On Wed, 20 Apr 2016, Geoffrey S. Mendelson wrote:

Michael Black wrote:
I gather those with HRO-500s have had some problem replacing germanium
transistors (and probably the germanium transistors need replacing because
they've gone bad over time).


Germanium transistors are cheap and plentiful on eBay. You need to figure
out which ones made in the Soviet Union replace the ones made in the west.

Germanium transistors were mostly PNP, so NPN ones are harder to find.

Replacements for CK722, 2n404, 2n107 and 2n109 are less than a $.25 each
including postage. I am sure there are others, but those were the ones
I needed.

At least some of those are audio bandwidth transistors, the HRO-500 of
course needs transistors good in the shortwave and low VHF segment.

I just know I've seen people writing about restoring their HRO-500s and
other things with germanium diodes, and getting replacements has been some
sort of an issue.

I probably have some germanium transistors around, unless I tossed them.
There was a period in the seventies when the local electronic store, which
also sold surplus (Etco Electronics, they later moved their base to the US
to do mailorder) was offering great deals on germanium transistors, but
their selling point wasn't that they were germanium. It was that they had
good frequency response. I did buy a lot of those back then.

In some ways it is a surprise the HRO-500 could come out in 1964. It's
not that long before that transistors were for audio and at best the AM
broadcast band, yet here is a receiver that from reports is fairly good,
it wasn't a consumer radio, but which could be transistorized. The big
wave of transistor shortwave receivers came towards the end of the
sixties, and some, like my Hallicrafters S-120A, were awful, in part
because they were transistorized. Lots of overload, on top of the usual
issues related to low end receivers.

Michael