Sputnik QSO Party Transmitter Prototype

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 are capable performers, however, for long-life operation it's important to heed the maximum electrode ratings 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. 

Parts List

C1:     85pF S.M.

C2:   100pF S.M., 100V

C5: 1000pF, 100V

C6:     10nF

C3,4,7:  10nF, 100V

C8:    2200pF, 250V

R1:    27k

R2:    68k

R3:   100k

L1,2:  67uH 

L3:  3.3uH

VC1:   5-35pF

VC2:   20-150pF

X1:  21.060MHz, ESS Type HC49

V1:  1sh24b (1j24b or 1Ж24Б) ex-Soviet sub-miniature "rod tube"

V2:  1p24b  (1П24Б)      "                     "                      "

Notes: 

1. Ground the internal shields (V1 pin 3 and V2 pin 4)
2. 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.
3. 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.
4. I had somewhat better results with V2 pin 1 (the filament common terminal) negatively polarized. 

 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.

 

DL3JIN has made a wonderful job of his Sputnik Sender; details of which may be found here. Well done, Peter!

Roger, G3XBM and Andrew, G6ALB posted details of their Sputnik-1 transmitter project here. 

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."

David, NM0S, is building his Sputnik clone into a metal earth-globe. How clever!

 

Links

Sputnik-1 and Amateur Radio
Sputnik Declassified: Nova, 2007 documentary
Spaceflight Magazine: Vol 49 November 2007 
Volkssternwarte Muenchen; thanks to DL4ZAO for the excellent link!
Sputnik Model Plans; from The Arizona Model Aircrafters 
October Sky (required viewing for Sputnik QSO Party participants ;o)
The Top Ten Sputniks
Dr. Asif Siddiqi's Research Pages; my thanks to Chris, OE3HBW
More Sputnik-1 Info; Tnx to OE3HBW
Pull Apart the PS-1; Tnx to OE3HBW