This thread is very timely in that I, too, am interesting in building
a high-performance, aesthetically-pleasing tube-based AM tuner. One
which has very good output audio quality (when feeding a separate
amplifier), which will be an excellent MW DX machine, and which is
aesthetically pleasing, reminiscent of the radio chassis' of the
1930's (for example, usable in modern renditions of the classic radio
style -- a separate tube amp component would be added as needed.)

Craig's list eerily matches mine almost exactly, so there are at least
two of us in the world wanting and willing to go to all this trouble.
Anyone else here interested in the same? I've thought of creating a
Yahoo Group devoted to discussing and encouraging the design of such a
hybrid (tube/solid state) component. Would anyone even bother to join
such a group and contribute? smile/


On a semi-related topic, I am perplexed in that some say, for a newly
designed chassis, that I will not be able to find new (modern) tuning
capacitors akin to the ones of old -- that I'd have to settle for
varactor tuning. I look on the Internet and I find at least two
manufacturers who make just such tuning capacitors. They probably are
fairly expensive, even when bought in larger lots, but nevertheless
they *are* available. It would not surprise me that one could even buy
a modern tuning capacitor to workably replace a damaged one in certain
models of older radios. I see new multiple-gang 365pF tuning caps, for
example -- all over the place, actually.

The two companies I found so far which manufacture air variables
include:

Oren Elliott: http://www.orenelliottproducts.com/
Jackson Brothers: http://www.mainlinegroup.co.uk/jacksonbrothers/

Any other tuning capacitor manufacturers I missed?

(And out of curiousity, are there alternate designs for airgap tuning
capacitors besides the "meshing fin" type? I've been intrigued, mostly
for the fun of it, with a sliding tube-in-tube design -- the damn
thing should work as I think about it, should not be too big, and
because it is linear in movement (rather than rotational), will better
mechanically match a slide-rule dial.)

Comments on this?


I'm also curious to know if a varactor system can be designed which
would deliver the same level of performance as a higher-quality tuning
capacitor? I get the impression from my web research that even the
high-quality varactors are more prone to drift, are thermally more
sensitive, have higher noise levels, lower Q values, and other
anomalies that make them less desirable than comparable tuning caps.
On the other hand, I was told that properly designed and selected
varactors could reduce or eliminate the need for alignment.

Comments on this?

Thanks.

Jon