I have a restored Meissner TRF AM 'HiFi'' tuner that meets your specs. It
was originally assembled sometime in the late thirties. I don't think the
special rf transformers and tuning capacitor are available now. I have never
tried it with a true HiFi amplifier but it does sound pretty good when the
output is through my son's guitar amp with the amp controls set for minimum
'çolor'....
"Jon Noring" wrote in message
...
To restate related threads, the desire is to design a "kit" so the
experienced do-it-yourself "tube-o-phile" will be able to build their
own higher-performance, tube-based AM/BCB tuner to add to their sound
system.
(At the end of this message, I'll include links to the Google archives
for the related threads.)
Such a kit would likely include ready-made PCB boards, the schematic
and parts list, and instructions/guidelines, not unlike what diytube
(see http://www.diytube.com/ ) does for their line of audiophile grade
amplifiers.
From what I would like to see in the tuner, plus what I believe the
general tube-o-phile (and not necessarily the vintage radio collector)
would want from the tuner, here is a qualitative list of requirements
(partial list, but enough for now):
1) It will be a tube-based tuner, with a line-out to plug into a
separate preamp or amp. There will be no built-in final audio
amplifier and associated speaker.
2) The audio quality at the line-out must be excellent,
clean-sounding, low noise and low distortion, faithfully resolving
whatever is in the broadcast signal.
(Obviously, AM is NOT high-fidelity, but it is important the tuner
not get in the way in whatever is there fidelity-wise.)
3) The sensitivity and selectivity, and other specs, must be
sufficiently good so the tuner, with the right antenna, will also
be able to pickup weaker stations, and not only the high-power
local stations. I would like to see the tuner be "fun" for casual
DXing when conditions are "hot" (but it is not intended to compete
with high-end communications receivers built for DXing, and used by
avid MW DXers, such as the R8B and R-75, where the DXer may try to
pickup a 1 watt station from Outer Mongolia.)
4) The design must be fairly simple, fairly foolproof for kit-building
(as much as is reasonably possible -- it is assumed the kit-builder
will be very experienced building high-grade tube equipment, or in
restoring old radios.) The number of the needed parts and
components should be kept to a minimum (particularly custom coils.)
5) It must use commercially-available electronic parts. The tubes must
be the more common ones commercially manufactured and sold today. A
comment on coils follows below.
It is important to reemphasize that the typical tube-o-phile
kit-builder will not want to, nor has experience in, scrounging for
parts from used gear. I cannot emphasize enough this point, since
over and over again it is mentioned "just hunt eBay or your flea
market for such and such a part." I can understand this sentiment
since many who frequent these newsgroups are vintage radio
collectors, who enjoy doing this, and have to do this to fix some
old radio they acquire. But many tube-o-philes prefer to order new
parts from known suppliers per the parts list, build the tuner
using the PCB board(s) the kit supplies, plug it into their audio
system, and then sit back and enjoy listening to it.
(Obviously, multiganged tuning capacitors and coils complicate
things. There are a few companies which manufacture air tuning
capacitors, and they should be utilized. The coils should be
simple enough in design so the real motivated do-it-yourselfer can
wind it themselves. But I expect the kit-originator to work with
an individual or company to build and sell the specific coils
needed for the kit so the kit-builder need not scrounge for them,
nor build themselves, if they don't want to. Are there commercially
manufactured IF coils that might be usable for the AM tube tuner?)
O.k., it seems to me the best approach is to follow what diytube has
done, which is not to reinvent the wheel, but instead find a
well-regarded commercial design from the golden years of tube radios
(the 1930's to the 1950's), and use that as the basis for the design
of the tuner kit.
(Of course, the final audio amplifier will be removed from the
circuit, and maybe a few of the parts and sections will be
modernized/upgraded as necessary to conform to the requirements.)
So, this is a call to the vintage radio collectors, MW enthusiasts
and tube experts to suggest commercial/consumer AM radio designs from
yesteryear which you believe can readily be adapted to fulfill the
listed requirements and become the basis for a reasonably
high-performance tube-based AM tuner.
What makes and models should be considered as candidates?
(Who knows, maybe a supercharged AA5 will be sufficient!)
Thanks!
Jon Noring
*****
Links to the related threads in the Google archive (Google may present
an "error" window, but should provide a link to the updated thread):
http://groups.google.com/groups?dq=&...ec.audio.tubes
http://groups.google.com/groups?dq=&...ec.audio.tubes
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