7uA, Vc = 1. 49Vdc, voltage gain = 44. 3dB, power gain = 36. 1dB Someimages taken fromthe 1957 Radio Shack Catalog are shown below. Included arelistings for the Sylvania 1N34A andRaytheon 1N66 diodes, as well as theGeneral Electric 2N107transistor. The 2N107 might have been a bargin in 1957 at $0. 99, but adjusted for inflation the equivalentcosttoday would be $7. 95. Even "low-end" electronic components were relatively dear in those days! The2N43, 43A, 44, 45 and 2N107 transistors weregraded products from the very samefabrication line. In fact, what was to become the 2N107 hadbeen discarded as rejects until the "bean counters" at GE could be convinced that electronic hobbyists mightfind them useful.

Thistransistor line was introduced in September of 1953;thefirst alloy junction devices ever produced. John Sabywas the lead developer of these historical transistors, however, the alloy junction process itself had beeninvented at GE in 1950 byHall andDunlap for use inrectifiers.

Given thesemiconductorsurfaces were not passivated, or otherwise protected from the environment, GE found it necessary to evacuate their earlytransistor envelopes to nearlyvacuum tube levels. This explains the metal "pinch" found at the top of these early "tophat" transistors. Finally, the datasheet power gain listed for the 2N107 is38dB. I`m tickled to find that my2N107 is still producing 36dB some 54 years later. Havingnow myself reached the age of 54, Ionly wish that my original "specs" would have held up so well!

Here is my Sputnik QSO Party transmitter prototype. The RF output power is 450mW with 70Vdc @ 14. 4mA on the V2 anode. The V2 screen (G2) current is 1. 6mA. The V1 anode current is 1. 05mA with 45Vdc @ 176uA at the screen (G2). These little vacuum tubes arecapable performers, however, for long-life operation it`s important toheed the maximum electroderatings as shown on the datasheets (links given below). The simple MOPA (Master-Oscillator -> Power-Amplifier) vacuum-tube radio transmitter circuit shown below was well-known in the mid-1950`s.

A crystal-controlled Pierce oscillator drives a Class-C PA. The PA grid bias is derived from rectified PA grid current (thus; never run the PA stage without the oscillator drive signal present!). The CW keying and transmit/receive switching circuitry are not shown in the circuit below. Please click here to listen to a strong-signal recording of the original Sputnik-1. The oscillator signal bleed-though during "key-up" intervals is clearly audible. This implies that the oscillator stage was allowed to run continuously. Presumably, only the power amplifier (PA) stage was keyed on/off. As such, I plan to only key my PA stage (via the anode supply or perhaps using grid-block keying). My oscillator will be switched off only while I`m receiving signals. A low-pass filter may be required between the Pi-network impedance matching circuit and the antenna. I have not yet checked the RF output spectrum, however the inherent Pi-network 2nd harmonic attenuation is only ~28dB.

The value of C1 may have to be adjusted for your particular circuit layout. This capacitor helps both to maintain the optimum level of oscillator feedback and provide the proper loading capacitance for the quartz crystal resonator. The drawing below shows the original Sputnik 1 keying plan for normal conditions; 0. 3 seconds on, 0. 3 seconds off. While the 40. 002MHz transmitter was off the 20. 005MHz transmitter was on, and vice versa. This helped to hold the battery load steady. Here`s a short video on the topic of these Soviet "Rod Tubes" (dig the Cosmonaut on the intro screen!).

Of these amazing sub-miniature vacuum tubes, Dmitri Faguet writes ( post #12 ) "The 1j24b is a universal ultra low power miniature HF pentode designed in the mid 1950`s as part of the series of so-called Rod Tubes, invented by Russian engineer and academic Valentin Avdeev, who worked at a special vacuum tube research and manufacturing plant code named No. 617 , located in Novosibirsk, Russia during and after WWII. For many years, Rod Tubes became the backbone of Soviet military and aerospace electronics, with more than 200 million Rod Tubes manufactured without any modifications for nearly four decades from 1950`s to 1990`s.

All Rod Tubes were low power battery operated pentodes with one or two thin 1. 2 V filaments, and with other rod-type electrodes rigidly located at very small distances from each other. " Back home now (and using a new D-Cell battery!). F6HKA replied to my CQ on 15/7/11. Bert began with 400w on his end but quickly dropped down to 5w. I had a perfect, 549 copy of his signal with my 20m receiver made from a diode mixer and a one-transistor audio frequency amplifier.

His, "VY FB INCREDIBLE" CW exclamation translates to a Milliwatter`s "home run. " :o) Bert emailed later, "Your 85mW doing a very nice job and your report was really 559. " We had a very solid contact lasting some ten minutes. a wonderful QRP/QRPp QSO! A total of seven 20m CW QSOs were made along the way using asingle D-cell batteryfor the entire, month-long trip. The RF ouput power was 75mW at the outset but by the time we reached Italyit had fallen to justover 50mW.

As if to compensate, the propagation improved considerably once we arrived in Italy. I first operated from a hillside just west of Perg, Austria on the 10th of June. I waspleased when ON6QP answered my CQ and we exchanged 589/529 reports. Rene was located near Liege, Belgium. On June 13 we climbed out of the Danubevalley and entered the KG rnbergerwald, just west of Linz. There we came upon the ruins of aRomanwatch tower located high above the river. The six meter square tower was thought to have been manned by a crew of six; whose duty it was tostand vigil for invaders andrelay messages using both visual and acoustic means. An earlier tower was reinforcedon this spot during theMarcomannic Wars which took place in these regions, circa A.

D. 174 (the opening battle scene inthe film, Gladiator, was supposedly set amid thisconflict). The very idea of operating my QRPp rig from the ruins of this ancient Roman signal tower sent shivers up my spine. Alas, I made no two-way contacts from this spot, however my signal was catured by two Reverse Beacon Network (RBN) stations located in Finlandand Norway!

On June 15th the Donausteig walking path led us to the ruins of SchaunbergCastle, dating from A. D. 1160. We ate our lunchin the chapel, beneath the spot where the altar must have once stood. Afterwards I flung my antenna out fromthetop of the remains of the 32 meter high tower and settled downto try my luck again on 20m CW. Again, I made no QSOs but Idid receive two RBN hits from the OH6BG receiver in Finland. Nine and a half walkingdays out of Grein, Austria we rounded a corner to find the fairy-tale city of Passau set before us.

It was a moment I shall never forget. It had been a 27km day of dodging thunderstorms; running across open fields for shelter and standing beneath farmhouse eaves munching brotchen with Milka chocolate. We had decided to splurge for two nights in a lovely hotelthatin the past had hostedboth royal families andthefirst man to walk on the moon.

Weappearedbefore the desk clerktired and muddied from the knees down. but what an adventure it had been! Three days later we met up withDL3PB and his wife in Friedrichshafen. Together we had a wonderful timeon the shore of Lake Constance until thebig hamfestwas over some days later. Thank you Peter and Petra! We took the ferry across to Romanshorn, Switzerland on a Sunday morning; arrivingat the railroad station only moments before a vintage Swiss steam locomotive pulled into the station.

What a treat!A hydrofoil took us across the length of LagoMaggioreto Arona, where our family met us for more thana week of visiting and sight-seeing. Iset up my radio twice in Italy with my10m end-fed wiredropped from the second floor balcony. On 1 July I worked G3JPX/QRP (579/449), DL1ARH (569/439) and ON4TJ (589/559). On 4July I worked DJ0GD/p/QRP. Peter was field-testing his FT817 @ 3winto a 3 meter whip antenna from Moers, near Cologne. He reported "all ok Mike no problem to copy. " Peter was 559-569 on my end. Upon my return to Vermontmy RF output power measured 52mW; down from my initial 75mW output due tothe drop in battery voltage.

AlthoughI hadn`t workedthe Americas from Europe as I had hoped, I`ve no complaints whatsoever. My thanks toW1PID, AA1MY, DL3PB and everyone else whokindly listened for my signal.