WB6TNL: A different take on cathode keying

Steve Smith, WB6TNL, of Oxnard, CA, writes that “in a typical cathode-keyed ‘glowbug’ circuit, the tube is self-biased to cutoff. Only the cutoff voltage appears at the key terminals. This is typically 50 volts, or so. Not exactly comfortable if contacted but not nearly as dangerous as full B+ on the terminals. This is true even in a (higher voltage) 6146 example.

“(In the L’il Buddy), the 47K resistor (from the grid to ground) should cut the tube off just fine, key-up.

“I’ll build the rig and send you a picture. This will be an interesting experiment for the following reasons:

“Since the tube was designed – per RCA – ‘especially for wavelengths between 0.5 meter and 5 meters,’ on HF, this might be one instance where the performance improves as the frequency increases.

“It will be interesting to see what the spectral purity looks like right at the (coil) link.

“Spacing the link below the tank winding probably won’t match to 50-ohms very well. Either a link coupling variable capacitor, a following antenna tuning unit or winding the link over top of the tank coil may be required to get to 50-ohms.

“Hmmmm . . . 9-volt batteries are two for a buck at the Dollar Store. Eight bucks will give me 144-volts. I've got a 955 or two in the junque box. This might be just the ticket for ‘Show and Tell’ at QRPacificon.

“This will be my first project using an ACORN tube so it should be fun.”