(a bit OT) Tube radios
ajp166 at verizon.net
Sat Jan 2 23:50:18 CST 2010
> steve stutman wrote:
>> David Griffith wrote:
>>> Is there someone here who has built/designed an am/fm radio using
>>> currently manufactured vacuum tubes? If so, please point me in the
>>> right direction.
>> If def of "currently mfg'ed" is literal, you may have issues. Virtually
>> all the tubes which would make decent FM front ends / converters were
>> made in USA and EU; stress were.
> Count on a big box of stuff. Your best bet is to find a older 'top'
> quality tuner and rebuild it. Today's tuners are for 'cheap sound'.
> Look around, you can still get them if you shop wisely on the net.
> PS. The problem with DIY is that tube radio transformers are hard to
> come by.
Roger that. The tubes are the easy part as there is a mountain of NOS
(new unused old stock) floating around at acceptable prices. The coils
needed as well is capacitors with adequate high voltage ratings are
harder to find. You will also need resistors with .5 and 1W rating
also scarcer and more expensive.. In many parts of the circuit the
current generation metal film resistors exhibit too much inductance
compared to the older carbon composition types. The power transformer
you can plan on paying dearly, salvage from old gear or winding your own
(on a dead one salvaged).
FYI: doing a vacuum tube tuner at 88-108 mhz is as much a mechanical
project as electronic. The preferred tubes for that are the old RCA
Nuvistors (6ds4 and 6cw4 also available as NOS) but the sockets
may be a challenge. there are other tubes that do nearly s well
in the miniature basing.
If this is stereo, a stereo decoder using tubes is a ponderous afair
and none I've worked with are as good as the mid 80s or later
solid state PLL based designs. Coils for this will be hand made
if you really want to and design data will be scarce. Do try to find
a mid 1960s RCA receiving tube handbook (circuits you will need
are in the back).
The easy way, find a Dynaco or Heathkit Tuners and refurbish it.
Typically $50 in capacitors, a few tubes and they will live again.
I completed a 5 tube 3.5 to 4mhz am/ssb/cw receiver from my junk box
a few years ago. Based on current prices for the common parts it was
greater than $200 for the parts new. Heavy cost items, aluminum chassis,
power transformer (6.3V at 3A and 150V secondary), audio output
transformer, IF coils, tuning capacitors, dial assembly, tube sockets,
1/2watt resistors, forms for hand wound coils. I know this as a
friend wanted to duplicate it so I made a parts list (with acceptable
substitutions) and he priced it deciding to pass on it. He had no
old parts to draw on.
Having built and maintaining ham gear using tubes the mechanical
issues and finding suitable parts makes it difficult. While interesting
and hobby fun I can build from scratch with conventional solid state
devices faster and better radios. My junk box is not only bigger than
most it also yields a lot more 35+ year old parts!
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