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Re: True Vibrato varistors

8/30/1997 3:44 AM
R.G. Re: True Vibrato varistors
forgot to ask - what's the date on the patent?
8/30/1997 6:08 AM
Tony T

The patent number is 2,988,706. D.L. Bonham is the name on the patent. It's dated June 13, 1961 and filed on October 29, 1958. VIBRATO CIRCUIT COMPRISING A BRIDGE HAVING NON-LINEAR IMPEDANCE ELEMENTS is the title. Can you belive it cost only $3.00 for a copy (all 5 pages) and it only took about a week to get it! Our federal government at work (U.S. States Department of Commerce, Patent and Trademark Office). The phone number is (703)305-8716 in Washington, D.C.  
Internet site is:  
If that's to much trouble I can fax you a copy on Tuesday. It's the least I can do for all the help you give us here, not to mention those awesome AC128 fuzz face boards I got from you back  
in June!
8/30/1997 11:57 AM
Thanks for the offer, but I'll just order a copy. I didn't know that there was a single original patent on it. This dovetails into the work I have going (well, OK, stalled because of work pressures) on an all-tube phaser.  
From the title I suspect that the patent made a big deal out of the "bridge" nature of the Magnatone circuit. The bridge setup is primarily to cancel out the 70V or so swing of the LFO that they needed to change the resistance of the varistors. That's the real problem with those varistors, btw. It takes a BIG change in voltage to make them change resistance.  
Glad the boards are working well for you.
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