Tesslor Model R601S Vacuum Tube AM/FM Radio Teardown Report Cool Product Report
April 23, 2014 - My Tesslor R-601S is back back from the factory with an upgrade that add Bluetooth 3.0 capability and an
improved sound board. See my review of the
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
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".
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 selector knob.
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 titled, "Unlicensed 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 industrial products.
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.
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.
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.
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 6E2 "magic eye" tube that
is viewed from the front of the radio.
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 radio.
Here are the pinout diagrams for the tubes from the RadioMuseum.org
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary
purpose was to provide me with ready access to commonly needed formulas and reference material while
performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown
entity at the time and not much was available in the form of WYSIWYG
All trademarks, copyrights, patents, and other rights of ownership to images and text used on the
RF Cafe website are hereby acknowledged.