Antique Electronics and Vintage Solid State

Eico 320 Signal Generator Restoration

I’ve taken a liking to the blue art deco paint scheme on Eico’s old test equipment.

IMG 7636.jpg

This Eico Model 320 signal generator is a good example. 

IMG 7634.jpg

Internally, it is a very basic two-tube signal generator, with a 6X5 rectifier and a 6SN7 dual triode. …

Heathkit IM-28 VTVM Restoration

I recently restored a Heathkit IM-28 VTVM.

IMG 7624.jpg

I had always wanted Heathkit’s IM-13 bench model VTVM. The IM-28 is the “new look” version of the IM-13, and I couldn’t pass it by when I saw it at the MIT Flea.

Homebrew Switchable VTVM Probe

Here’s my homebrew switchable VTVM probe.

IMG 7631.jpg

This one was made up for a Heathkit IM-28.

IMG 7610.jpg

I used a tiny SPDT slide switch I purchased some time ago from Electronics Goldmine, a 1 MΩ resistor, and a scrap of Vector board to put together the switching circuit.

Switchable VTVM Probes

Many popular VTVMs used a switchable probe: a probe that contains a one megohm resistor for DC measurements, and a switch to bypass the resistor for AC and Ohms measurements.

IMG 7652.jpg

For example, here is the classic Heathkit probe from my IM-11 VTVM.

© Steve Byan 2011-2019