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
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
Bluetooth-enabled Tesslor R-601S video.
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 a Macronix
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).
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 customers. "
Model R-601S Bluetooth 3.0 Interface Motherboard
Tesslor R-601S Vacuum Tube Radio w/Bluetooth 3.0 Modification <watch
full-size on YouTube website>
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
MX25L5121E 512K-Bit [x 1] CMOS Serial Flash Memory (left)
JRC (Japan Radio Corporation) NJM4558
Dual Operational Amplifier (right)
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