One-valve transmitter for 7 MHz

 

Fig. 1. Valve transmitter.

Building this transmitter was inspired by an article in "Popular Electronics" 2/1955. The circuit diagram is simple, and the valve (6AQ5) can still be purchased. So I decided to build the project.

Fig. 2. Circuit diagram.

I find the circuit diagram clever. C6 and L3 are mounted on top of the chassis, and may be touched by the operator. However, the B+ voltage is neither available at the variable capacitor C6 nor at the coil L3. This is because C5 isolates the two components from B+, and they are both grounded. This precaution increases electrical safety.

High voltage is present at the bottom of the chassis. I decided to cover all components with high-voltage by plexiglass to avoid danger of electrical shock. 

Fig. 3. Top view.

Fig. 4. Bottom view. Note the plexiglass walls. 

The power supply is unregulated. When current is drawn during transmit, the B+ goes down from 215 V to 185 V, and this reduces the transmitter output to 2 W.

Fig. 5. Power supply for the transmitter.

I wish you a happy New Year, and hope for better times next year without corona-virus!

73 OZ1BXM Lars

Homepage: oz1bxm.dk