RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
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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
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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
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
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 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
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 trying it.
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 customers. "
Tesslor Model R-601S Bluetooth
3.0 Interface Motherboard
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.
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)
Dual Operational Amplifier (right)