Amplfiers
There are currently five monoband amplifiers in a double rack cabinet, each producing 1000-1500 watts output. It's like
having an autotune Alpha -- instant band changing -- but takes up a bit more space. And the cost was considerably less than
an Alpha. I recently installed an exhaust fan above the amps to pull heat out and that made the temperature in the 12-foot
square ham shack much easier to control. The fan and blower noise is considerable when all these amps are on. A pair of noise-canceling
Heil Quiet Phones really knocks this noise down.
These amps are all homebrew, built 50-60 years ago by members of the Frankford Radio Club. I obtained most of them in
the mid-1980s. These originally included three grid-driven 4-400 amps that I recently replaced with two all-band amps using
single 4-1000 tubes in grounded grids. The photo shows the older configuration.
160 -- A single 4-1000A tube in grounded grid. Loafing at about 1000 watts output until I build up a 5KV supply
so I can get full 1500 watts.
80 -- A pair of 3-500z tubes in grounded grid.
*40 -- A pair of 4-400 tubes grid driven (now single 4-1000 GG)
*20 -- A pair 4-400 tubes grid driven (now single 4-1000 GG)
*15 -- A pair of 4-400 tubes grid driven (now single 4-1000 GG)
10 -- A single 4-1000A tube in grounded grid.
The high-voltage power supply is an old pole-pig power line transformer in a separate, small rack cabinet. A 220-volt
variac is used on the input to bring the primary voltage to about 290 volts and the supply puts out about 3800 volts.
