3-throw switches, octavation & tubesynth

[Bill Layer]

Hi All,

This reply was prompted by an earlier posting re: "3-throw" switches, but
has application specific to the EB tubesynth VCO.

One 'common' form of the 3-throw switch is the old-fashioned 'DP projector'
style which has the following states:

	1) Down - Off
	2) Mid - circuit 1 on
	3) Up - circuits 1 and 2 on

In a VCO that is frequency dependent on a simple R-C time constant (read:
EB's thyratron VCO) this type of switch used in conjunction with 3 matched
capacitors can be used to provide a very neat 3-octave (low-med-hi) range
switch, by using the seperate circuits to switch a series-parallel cap bank.

The accuracy of the octavation is depenent entirely on the accuracy of the
cap matching, which can be very good. Obviously, low-dissipation
factors/leakage are very helpful. I can provide a simple schematic for
anyone interested.

A note on matching small value caps: DO NOT handle them prior to or during
the matching process, if at all possible. Minute temp changes from your
body will play havoc with the readings, make for a poor match, and waste
huge amounts of your time.

------------------------------
Bill Layer
Sales Technician

Viking Electronics, Inc.
1531 Industrial St.
Hudson, WI 54016

Phone: (715)386-8861 Ext. 210
Fax: (715)386-4344
E-mail: b.layer at vikingelectronics.com

http://www.vikingelectronics.com
24 Hour Fax Back System: (715)386-4345