Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => AmpTools/Tech Tips => Topic started by: Willabe on May 27, 2011, 03:10:34 pm

Title: What ratings for Rotary switch for sub. box?
Post by: Willabe on May 27, 2011, 03:10:34 pm

It's time I built a few sub. boxes for coupling/bypass caps and grid/cathode/plate resistors.

What are you guys using for switching?

I have a C&K 12 pos. rotary switch rated at;    350mA @ 125 vdc and 2.5A @ 125vac. I also have an Alpha 12 pos. rotary switch that IIRC is rated the same.

Are these safe for this type of use?

I was thinking 2- 12 pos. switches in each box would be plenty.

Also what type of housing should I use? Seems to me it might be best to use a plastic box for safety?

And how about the clip leads? Type/length/ratings?


        Thanks,     Brad       :icon_biggrin:




          

Title: Re: What ratings for Rotary switch for sub. box?
Post by: HotBluePlates on May 31, 2011, 10:37:45 am

The 2.5A switch is overkill, but will work fine. Really, the 350mA switch is overkill as well.

For most applications, you probably won't need to worry about the voltage rating, as your switches seem sufficient. If this were a permanent part of the amp, I'd look harder at switch ratings.

A plastic housing makes sense, if you think you might use the sub box for swapping components near B+ voltage.

Title: Re: What ratings for Rotary switch for sub. box?
Post by: jjasilli on May 31, 2011, 02:19:20 pm

For caps & resistors carrying signal, like coupling caps, running wires to & from components outside the amp will add a lot of noise to the signal.  To minimize noise, a shielded or metal enclosure would be best to house the components.  For leads you can use shielded microphone cable.  The braided shield connects the amp chassis & substitution box to share chassis ground.  The inner leads are your test wire jumpers. 

Title: Re: What ratings for Rotary switch for sub. box?
Post by: Willabe on May 31, 2011, 02:32:52 pm

Quote from: HotBluePlates link=topic=11662.msg 108201#msg 108201 date=1306856265

The 2.5A switch is overkill, but will work fine. Really, the 350mA switch is overkill as well.

It's the same switch, rated in AC and DC.

I thought they would be up to the task, but wanted to make sure.

Thank you both very much for your answers and input.


                   Brad           :icon_biggrin:

Title: Re: What ratings for Rotary switch for sub. box?
Post by: overtone on May 31, 2011, 04:01:10 pm

I use make-before-break rotary switches, it helps prevent the pops between each selection a little.

The home-brew sub-box that I use the most has two 12 way barrier strip terminals on top and a flip top cover. I load this up with different capacitors / combinations to audition various types or values before committing myself.

It also has a another 12 capacitors permanently inside and I can select between a permanent one or any selected one in the barrier strip by flicking a switch. I like this a-b function. Or I just use the permanent ones to quickly run through the standard values to get a feel of things and what options there are.

So that is one 12 way MBB rotary switch plus a change over switch to select between the permanent caps or the exotic ones on test under the flip top.
Best, tony