|Tubes & Valves ~ A CW Transmitter|
|PDF Copy of the Presentation to the G-QRP Virtual Convention ~ September 4, 2021|
The purpose of these web pages is to supplement the presentation to The G-QRP Club Virtual Convention held September 4/5, 2021. These pages cover simple vacuum tube Transmitters that graced many shacks during the 1930-1960's. Simple they may be; but they are fully capable of communicating over great distances.
Foremost is Safety as there are High Voltages present and more than one ham has succumbed to death by High Voltage. The One Hand Rule must be observed. Simply stated one hand behind your back as you poke or prod the innards of any rig.
This also extends to simple things like having shielding around anything with high voltage present and avoid metering in the High Voltage circuit. A meter inserted in the Cathode return works just as well and even better is to have a sampling of the RF output. That sample can be calibrated to show maximum output. Clever hams can hand calibrate that meter scale to read Watts output!
Our research in preparation for the presentation looked at published schematics from sources like QST. Sadly those schematics are "just not up to snuff" for operation on today's bands! Typically QST failed to include fuses in the main power supply circuitry likely reasoning the transmitting tube WAS the fuse. The power supply filtering is marginal at best. The lack of basic design protocols surely added to the din of cacophony of chirpy, drifty and clicky signals blanketing the bands during the 1930-1960's. . Today that simply is not acceptable!
Our goal should be to have a Clean Signal that is done Safely with the Safety built in from the outset. IF IT IS BUILT RIGHT, IT WILL WORK RIGHT!
A 6V6 Valve Transmitter on 40M
For 300 VDC Make the 15K Resistor 2 Watts. Install a 2.5 millihenry RF Choke to Ground following the 900 PF variable (HV Glitch Protection).
Some added safety Features ~ The chassis back and front are enclosed in metal
Construction of a 350VDC Power Suppy