[600MRG] Homebrew Tube Transmitter

[Michael Mussler]

Goody,
It is feasible to convert HF tube rigs to the new 630m band. Paul W0RW modified an old DX-100 for use on 600m. I modified a home-brew 2m amplifier for 630m service that runs a pair of 6146 tubes in the PA. 

In addition to reworking the grid and plate tank circuits I replaced the plate choke with something more appropriate to the 630m band (4 mH, > 200mA) and scaled up the values of the coupling and bypass capacitors. The cabinet dimensions will prove to be a limiting factor. Consider use of iron powder core toroids in place of air wound coils for the plate and grid circuits to solve the space problem. I had success with Amidon red cores (T-225A-2). Select a core size that can handle the current levels involved. Running about 120 watts input the core I use remains relatively cool. 

The vacuum tube approach is less efficient than the solid state devices many are using, but on the plus side tubes are relatively forgiving of antenna VSWR changes. I’ve got over 20,000 hours on this amplifier in WSPR and beacon service. 

Good luck and hope to hear you on the new bands!
73
Mike, AI8Z
ex WD2XSH/12