Featured Product Archive
The inventions and products featured on these pages were chosen either for their
uniqueness in the RF engineering realm, or are simply awesome (or ridiculous) enough
to warrant an appearance.
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 Just as vinyl records have made a comeback
in the last decade, so, too, have vacuum tube amplifiers and radios. Many vintage
vinyl albums from the pre-CD (compact disc) era, as well as from groups in the 1990s
and early 2000s (most from the latter group I have never heard of), are
being pressed again. In fact, companies are having a hard time keeping up with
demand. Melanie and I have a respectable collection of original 45 rpm Singles
and 33-1/3 rpm LPs (long-playing) records from groups in the 1960s through
early 1980s, that is to say, up through our
tweens
and early twenties ... but I digress.
With 3.5mm AUX input and 3.5mm headphone jack output, can be
used as a headphone amp and a stereo preamp, compatible with most audio source such
as MP3, iPod, phone, tablet, computer, CD player etc. and output can connect headphone,
amplifier, active speaker etc. to greatly improve the sound quality. Adopting classic
6N3 vacuum tube to effectively eliminate the harsh digital sound, providing HiFi
clear, soft and smooth, warm and sweet tube sound. The sound field is wide, especially
suitable for vocals, strings, light music, classical music, etc. Adopting solid
state design, preamp part uses vacuum tube for amplification to make the input audio
signal more natural with high dynamic range, and amp part uses NE5532P op amp to
ensure the speed and power of audio signal transmission.
Not only as a headphone amplifier, compatible with wide impedance
range (12-200Ω), but also as a preamp for your other power amplifier, convenient
and efficient to improve sound quality. 1*3.5 mm stereo jack input, can be connected
to computer, CD, mobile phone and lossless player. 2*3.5 mm output can also be connected
to digital amplifiers and active multimedia audio devices. Default Beijing FU32
vacuum tube, can be upgraded to GU-32/832; Default NE5532 op amp, can be upgraded
to OPA2604, JRC4558, OPA2132, OP275 and so on for enjoying different tones.
What inspired this article is having just seen a Google Ad here on RF Cafe promoting
a Mini Vacuum Tube Headphone Amplifier (see screen capture to the left). By Google's
rules, I can't click on it to see where it leads because it would be considered
a fraudulent click that costs the advertiser money. I did a search on Amazon and
found what appears to be the same thing. However, the vendor there wants more than
$300, whereas identical
Mini Vacuum Tube Headset Amplifier models can be had on eBay for under $50 (image
on right). It uses a 6N3
duotriode tube (inexpensive and easily replaced), which helps ensure matching
characteristics between the left and right channels. Cathode voltage is 150 V,
so it needs to convert the 12 Vdc input to 150 V.
That is a pretty basic stereo amplifier with a more modern look. If you want
a real conversation piece that looks like a retro section of a radar, then you'll
want to opt for this Little Bear
Vacuum Tube Headphone Amplifier. They should consider branding it with a more
eloquent name like the Ursa Minor
Vacuum Tube Amplifier. That FU-32 vacuum tube is the very definition of "way cool."
It is evidently an equivalent of the
RCA 832 tube, which can be bought on eBay for under $10. You can bet if
I had a spare $80 in my pocket, I'd be getting me a Little Bear.
Finally, if you need a wireless amplifier to feed speakers across the room, back
yard, garage, or basement, consider something like this
vacuum tube Bluetooth stereo amplifier.
I couldn't find a WiFi-connected version. Dozens of designs are available for both
wired and wireless vacuum tube
stereo amplifiers.
Posted August 10, 2023
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