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formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while typing up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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Tesslor Model R601S Vacuum Tube AM/FM Radio Teardown Report Cool Product Report
April 23, 2014 - My Tesslor R-601S is back from the factory with an upgrade
that add Bluetooth 3.0 capability and an improved sound board. See my review of
Bluetooth-enabled Tesslor R-601S with a new video.
In 1983, my wife, Melanie, gave me a 1941
vintage floor model
Crosley radio that my sister, Gayle, found in a barn on the Eastern
Shore of Maryland. It was in pretty rough shape; after totally restoring and painting
the metal parts and stripping down and refinishing the wooden parts, it looked pretty
darn good (see picture). Unfortunately, I do not have any pictures of the electronics.
Amazingly, in 1983 the local Radio Shack still had a vacuum tube tester in the store,
so I was able to identify and replace the weak ones. I got rid of the old paper
capacitors, gave everything a good look-over, then cautiously plugged it in. After
a few moments the tubes began to glow a warm orange color and the very large single
speaker began humming a 120 Hz tune. There was life in it - with no smoke!
I selected the AM button from amongst an array of shortwave bands. All the familiar
local AM stations easily tuned in, albeit with that ever-present hum. The radio's
speaker did not use a permanent magnet, but had an electromagnetic one instead;
another bad capacitor was the culprit.
Melanie and I decided to give it as a wedding
present to a relative who had a Victorian decor in the house, figuring that some
day I would find another radio and restore it. Disappointingly, that relative got
divorced and her husband took the radio and gave it to his son. All my hours of
restoration effort was gone down the drain for the sake of some guy who has probably
sold the radio by now. Since then, there has not been a lot of spare time to search
for another radio, and even if one was located, there was equally little time to
devote to a restoration project. Earlier this year I really started pining for a
vacuum tube radio. After a little poking around on eBay, it became clear that buying
something like that sight-unseen was too risky for the money people were asking
for anything in halfway decent shape. So, I began looking to determine whether anyone
offered a newly manufactured line of vacuum tube radios.
There is a surprising selection available,
but most are very expensive. The one I finally settled on was the Model R601S from
Tesslor. It has the advantage of employing a fully solid state front end and tuner,
with vacuum tubes being used in the audio output amplifier stages. A single 6N2
tube provides preamplification, and each of the left and right speaker driver channels
uses a 6P1 tube. Many serious audiophiles claim that there has never been a solid
state audio circuit designed that can faithfully replicate the "warmth" of a tube
circuit. Supposedly the mechanical vibrations within the tube elements are responsible
for the quality. My hearing is pretty darn acute (unlike my eyesight), but I cannot
claim to be able to tell the difference. My motivation is purely from a nostalgic
craving for a tube set. Oh, the R601S does have a fourth vacuum tube that is mounted
in the front of the radio case beneath the tuning dial. It is roughly the equivalent
of the old "cat's
eye" light used for fine tuning. In this case, it indicates when an FM station's
signal is being properly resolved into separate right and left channels for stereo.
If you also desire to have a fine looking tabletop electron tube radio for your
home or office, I can strongly recommend the
Tesslor Model R-601S. It has a monaural version, the
Tesslor Model R-601 (no "s" on the end). The stereo model is fairly large at
17" x 8.5" x 7", so if you have more limited space, the mono version will probably
fit at only 12" x 8.5" x 9".
Featured Product Archive
The inventions and products featured on these pages were chosen either for their
uniqueness in the RF engineering realm, or are simply awesome (or ridiculous) enough
to warrant an appearance.
If you are anything like me, you would really like to have a look at the "guts"
of the radio before making a decision whether or not to buy it. I did not have that
option, but now you do. At the risk of voiding the warranty, I opened my R-601S
and took some photos. Not only that, but to whet your appetite even more, I made
a short video showing the tubes warming up and
the "cat's eye" doing its thing during tuning.
The radio's case is a thick MDF type material with a dark, smooth, rubbed-in
finish. Cloth with a classic look covers the front of the twin speakers. The tuning
dial is illuminated from behind to produce a glowing, yellowish hue. Other than
the tuner, the only other adjustments are the on/off/volume knob and the AM/FM/FMst/AUX
On the back panel is marked the following:
"This device complies with Part 15 of the FCC Rules. Operation is subject to
the following two conditions:
(1) This device may not cause harmful interference, and
(2) this device must accept any interference received, including interference
that may cause undesired operation."
Now there is something an authentic vintage radio would not have on it. However,
it is not because Part 15 did not exist early on. According to an article I found
to Kill: A Brief History of the FCC's Part 15 Rules," Part 15 was established
way back in 1938, but did not really get much attention until a major revision was
issued in 1989 to deal with the surging popularity of RF-generating consumer and
Removal of the back panel requires loosening four screws to allow the retainer
clips to slide inward. That helps keep you from losing the screws. There is a fifth
screw which is not captive, so the designers must have figured you can afford to
lose that one as long as the others are intact. Providing for simple removal is
important because unlike the vast majority of electronics you buy these days, there
are user serviceable parts inside. That's right, the 6N2 (actually
6N2P-EV) triode and
6P1 (actually 6P1P-EV)
tetrode vacuum tubes have a rated service life of 1,000 to 2,000 hours, so if you
listen to your R601S often, be prepared to eventually replace one or more tubes.
They cost around $1.50-$2.00 each from suppliers on eBay. The 6E2 "Magic Eye" tube
costs a whopping $5.00. If you don't trust eBay vendors, you can always pay a lot
more from companies easily located with a Google search.
There really is nothing remarkable about
the printed circuit assembly, which is probably a good thing. There are lots of
connectors and wires running to and from the PCB. But, wait until you see the underside
of the chassis section that holds the vacuum tubes. With three large multi-tap transformers
reminiscent of the old tube sets, there are plenty of wires to go around. Unfortunately,
the tube bases are soldered to a printed circuit board; I was hoping to find the
traditional point-to-point wiring from each of the socket pins. Oh well, you have
to save money where you can.
As mentioned earlier, the R601S provides
not only AM and FM radio reception, but also has an auxiliary input port. I have
an audio cable running from my desktop computer over to the radio so when the mood
hits, I can fire up Rhapsody and play some moldy oldies and wax nostalgic for the
days of carefree youth-ness. Yes, a large portion of radios were transistorized
by the late 1960s and 1970s when I began really listening to music on the radio,
but I lived in a household that didn't have a color TV set until sometime in the
1970s and routinely ran out of heating oil in the winter, so we were a bit late
with technology. Tube sets were de rigueur at 114 River Road in Mayo, Maryland. In
fact, I can remember waiting for the radio to warm up in my father's 1950-something
Rambler that had a push-button transmission - in the early 1970s - and it wasn't
because he was an antique car collector.
The stars of the show are the three tubes
sitting atop the metal chassis. Silkscreening near the tubes identify the 6N2 and
6P1 part numbers, but if you notice, there are blacked out characters that alternately
call for a 6DJ8 in
place of the 6N2 and for an EL84 pentode in place of the 6P1, although it appears the
EL90 pentode is the
true equivalent. BTW, for those not familiar with vacuum tubes, the "6" at the beginning
indicates a 6.3 volt filament voltage.
To the left is a shot of the
"magic eye" tube that is viewed from the front of the radio.
Here are the pinout diagrams for the tubes from the
As mentioned earlier, I still want to eventually find another floor model tube
set, but at least now I have a high quality model, complete with a 1-year warranty,
to listen to in the mean time.
Oh, and if you love a lot of bass content in your music, you'll really love this