Some interesting patents

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Re: Some interesting patents

Postby (Tube_Fan) » Sun Feb 02, 2020 10:52 pm

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Joined: Wed Jun 25, 2014 5:22 pm

Re: Some interesting patents

Postby (Tube_Fan) » Sat Feb 08, 2020 3:26 pm

Posts: 349
Joined: Wed Jun 25, 2014 5:22 pm

Re: Some interesting patents

Postby (Tube_Fan) » Tue Feb 25, 2020 8:26 pm

Tubes at the USPTO

You can find a lot of audio circuits including tube based circuits in the patent collection at the USPTO (and other countries). The USPTO recently threw away their entire collection of hard copies after starting to put all of the patents on computer databases which are available on the internet and can also be searched using databases like EAST and WEST at the USPTO. Besides searching by class and subclass, you can do keyword searching using a patent database, look at other patents listed as references in patents and use patent numbers of patents you found already as keywords to find newer patents that list them as references (forward search). The USPTO and Espacenet have entire collections of patents available on the interent for free. Espacenet has US and foreign patents. EAST and WEST at the USPTO have both US and some foreign patents avaialable, but I don't know if the foreign patents are available on the USPTO web site. Companies like Micropatent have collections of patents available on the internet, but usually aren't free. There's about 80+ libraries around the country (USA) from what I remember that have facilities for doing patent searching or just looking at patents (ie. on microfilm). I heard years ago that many of these libraries had the APS computer system for searching patents. They might have EAST and WEST now, but I don't know for sure. The public can use the EAST and WEST terminals for free at the USPTO (now located in old town Alexandria, Virginia) after getting a permanent or temporary pass. Patent examiners, clerks and other USPTO employees have their own EAST, WEST and other database terminals.

To view patents go to or
Both text for later patents and images for all patents are available at the USPTO web site, but you might need a TIFF browser plug-in to view images from the USPTO. I use Alternatiff available from . Patents at Espacenet are in pdf form and require Adobe Acrobat Reader to read them, available for free at .

Since I was interested in tubed FM stereo mpx adapters I started with this subject. Searching using the keyword "stereo" in class 329 and then looking through class 381 subclasses 4, 7, 8 and 9, I found these US patents:

3167615 two triodes with diode ring modulator
3294912 transistors, detailed, shows L+R, L-R and SCA diagram
3854098 quadraphonic demodulator for records
3617641 transistor detail in IC 20
3124653 tubes, 19kHz full wave rectifier
3175040 two ring modulators, balanced
3175041 time division switching
3287501 clipper 35, diodes 31 and 32 - full wave rectification of 19 kHz signal (see column 2 lines 49+)
3209270 strange demodulator tube 20

Here's some examples of tube amps I found in class 381 subclasses 118, 119, 122 and 123:

2815407 Hafler ultralinear
2710312 Hafler ultralinear
4066975 HiFi tube, Paoli High Fidelity Consultants
2773136 Futterman OTL
2904644 voltage regulation in HiFi tube amp w/ EL34/6CA7

Some McIntosh amps:



More patents. Most are on tube audio power amplifiers.

Class 330 subclass 118

3092783 OTL
3096486 push-pull parallel
3153766 diodes -> screen grid
3566236 cathodes coupled to secondary of transformer, screen grids -> triode -> cathodes & B+
4918394 cascode input
5302912 reduced crossover distortion
5498996 plural output tubes, suppression

Class 330 subclass 119

2921266 self balancing
2919411 two phase splitters, parallel output tubes, push-pull
2595444 transformer coupling to cathodes and control grids
2918630 strange driver circuit
2833871 self balancing phase inverter
2777905 low distortion
2825766 cathode coupling, McIntosh Labs Inc.

Class 330 subclass 123

2772329 supersonic "bias" reduces crossover distortion
2934714 low distortion
3005162 VR tube -> screen grids
3138766 volume limiter/expander
4532476 two class simultaneously
4593251 two class simultaneously
Posts: 349
Joined: Wed Jun 25, 2014 5:22 pm

Re: Some interesting patents

Postby (Tube_Fan) » Sun Sep 05, 2021 8:05 pm

Posts: 349
Joined: Wed Jun 25, 2014 5:22 pm

Re: Some interesting patents

Postby (Tube_Fan) » Wed Sep 15, 2021 3:08 pm

Posts: 349
Joined: Wed Jun 25, 2014 5:22 pm


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