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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 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 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. "
Download the Tesslor R-601S Owner's Manual
Download the Tesslor R-601S Bluetooth Manual
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 conversation
Macronix MX25L5121E 512K-Bit [x 1] CMOS Serial Flash Memory (left)
JRC (Japan Radio Corporation) NJM4558 Dual Operational Amplifier (right)
Tesslor R-601S Retro
Vacuum Tube AM/FM Radio w/Bluetooth 3.0 Modification
- Tesslor R-601S Vacuum Tube Radio Teardown
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Posted April 23, 2014