Rebuilding The Heathit AT-1 Transmitter - It's Alive!

Initial powerup tests are good and indicate that it is producing output on all four bands. I powered is up slowly with a Variac and then did some testing with an input voltage of about 110 VAC. I'm seeing output on all four bands, close to 10 Watts of output power depending on the band.

I find it is easier to adjust the driver and output controls by looking for maximum power output rather than the built in meter (the usual procedure is to adjust the driver control for a dip in the grid current and then adjust the output control for a peak in plate current - except for 80 meters where the drive
input is not tuned). The meter is an old iron vane type that is not damped and bounces all over the place until it stabilizes - which is not very good as you need to quickly adjust the controls to minimize the chances of damaging the output tube.

I still need to make some more voltage and power output measurements and look at the output waveform while keying.

I'm still also waiting for some octal plugs - one is used for an optional modulator (and needs to short two pins when not present) and one is for an optional VFO.

Heathkit sold the VF-1 VFO or Variable Frequency Oscillator that allowed it to transmitt at frequencies set by the VFO rather than fixed with crystals. I hope to acquire one of these some day - they show up on eBay quite often.

The unit could also transmit using AM voice, with an external modulator. Heathkit never offered a modulator kit, but various circuits were published at the time and in fact Heathkit published a suggested circuit in their 1955 sales flyer. It would make for an interesting project to build one - it used 5 tubes (one dual), making it a little more complex than the AT-1 transmitter.

Rebuilding The Heathit AT-1 Transmitter - Starting Assembly

Finally the tube sockets arrived, so I could get started with the actual assembly.

The new sockets were a little smaller than the originals and the mounting holes did not quite line up with the existing holes in the chassis. I cut the holes in the sockets into slots using a Dremel tool and cutoff wheel. That made it fit well enough.

As well as the tube sockets and terminal strips, I remounted the transformer and choke, front panel controls and panel.

I'm now ready to start wiring and installing the components.