"Richard Knoppow" wrote in message
...
"gareth" wrote in message
...
Further information most welcome, thank-you
In the 1948 Radio handbook which I mentioned previously, there are
adverts
from a company by the name of Millen, and I assumed it was the same guy
after he had left National.
Your comment about a phenolic intersperser is no doubt some means of
isolating an
earthy contact?
It would be interesting to know from the Lamb patent whether he proposed
therein the
technique of Single Signal Reception by the use of the phasing control to
null
out the audio image, or whether this was something that came about
through experience?

I think this was part of Lamb's original intention. The articles
originally describing the use of the filter were aimed at "single signal"
reception, meaning that the audio image was suppressed. The Lamb filter
required some juggling between the bandwidth and phasing adjustments to
get the response to where the operator wanted it since they interacted
with each other and with the center frequency. Nonetheless, the filter
worked very well and provided an order of magnitude better selectivity
than was available previously.
James Millen was one of the founders of National but eventually was
pushed out of the company. He started his own company, also in Malden
Mass, and probably made many parts for National as well as his own stuff.
Millen made very high quality components. There is considerable history
of both National and Millen, including a Millen Society, on the web, a
Google search will find it.
The National HRO was a revolutionary receiver in its day and stayed one
of the favorites for both ham and commercial use for some thirty years.
The mechanical design is attributed mostly to James Millen and the
electronic design mostly to Herbert Hoover Jr., son of the president of
the US.


I'm in the process of making a retro RX, primarily because I've a junk box
going back
50 years and if I don't do something with the bits now, then the executor of
my will
is likely to skip the lot.

I recently analysed the Sperry PWD dial from the HRO, and conceived of a way
to
reproduce it, but without needing an internal toother ring.

However, my tastes have changed, and I'm now heading for an RX that is
similar in style
to the Eddystone EA12.

But the one thing that I owe to the National design in my musings is the
possibility of
emulating the Catacomb from the NC100X RX, as the means of simplifying the
wiring
of a bandswitch.

I was originally interested in the variable selectivity of the Eddystone,
and, indeed, have obtained
a photo of the innards of one of the variable IF transformers, but I think
that I'll do a coouple of ladder
filters based on modern practice, with both SSB and CW versions.

Once again, very interesting articles from you, thanks!

Gareth G4SDW