Restoring a Prototype HT-18
by Ken Ketner KA5ELD

Ketner's descriptions of the HT18 and work on it.

Front View of the HT-18 Prototype.

I received 2 HT18 sets hoping to get one good one. Now it looks like

there will be two, and perhaps an interesting development with one of

them. When I began working on the first one, I noticed that there were

machinist's scribe marks all over the chassis, marking drill holes, no

screened labels on tube sockets or terminals, different knobs on the

front panel, different colored dial pointer (yellow), and slight

variations in cabinet mounting screws. The other presumably standard

unit had no scribe marks, had screened tube socket and terminal labels

on the chassis, had a red dial pointer, and the standard set of knobs.

This led me to suspect that the one I had begun restoring was a

prototype of some sort. So I set about cleaning and lubing it, and

placing it into working order without any noticeable changes from the

condition received.

Inside Top View of the HT-18 Prototype. Click here to enlarge image.

Under chassis I replaced about 4 wax paper caps and disconnected the

can capacitor because it tested bad (but I left it on the chassis) and

installed 2 axial lead electrolytic caps, installed a new power cord

through a neoprene grommet, put in a good set of tubes. I cleaned up a

few ground connections and a few iffy looking solder joints. I then

brought it up slowly on my variac. When at working voltage I got 5 watts

into a dummy load on 7mhz, so it seems to be working ok. There are no

topside or outside mods visible on the unit.

Rear View of the HT-18 Prototype. Click here to enlarge image.

The second HT-18 is surely a production unit, and it seems

restorable, so I will probably go ahead and bring it up to speed soon.

- Ken Ketner, KA5ELD,

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