Vintage Electronics

Dan Koellen AI6XG

High Voltage DC to DC Supply Evaluation

The high voltage supply for the vacuum tube transmitter needs to be low noise in the 40 meter band, efficient for battery operation and...

Dan Koellen AI6XG

T/R Switch and QCX Interface and Modification

A Modified QCX and TR Switch for Vacuum Tube SOTA transmitter

Dan Koellen AI6XG

Single Tube SOTA Transmitter

A single tube transmitter is developed for portable and Summits on the Air (SOTA) use. The SOTA transmitter had to be relatively...

Dan Koellen AI6XG

Vacuum Tube, Battery, Lightweight, Compact, Portable: Can They Coexist?

Using vacuum tube equipment for SOTA activations? Why not! A portable battery operated vacuum tube transmitter is part of a SOTA system.

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Dan Koellen AI6XG

The Digi-Disco, a 1970's Light Controller

This is a light system that I designed and built in 1978 to control large flood lights of different colors, synchronized to disco music...

Dan Koellen AI6XG

Heathkit IT-28 Capacitor Checker

After building the Pico C-Super capacitor tester that was published in Elektor Magazine I decided to revive an old Heathkit IT-28...