SCHEMATIC ONLY--MY VERSION OF 8GZ'S (L.G. WINDOM) 1925 HARTLEY X99 TRANSMITTER

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YOU ARE PURCHASING A HAND-SKETCHED SCHEMATIC ONLY OF THE TRANSMITTER IN THIS LISTING. THIS INCLUDES PART NUMBER VALUES, BUT NO STEP BY STEP CONSTRUCTION MANUAL. HOWEVER, I WILL INCLUDE A FEW OPERATING NOTES WHICH I FEEL ARE HELPFUL.
L.G. WINDOM (8GZ-8ZG) USED A SIMILAR 01A/99 HARTLEY TRANSMITTER IN 1925 TO WIN A QRP DX AWARD, BOASTING 17,000 MILES PER WATT!
MY CIRCUIT IS OBVIOUSLY NOT AN EXACT REPLICA. I'VE ADDED A FEW UPGRADES TO THE ORIGINAL. THE CIRCUIT WILL WORK WITH AN 01A OR 99 TUBE, BUT WINDOM'S FAVORITE WAS THE 99, AS HE THOUGHT THE 01A WAS JUST TOO MUCH POWER!
AT 5.5 MA PLATE CURRENT THIS 99 TUBE POWER HOUSE WILL SET THE SKIES ABLAZE WITH JUST OVER 400 MILLIWATTS INPUT TO THE ANTENNA. WITH A 400 PF OSCILLATOR CONTROL CAPACITOR THE TUNING RANGE IS ABOUT 1370 KHZ TO 4.0 MHZ, USING JUST ONE PLUG-IN COIL.
THIS LITTLE 99'ER THAT I BUILT WORKS EXACTLY AS THE ARRL 1926 ARTICLE DESCRIBED. WINDOM COOKED THE 3 VOLT 99 FILAMENT AT 4 VOLTS TO GET THE DESIRED RESULT. HE APPARENTLY FELT THIS GAVE JUST A BIT MORE POWER AND A BETTER SOUND.
I'VE TRIED ABOUT EVERY VARIATION WITH THIS RIG, INCLUDING THE 01A TUBE, AND HIS CONCLUSIONS OF 96 YEARS AGO REMAIN ABSOLUTELY TRUE TODAY--TO MY EAR THE LITTLE 99 WORKS BEST!
IN THE CIRCUIT, I'VE ADDED A FINE TUNE CAP TO THE OSCILLATOR CONTROL, AND A SERIES TUNED OUTPUT LINK TO THE ANTENNA. ADJUSTMENT OF THESE SINGLE TUBE OSCILLATOR/TRANSMITTERS IS ALWAYS CRITICAL, SO THE ANTENNA TUNING CAP REALLY HELPS. AS WITH ANY RIG OF THIS TYPE OF OPEN FRAME CONSTRUCTION, YOU'LL GET THE HAND CAPACITY EFFECT ON THE FREQUENCY. JUST PART OF THE NOVELTY OF THE 20'S ERA TRANSMITTERS.
THE LITTLE DC TO AC INVERTER POWER SUPPLY CIRCUIT YIELDS ROUGHLY 100 VOLTS OR SO, KEY DOWN, WITH THE PARTS THAT I USED.
THE NO LOAD DC OUTPUT OF THE POWER SUPPLY YIELDS WELL OVER 200 VOLTS DC. SO YOU NEED TO USE THE SAME CAUTION WITH THIS BATTERY POWERED RIG, JUST AS IF IT WERE PLUGGED INTO THE 117V AC HOUSE LINE. THIS LITTLE TRANSMITTER CAN BE LETHAL IF YOU DON'T TREAT IT WITH RESPECT!
TYPICAL OF THE HARTLEY TRANSMITTERS OF THAT ERA, YOU GET SORT OF A SING-SONG WARBLE TONE FOR THE CW SIGNAL. NOT YOUR ROCK SOLID CRYSTAL, PURE TONE CW, BUT GOOD ENOUGH TO BE ACCEPTABLE ON AIR.
WITH THE COIL SHOWN IN THE PHOTO AND A 400PF VARIABLE CAPACITOR, THIS TRANSMITTER WILL TUNE BOTH 160 AND 80 METERS (I'LL PROVIDE THE COIL SPECS). IT WILL ALSO TRANSMIT OUTSIDE THE HAM BANDS, SO BE CAREFUL WHERE YOU HAVE THE VFO SET!
IF YOU WIND ANOTHER COIL, CUTTING THE INDUCTANCE BY ABOUT 40% OR SO, IT WILL ALSO LOAD UP ON 40 METERS, BUT JUST LIKE A REGEN RADIO, THE STABILITY AND QUALITY OF THE TONE TENDS TO DEGENERATE AS YOU GO UP IN FREQUENCY.
SO IT WILL WORK ON 40 METERS WITH CAREFUL ADJUSTMENT, BUT THE TONE QUALITY IS INFERIOR TO THAT OBTAINABLE ON 160 AND 80 METERS.
THE 99 FILAMENT PULLS ONLY ABOUT 60MA CURRENT, SO THE 3.7 VOLT FILAMENT BATTERY WILL GO MANY HOURS BEFORE NEEDING A RECHARGE. HOWEVER, YOU'LL BE LUCKY TO GET MORE THAN AN HOUR OF CONTINUOUS OPERATION ON THE INVERTER BATTERY BEFORE NEEDING TO RECHARGE, AS THE KEY DOWN CURRENT RUNS ABOUT 1.5 AMPS. ADDING ANOTHER 26650 BATTERY IN PARALLEL WILL EXTEND THE RUN TIME BETWEEN THE NEED TO RECHARGE.
TO MITIGATE THE SHORT TERM LIFE OF THE INVERTER BATTERY I'VE PROVIDED A FRONT PANEL INVERTER STANDBY SWITCH, WHICH IS TOTALLY INDEPENDENT OF THE FILAMENT CIRCUIT. SO YOU CAN LET THE FILAMENT RUN, BUT ONLY SWITCH THE B+ INVERTER VOLTAGE ON WHEN READY TO TRANSMIT. THIS EXTENDS THE RUN TIME OF THE B+ INVERTER BATTERY CONSIDERABLY.
SINCE THE INVERTER USES TRANSISTORS, ITS POWER OUTPUT IS INSTANTANEOUS AND READY TO GO WHEN YOU THROW THE SWITCH. THE INVERTER IS COMPLETELY OFF IN STANDBY MODE, WITH FILAMENT ON. THE CIRCUIT REQUIRES 2X 26650 LITHIUM-ION RECHARGEABLE BATTERIES, WHICH ARE READILY AVAILABLE ON eBAY.
AGAIN, YOU ARE ONLY PURCHASING A SCHEMATIC OF THIS TRANSMITTER, NOT THE FINISHED ITEM SHOWN........KW7T
MAILING SCHEMATICS TO THE UNITED STATES ONLY