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Old 6th March 2006, 04:19 PM   #1
7n7is is offline 7n7is
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Post tube patents

Here's list of patents disclosing various tube circuits and how to look them up.

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Old 24th April 2007, 08:59 PM   #2
7n7is is offline 7n7is
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The forum's gone. This was in the thread on the other forum.

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 http://patft.uspto.gov/netahtml/PTO/srchnum.htm or http://gb.espacenet.com
Both text for later patents and images for all patents are available at the USPTO web site, but you need a TIFF browser plug-in to view images from the USPTO. I use Alternatiff available from http://www.alternatiff.com . Patents at Espacenet are in pdf form and require Adobe Acrobat Reader to read them, available for free at http://www.adobe.com .

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:


It might be easier for beginners to use http://gb.espacenet.com and put in the patent number preceded with "US", ie. US3167615, under "View a patent application". You need to have Adobe Acrobat Reader installed to view the patents. Click the patent number on the pages that come up and eventually you will get to the pdf images.


You can also link directly to the patent like this:



You can look up classes and subclasses here:

class 329:

Class 381:

Class 330:



Another thing I should say is that you have to have Javascript on to use http://gb.espacenet.com/
Just put the patent number (for example US3287501) in the second doohicky, click GO and click the patent number in the pages that come up to get to the pdf images.


One thing I forgot to mention is that patents issued more than 17 years ago are expired. They changed the law sometime in the 1990's to 20 years from the filing date for patents issued since then. All the patent numbers I posted are for patents that are expired and in the public domain. Maintenance fees have to be payed from time to time for patents that aren't expired. If the fees aren't payed then the patents become expired. There is a grace period where if the fees are payed then the patent is in force again. If the fees aren't payed within this grace period then the patent becomes expired forever unless there is an act of Congress which isn't likely.


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
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Old 24th April 2007, 09:01 PM   #3
7n7is is offline 7n7is
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Another link for patents: http://www.pat2pdf.org
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Old 24th April 2007, 09:14 PM   #4
tomtt is offline tomtt
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thanks for the links.

Originally posted by 7n7is

The forum's gone. This was in the thread on the other forum.

here again

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Old 24th April 2007, 09:35 PM   #5
7n7is is offline 7n7is
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I can't find the orginal thread in that forum. Here's the Google cache version.
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Old 24th April 2007, 10:51 PM   #6
Eli Duttman is offline Eli Duttman  United States
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DECWARE upgraded their BBS software and the URL changed.

The DECWARE BBS is here.
Eli D.
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Old 29th March 2010, 02:11 PM   #7
7n7is is offline 7n7is
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See also Google Patents
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Old 2nd April 2010, 12:16 PM   #8
banat is offline banat  Serbia
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Google patent:Method to exerciting a Cat, Thats cool one(ha ha).Click the image to open in full size.
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Old 24th January 2011, 12:57 PM   #9
7n7is is offline 7n7is
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More useful information.

Millions of hard copies of patents took up a lot of space at the USPTO. They threw them all away years ago and put them all on databases.
Flickr: Crystal City, Beltsville & College Park's Photostream

Sciencemadness - Multi-page TIFF files
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Old 24th January 2011, 02:37 PM   #10
richwalters is offline richwalters
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Murderous trying to find on this....
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