Rebuilding The Heathit AT-1 Transmitter - Testing and Wrapup

I did further testing of the restored unit, measuring voltages against the manual, and they all looked okay.

The unit was speced at operating from 105 to 125 VAC. At the time it was released line voltages in North America tended to be lower than today (typical 120 VAC or more now). For testing purposes I found that an input voltage of 117 VAC gave heater (6.3 VAC) and B+ voltages that were close to what was listed in the manual, so I did my testing with a Variac set to that level.

I measured the RF output on each band both with a rather inaccurate SWR/power meter and by measuring the peak to peak output voltage on an oscilloscope across a 50 Ohm dummy load.

    80M: 13 Watts
    40M: 12 Watts
    20M:6.3 Watts
    10M: 1 Watt

Power on 10 meter is quite low, but is apparently normal as the output tube has very low gain at the higher frequency. I captured the output on different bands on my oscilloscope:

Since the power supply is not regulated, there is quite a drop in the B+ on key down, from 512 to 430 volts. Note that there is also 139 VDC at the code key contacts, so you want to avoid touching them!

Here is the oscilloscope output of keying:

And using the spectrum analyzer mode of my Rigol scope:

It is interesting compare some of circuitry before:

and after restoration:

This project was a lot of fun - I got to recreate the experience of building from a kit. I was also fascinating think that someone built this in the late 50s or early 60s and obviously used it quite heavily over the years.

I will have to try it on the air once I get an new antenna up. The power level qualifies it as a QRP rig.

I'm still looking to find the VF-1 matching VFO if I can get one at a reasonable price.

Rebuilding The Heathit AT-1 Transmitter - Final Amplifier Tube Wiring

I finished up the next set of assembly instructions  - the wiring around the final amplifier tube.

The last toroid is another large one that is too heavy to stand in the air by its leads. so I sat it on the chassis. As this has some high voltage (close to 1000 volts), I wrapped it in electrical tape to better insulate it from the chassis.

Next up is the assembly of the coils, much of which will use heavy bus wire and be on the top of the chassis.

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.

Heathkit RX-1 Recapping

I finished "recapping", i.e. replacing the paper capacitors in the Heathkit RX-1. Some were a little tricky to get at when the unit was assembled.

Here are some of the original caps:

And here is an image after recapping (the news ones are all yellow):



I didn't notice any significant difference after recapping, but it is still a good idea to do. Depending on the circuit location, a leaky capacitor can damage a tube or other expensive component. Below is all the old caps after removal: