OT impedance switch question

[deci belle]

'470 @ 5 Watts is big enough'
Sorry, I saw 'Showman' and thought '4 tube amp'.

Ok! I see, Pete— that makes sense too!

Or you could use a conventional DPDT switch and wire the respective poles in parallel (in order to provide more insurance against switch contact failure)

Ya, that's what I did when I made a switch between a SS and Tube rectifier, tubeswell!

[imaradiostar]

Using your data Juan, I did find a very cool SP3T 1/4-40 (7.4mm) bushing switch at Mouser M2024LL1W01-RO NKK Switches | Mouser that has a locking lever and uses a double-pole base. It's rated at 125/250v @6A.

Please read the datasheet for that switch very carefully! It is the correct switch for series/parallel single coil humbucker wiring but it is not the correct switch for single pole 3 throw speaker wiring.

I believe the inexpensive 5 amp lorlin and c&k switches from mouser are fine for impedance selectors. I've used them in very high power circuits with no failures. As suggested above you can always double or triple the connections for increased reliability.

Jamie

[J M Fahey]

Dear imaradiostar/jamie:
at first I thought exactly the same as you, because it LOOKS like a a miniature DPDT "guitar" switch ... but it is not.
Read the datasheet http://www.nkkswitches.com/pdf/MtogglesBushing.pdf and decode it with the code M2024LL1W01-RO
which is correct for a SP3T ON-ON-ON selector.
By the way, it's rated to interrupt 6A, meaning it can safely pass quite higher audio current.
Leg wiring is not intuitive, so attention must be paid to the datasheet, and then checked with a multimeter before actually fixing it in the chassis.
It's a cool switch and I'd love to have it available in Argentina.
Only mod I'd do, is to cut the toggle in half (and filing the end round, of course) so as to make it hard to move, maybe needing a coin or a ballpoint pen cap.

[Steve Conner]

The last time I tried cutting down the toggle on a toggle switch, I found to my dismay it was hollow with a spring inside, part of the mechanism. Switch no workee any more.

[J M Fahey]

Ouch!! Happened the same to me, but on "big" switches; not space enough for a spring in the small ones.
To boot, this one has a "flattened" lever, even less space..
Anyway it's something to be considered.

[imaradiostar]

oh, you're right JM! Sorry to mislead!

It is a fairly high rated switch but I think it would be optimistic to expect it to handle any more current than the aforementioned rotary switches.

What about the tiny military style microswitches? Like the ones in old new sensor pedals but quality US versions, Not the russian ones.

I agree with Steve- I've cut down a few and always ended up destroying the switch!

If you're only trying to switch between two impedances you could easily purchase a short or recessed bat type DPDT mini toggle and have current handling in excess with a tiny package with a small bushing. I've seen them on the internet but I don't recall where. I know they're available!

Here's one- cheap too, from Apex Jr:

http://www.apexjr.com/images/DPDTMINI%20SHOTOGGLE.jpg

I've seen them with the bat almost recessed as well.

Jamie

[deci belle]

I studied the spec-sheet on the Mouser switch some more and it said that for DC the switch is rated for 30vdc @ 3 amps. Dang! So maybe I should use the hole for the 16Ω jack like Pete suggested.

Instead of using the hole for a switch, why not use it for a jack socket wired to the 16ohm tap?
Leave the regular speaker and ext speaker sockets in parallel on the 8 ohm tap, but remove the 'shorting to ground' link on the switched contact.

I can use regular rotary switches for scratch-build Tweed chassis because I'll have 2-1/2" to work with on those…

[pdf64]

DC is 'harder' to switch than AC (a DC arc will sustain, whereas an AC arc will tend to self extinguish as it passes through zero), so a switch's Vac rating would normally be a fair bit higher than for Vdc.
If if you dig a bit deeper, you may find out it's fine.
Pete

[deci belle]

Oh, cool!! Thank you for telling me, Pete!!

[J M Fahey]

for DC the switch is rated for 30vdc @ 3 amps. Dang!

So you can hear DC?
WoW !!!!!!
.
.
.
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It's as pdf said, of course.
To which I add: that current *interrupting* rating means switching OFF *while* current is passing.
If contacts open and close with no current through them and *afterwards* current passes, it's no big deal.
Rather than actual current, the *big* contact destroyer is sparks which fly when there's poor contact between them, either while closing or, much worse, when opening.
Which you will never do because you will not switch impedance while playing.

[deci belle]

Which you will never do because you will not switch impedance while playing.

I sure better not!! No I can't hear DC, but I didn't know that until just now!! haha!! Those DC values didn't seem very high, so it made me worry— I just ordered two of the switches from a lady at Mouser just now! Thanks Juan

[deci belle]

I finally hooked up the 125/250v @6A SP3T 1/4-40 (7.4mm) bushing switch with a locking lever. It fit in the Vibrato Switch hole in the back of my Showman running two power tubes and two rectifier tubes.

It uses a double-pole base. The #3 and #5 terminals are tied together (green wire). I hooked up the #2 terminal (common) to the speaker jack (+); 4Ω tap to the #1 terminal, 8Ω tap to the #4 terminal and the 16Ω tap to the #6 terminal of the switch.

It works.



Thank you all for helping me choose the switch!!