- 2025
- Jan
- 28
The Heatkit AF-1 Analog Frequency Meter, Intermission.
One of the things I’ve been considering with the Heathkit AF-1 I have on the bench right now is the potentiometers. The originals were 200Ω wirewound rheostats, but the original owner of the device replaced some with 5kΩ carbons. No idea why.
Future me note: I’m not sure what went on at Heathkit, but this device went through some revisions before being released to the general public. Perhaps it was released before full testing had finished, but it appears that even when new the device didn’t quite perform correctly with the included parts. The original owner attempted to correct these failings, but needed a bit more dial-out range in some spots. The good quality, stable parts we have available today certainly help here as well!
New parts will bring increase the precision of the device (as much as you can with an analog meter of this type!) so I’m torn. Leave the old parts in place and assume the original builder knew what he was doing, or get new 200Ω devices.
I didn’t leave the old parts there. New 10-turn wirewound potentiometers made this thing easy to dial in.
The blue pot in the foreground is a 10-turn, 2W, 200Ω device. These are relatively cheap (~$2) if you buy them direct, so I picked up a couple. One 200Ω, one 5kΩ. I’m planning on restoring the power supply on this device first, so I’ll put one in circuit and see how it does.
Of course, the only problem is they are the finest chinesium. They say Bourns on the bottom, and they probably were based upon that device. Will they hold up? I don’t plan on using this device a whole bunch, but stay tuned and we’ll find out!
Next part of this series: https://wereboar.com … -different-approach/
Previous part of this series: https://wereboar.com … -meter-part-4-parts/