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PHILCO PHORUM

It is normal for the off-on-band switch in Philco models 19 and 89 (plus early versions of Model 14 and late versions of Model 91) to be defective after 70 plus years of operation.

Fortunately, a replacement which works extremely well is readily available from Mouser Electronics. It is part number 10WA326 and is a three pole SHORTING rotary switch which is user adjustable from one to four positions.

UPDATE: The 10WA326 switch is no longer available from Mouser. A switch that is similar, but with PC terminals (part no. 10WA346) is still available, and the connections are the same as shown in the diagram below.

Why a shorting switch? It is important that while in operation, when switching from AM to the old "police" band that the set remain on. With a non-shorting switch, the contacts "break" before they "make". In other words, the contacts are temporarily disconnected before making contact with the next set of contacts.

A shorting switch makes contact before it breaks contact with the previous set of contacts. This is important insomuch as the AC is fed through one set of contacts, and it is not desirable to temporarily turn the set off while switching from AM to "police". The non-shorting switch introduces an objectionable "pop" while changing bands; the shorting switch does not have this problem as the contacts carrying AC are, in essence, only disconnected when the set is turned off.

The replacement switch (shown in schematic form below), is basically a switch which can be adjusted from two to four positions. For use in Models 14 (early), 19, 89 & 91, it needs to be set as a three position switch, with the fourth position locked out and not used. To accomplish this, remove the mounting nut and lockwasher from the switch and set the locking ring under the lockwasher into the proper position to make the switch a three-position switch. (The switch comes with a diagram showing exactly how this is done.)

The shaft is flatted correctly to accept the Philco knob, and is about the right length for Models 14 & 91, but will be a bit too long for Models 19 and 89 - you will need to shorten the shaft by about a quarter of an inch or so for the 19 and 89 sets. Compare its length with the volume control and tone control shafts to see just how much of the shaft to remove before cutting, to avoid cutting off too much shaft.

Looking at the diagram below, you will note that each terminal is numbered. This shows you how to hook the new switch into the circuit. There is usually enough wire in the original circuit so that the switch may be connected and put in place without difficulty. If this schematic is followed exactly as shown, the switch will perform as the original.

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© 1997-2006, Ron Ramirez. All rights reserved. Unauthorized duplication prohibited.