Power supply caps are (4) 100uF in series.
The bridge is full wave with (4 )silicone diodes per leg. Peak current draw is stated at 16.7 amps. The power supply is 120VAC input only, and not configurable for 240 VAC operation. The amp will operate fine without the external cut-off bias, but will dissipate ~250w during idle. 100 volts external bias is required to idle the amplifier during receive. The amplifier features fixed internal bias with external stand-by cut-off if desired. I chose to retain the original relay and use an isolated amp interface. The original keying relay is 120VAC and externally engaged so some modified keying arrangement must be made. The tuner method is OK for testing but adding a permanent input tank is the way to go for permanent use. Bear in mind that there will be reactive currents flowing along the outside of the coax between the tuner and the amp so keep the coax length short and arrange sensitive equipment away from this stray RF. Tune up the amp next, then tweak the input again to get rid of any remaining reflection. If you choose the later, try tuning into a 50 ohm dummy load with the amp out of the circuit first each time you switch bands. You can build one or use a tuner between the amp and the exciter. This amp was not designed with a tuned input circuit so use with modern solid state transceivers requires a tank circuit of some type to be employed between the exciter and the amplifier. Typical peak output power with new tubes in my unit varied from 600w-900w depending on band.Īs with most amplifiers of this vintage two modifications are essential for use with modern solid state transceivers – a tuned input network and a low voltage keying relay. Advertised gain is 10db with short duration PEP output of 1000w. The amplifier model 3340 input power is rated at: 1500w SSB, 1000w CW, or 400w AM.
Some later models, designated MKIII (?) were equipped with (4) 572B finals.
This 1960’s vintage amplifier, model 3340 utilizes (4) 811A triodes in parallel, grounded-grid configuration.
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