Need a guru with switching

[AZJimC]

Ive got a large resistor that totals about 5kohm with a tap at about 2Kohm  its likely about 35-40w. I have it wired for sag on whole system. I want to use a On-Off-On toggle to get three positions, and I have no problem making it a Hi-Lo-Med, but I'd rather have Lo-Med-Hi. I know there's a way to do this with the DPDT switch, but I've been racking my brain and have locked up on the logic. HELP!

[HotBluePlates]

... I want to use a On-Off-On toggle ... I have no problem making it a Hi-Lo-Med, but I'd rather have Lo-Med-Hi. ...

You're using the wrong switch. If you want a progressive order (Lo-Med-Hi), you need a DPDT On-On-On switch.

A DPDT On-On switch flips between Circuit A and Circuit B for both poles at the same time. A DPDT On-Off-On switch selects Circuit A, then No Connection, then Circuit B for both poles at the same time. A DPDT On-On-On switch selects Circuit A for both, then Circuit A for one and Circuit B for the other, then Circuit B for both.

See drawing below, and realize that the middle position of the switch has one pole at one circuit while the other pole is at the other circuit. This feature, plus a piece of wire to properly connect the two poles, is what gives the progressive action of the switch.

[clyde]

A few weeks ago I was looking for something similar for 3-position gain adjustment.  PRR posted a switch.  Is this the same one?  Also, is it available in mini-toggle format?  Thanks.

[plexi50]

I wouldnt use a mini toggle switch for the B+ in an amplifier if i read your post right. You need a heavy duty DPDT switch

[clyde]

Signal, not B+.

[AZJimC]

You're right HBP, and I wish I had one of those, but I only have a on-off-on. in searching the web I found something for a dual resistor circuit intended for something else that used an on-off-on to switch in resistance for a hi-med-lo.

Now I cant even find that circuit to remind me how they did it. I know it required both poles, and placed a resistor between the two off lugs I think. I'd order an on-on-on switch, but I'm trying to get this amp ready to go on a trip to Oklahoma, leaving Tue. I'm in a little bitty town between Kingman, AZ and Las Vegas, NV. It would be iffy I could even get one here for any price before I leave, even if I waited till Wed.

I do have one of the rotary that Doug sells for impedance switching, and hookup on that would be straightforward, but I was hoping I could use the toggle since I'd have less modification to make it fit.

[AZJimC]

Re: How to wire a SPDT On-Off-On switch

R1 = 10K, R2 = 4.7K, R3 = 4.7K

I found this, finally, but I'm not sure how to translate it to my usage. It uses a SPDT for some bicycle thing. It uses three resistors, but does achieve a Lo-Med-Hi.

[HotBluePlates]

A few weeks ago I was looking for something similar for 3-position gain adjustment.  PRR posted a switch.  Is this the same one? 

Dunno, didn't see the thread.

Also, is it available in mini-toggle format?

Mini-toggle is how I've used it before. Got mine from Mouser, but there was a lot of looking through catalogs and data sheets to figure out the right switch to use.

[HotBluePlates]

I found this, finally, but I'm not sure how to translate it to my usage.

It doesn't, because the Hi-Med-Low refer to output voltage levels from a voltage divider, and the switch is used to short out resistor sections. Your usage needs high-med-low series resistance to create differing sag levels.

To make this scheme work for you, you'd need 3 series resistances. With the 2-section resistor you have now, the Med & Low settings would be the same.

You're right HBP, and I wish I had one of those, but I only have a on-off-on.

I've tried to figure a way to make an On-Off-On and 2 resistors (or a tapped resistor) work, but it doesn't.

I'm sorry to say that it's either get the right part or settle for the present result. I think Hoffman sells the progressive Carling switch.

[clyde]

http://www.el34world.com/Forum/index.php?topic=16310.0

[HotBluePlates]

A few weeks ago I was looking for something similar for 3-position gain adjustment.  PRR posted a switch.  Is this the same one? 

http://www.el34world.com/Forum/index.php?topic=16310.0

I see... He linked a thread where someone else linked to the switch.

The switch I posted is different from the one in the link because it is a mini-toggle (like you asked for) instead of a big power switch. That said, it does the same function in the same way.

The data sheet link at the Mouser page will show you this, if you scan it for the switching arrangement of the 7211.

[clyde]

Many thanks HBP.

[PRR]

I do not like this:

[eleventeen]

I was trying to come up with a way to do this using a couple of diodes to block current...but I was unable to come up with a scheme. Maybe someone else can figure something out.