The schematic is also available here:
Copyright © 2020 KG7TR. Technical information on this site may be shared in the interest of promoting the hobby of amateur radio. I do ask that you give proper credit to KG7TR for my equipment designs.
This photo shows the Octalmania radios stacked on top of the HB-600 linear. A 25 inch tower of 100% homebrew, vacuum tube SSB!
A technical description of the HB-600, including parts lists and schematic, is available at the button below:
Rear view. Front and back are 10.5 by 19 inch rack panels. Fan blows directly on tubes.
Top view. 572Bs deliver about 600 watts PEP with nominal 2,400 volts on the plates. PA coil is wound on a ceramic form from an old TU-5 tuning unit. High voltage board mounts caps, diodes and bleeder resistors and was made from blank fiberglass stock. Plate transformer was a brand new unit from Surplus Sales, but last time I checked their stock was exhausted.
Oblique view showing perforated aluminum covers and angle stock frame. This makes for a sturdy box. A linear's plate transformer typically weighs so much that you have to make a structurally strong unit to prevent flexing of the aluminum chassis. And of course you have to enclose the whole thing for high voltage safety. This picture was taken before the front panel was refinished.
Bottom view showing angle stock brace that runs width of chassis to beef up plate transformer mounting. Input circuits are tuned with coils wound on National XR-50 forms. The filament choke was made from an Amidon kit. A soft start circuit provides 3 second charge-up delay for the high voltage.
After completing the Octalmania radios, I wanted to build a linear so I could get on the air with a 100% homebrew station. The easiest way for me was to basically clone the design of the Heathkit SB-200, which of course uses a pair of 572Bs in grounded grid. My HB-600 is pretty much the same circuit, but obviously the mechanical construction is much different. It is styled to match the Octalmania set, and is designed so they can sit right on top of it. This amplifier was featured in the February 2012 issue of Electric Radio magazine. The front panel was later refinished and knobs changed to match the Octal Tri-Bander and 2X-813 Linear. The HB-600 linear is now owned by NU6X.
Front of amplifier. Unit covers 80, 40 and 20 meters. Meters monitor plate or grid current and high voltage.
HB-600 Linear Amplifier