K4DPK Homebrew Projects
    This little amplifier has a single 3-500Z, operates 160-10 meters and puts out a KW on all bands.  It has electronic biasing to cut the tube off between words and CW characters.  The cathode is switched electronically and the input and output RF is switched with a vacuum relay.  The power supply is a full wave bridge.  There is a digital readout for the band indicator.  This is controlled by a diode matrix, switched by one wafer of the input bandswitch.  The input networks are all Pi Net configuration, using one variable capacitor (Arco) and a slug-tuned inductor with only one fixed capacitor element on each band.  This facilitates bringing the input SWR to 1:1 on all bands.  All of the variable input components are accessible from the backplane without removing the cabinet. 

The chassis, cabinet and front panel are all homebrew from aluminum stock.  The trim around the panel and smoked plex panel is aluminum trim scrounged from an old storm window. 

Ten Tec LookALike
 

Inside the TTLA
The underchassis view shows something of a surprise....The tube socket is upside down. I did this to permit mounting the tube with a lower profile, but also (and more importantly) to allow cooling the tube pins and tube socket hardware.  A scoop situated at the lower edge of the fan scoops air and dumps it directly onto the pins below deck.
 

A Comfortable 1500 Watts
The tube that fits in that mounting plate, as some of you may know, is a 3CX5000A.  I like it because the filament requirements are so much lower in current than, say, a 4-1000.

Power supply on this one, of course, was separate.  The outdoor blower could force air up through the tube and exhaust hot air into the shack during winter, or be reversed in summer to draw air-conditioned air down through the tube and exhaust hot air outside during the summer.

This is a very stout table-top amp.

   The Tube needs no socket, being bolted directly to the machined chassis plate.
 

Pair of 4-1000As
This old amp has worked a lot of DX on 75 meters.  For a long time, the antenna was a pair of Half-Squares phased 135 degrees spaced 1/8 wave.  It's fun to work Europe in the afternoon on 75 meters.

 

 

 

 

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