Tesslor R-601S Retro Vacuum Tube AM/FM Radio w/Bluetooth 3.0 Modification
For all the time I invest in researching
and writing about vintage radios of the vacuum tube variety, it is somewhat embarrassing
to admit that I still do not have an operational set, although a
Crosley 03CB console model is in the works now. I did, however,
buy a Tesslor model R-601S AM/FM radio a couple years ago in order to be able to
enjoy the warm orange glow of vacuum tubes while other projects were in the works.
The R-601S is a nice mix of the old and the new in that while it uses vacuum tubes
for the speaker preamp and output driver circuits, there is a state-of-the-art solid
state receiver front-end and tuner. I did a write-up and video tour of the
Tesslor R-601S radio in 2012. Last Fall (2013), Tesslor added
Bluetooth 3.0 wireless connectivity capability to the R-601S and offered to update
my radio. Of course I accepted and promptly shipped the set to them for a retrofit.
New R-601S models ship with the Bluetooth 3.0 feature already installed.
Upon receiving the updated radio, the first
thing I did was disconnect the stereo interface wires that had been connected from
my computer and fired up the Bluetooth function on the computer. I normally keep
the Bluetooth device discovery function turned off for security purposes, but a
quick trip to the Windows Control Panel made for an easy setup. The computer easily
found the Tesslor R-601S's new Bluetooth 3.0 module and made a successful connection.
Hooray, now I can finally get rid of yet another cable in my workspace! A few screen
shots of the setup are included, and the entire process is covered in my new
The next thing I did, of course, was remove
the back cover and take a look at the modification to see what was involved. As
you can seen in the photos, it appears a commercially available Bluetooth 3.0 module
with an integrated antenna was mated to a custom motherboard for interfacing to
the original radio circuit. DC power and a 3-wire data cable do the job. I could
not identify the Bluetooth module manufacturer since there were no identifying markings,
and a Google image search did not turn up anything. However, I could determine that
the BT IC is a Broadcom
BCM20771 stereo Bluetooth audio circuit, the flash memory is
MX25L5121E 512 kbit DIP, and there is a standard 26 MHz oscillator for
clocking. A meandering microstrip line is used for the 2.4 GHz antenna. The
motherboard's only IC is a JRC
NJM4558 dual Opamp.
The interconnect wires route into the main chassis, and I did not remove it to see
exactly where they connect.
The front panel function selector switch needs to be placed in the AUX position
for enabling Bluetooth operation. Having cables plugged into the rear panel Aux
In jacks disables Bluetooth automatically, so be sure to unplug any cables before
For the record, I
have thoroughly enjoyed my Tesslor R-601S and can unequivocally recommend it to
anyone desiring to own a bit of the past with the convenience of the present. While
my model has the vintage Phenolic look, Tesslor also offers a version with a beautiful
lacquered walnut finish (R-601SW). I would love to one one of those as well, but my budget
does not allow for it at this time (you are invited to gift one to me as you please).
Per Robert at Britta Products: "The cost
of upgrade is $60 USD and includes the return domestic shipping via UPS Ground.
That covers our costs for parts and labor and it's provided as a service to our
Tesslor Model R-601S Bluetooth
3.0 Interface Motherboard
Tesslor R-601S Vacuum Tube Radio w/Bluetooth 3.0 Modification <watch
full-size on YouTube
Note: I imply on the video that the external antennas are provided,
but in thinking about it, I believe they came with my
Sangean WR-2 radio, not the Tesslor.
Here are the specifications for the primary integrated circuit components on
the circuit boards.
The BCM2077x family
of Bluetooth system-on-a-chip (SoC) solutions targets stereo headset products. Combining
the ability to enjoy streamed stereo music with traditional Bluetooth hands-free
phone call capabilities, the chip family also provides Broadcom's leading suite
of built-in SmartAudio® technology that delivers appealing features for multiple
tiers of headsets. This is the Broadcom
BCM20771 Stereo Bluetooth Audio Chip that is targeted to single-microphone
mainstream headsets and features more advanced SmartAudio capabilities to deliver
a higher level of audio clarity for both ends of the cellular and VoIP conversation
MX25L5121E 512K-Bit [x 1] CMOS Serial Flash Memory (left)
JRC (Japan Radio Corporation)
NJM4558 Dual Operational
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 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...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.