Philco mod 49-906 band switch

12/23/2010 3:00:40 PMMitch

Hello all,
I need a new or used am fm band switch. This switch is very odd in design and i have been on many web sites trying to find one that will work.
It has 4 double contact poles, 3 being used. It is a shorted type where am switches to fm with make before break. A standard rotary switch won't work.
I really need some help on this.
Thank you.
Mitch

12/23/2010 3:11:03 PMWarren

Might try an old computer data switch box. The rotary switch can be just A & B or some have A-B-C-D .. The switch has multiple contact points, but can be wired to fit your needs.

12/23/2010 3:37:35 PMEdd

Sir Mitch. . . . .

I am schematically evaluating that switch as only having TWO separate A and B active sections.

One section is a spdt rotary action that switches B+ for the AM-FM transitioning.

The other section is also a spdt rotary action that switches audio level signals .

You may have some reeeeaaaal Wierd Albert mechanical construction, on that unit, but only the above switching basics are the ones that need to be met.

As per the consideration of the shorting . . . .e.g . . . make before break action . . . versus . . . non shorting type of switch . . .that is no real problem .

If using a non shorting type, you will merely have a quick "pop" during band transition on the radio . . . . IF being running while doing the band switching.

73's de Edd

Might try an old computer data switch box. The rotary switch can be just A & B or some have A-B-C-D .. The switch has multiple contact points, but can be wired to fit your needs.
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12/23/2010 7:31:30 PMMitch

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:Sir Mitch. . . . .
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:I am schematically evaluating that switch as only having TWO separate A and B active sections.
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:One section is a spdt rotary action that switches B+ for the AM-FM transitioning.
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:The other section is also a spdt rotary action that switches audio level signals .
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:You may have some reeeeaaaal Wierd Albert mechanical construction, on that unit, but only the above switching basics are the ones that need to be met.
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:As per the consideration of the shorting . . . .e.g . . . make before break action . . . versus . . . non shorting type of switch . . .that is no real problem .
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:If using a non shorting type, you will merely have a quick "pop" during band transition on the radio . . . . IF being running while doing the band switching.
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:73's de Edd
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:Might try an old computer data switch box. The rotary switch can be just A & B or some have A-B-C-D .. The switch has multiple contact points, but can be wired to fit your needs.
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Seems i couldn't see past the mechanical configuration of this switch to just break it down to two simple SPDT switches. Just ordered a DPDT new rotary switch.
Thanks
Mitch

12/24/2010 12:36:19 AMThomas Dermody

I think that the Radio Shack switch you have will work. Since there are no great voltage differences from one pole to another on the various sections of the switch, there is no danger of shorting due to a make before break situation, and since your original switch was designed that way, anyway, obviously there will be no problem.

As Edd said, a break before make switch will work just fine in this application. Actually, this kind of switch will work just fine in almost all radios. Temporary voltage spikes and changes are of no concern for most radios (that is, unloading and loading the B supply, when this is done by the rotary switch). There are rare exceptions to this, I'm sure, but it's not typical. Very early radios where the speaker field is across the B supply will suffer damage (sometimes) if the speaker field is removed from the circuit while the radio is in operation. However, I don't know of any radios in which the speaker field is switched, so this is an unlikely situation unless one physically disconnects the speaker.

Anyway, if that Radio Shack switch has three sections and two positions (or more), then use it. It will work well.