What are you doing here?

HR-10 is an all tube receiver. Or all “hollow state” as some like to call it. So I didn’t expect to find a transistor in there. Or two. Or a printed circuit board for that matter. But this is what I found:

Unexpected find. A PC board populated with two transistors and other components.

Situated inside the front end unit, close to the band pass filters and band switch, this is most likely a preamplifier. Two transistors in the preamp may seem like overkill and risking intermodulation and overload problems. It would make sense to either make it selectable or use it only for the higher bands, especially 15 and 10 meters that suffer from bad sensitivity in this receiver. The lower bands, especially 80 meter is filled with a high noise level and higher risk of overloading. But it seems to be permanently connected. When I get some experience with this receiver I will contemplate making the preamp switch selectable.

Based on component count and documentation I got with the equipment, this is a preamp described by W6DYD (William J. Onesky. Now SK) in CQ magazine August 1968. I couldn’t find this online after more than 60 seconds of searching. If you have a link, please comment below!

Thanks to N3RYB for contributing research for this post.

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