Illuminated power switch?

[STURMJ]

I am using a Illuminated power switch (I hope).  I assume the power for the LED would best come from the filament-heater supply.  Would it be best to wire it after the last tube connection (daisy chained ), or as separate wires coming directly from the power supply?  Also, should I add a capacitor near the switch to keep noise down?
thanks!

 

[Paul Birkeland]

The answer(s) to this question could depend a lot on your switch.

If it's a 12V DC light, you could get that from the raw filament DC supply.

If it's any other voltage than 12, let us know and we can provide better direction.

Also, if the switch does end up fitting the cutout, do post the part number, as substitutes are a bit uncommon.

-PB

 

[Grainger49]

Stay away from any neon illumination.  It is an arc. 

 

[STURMJ]

It is a round switch.  I superglued a piece of aluminum under the sock switch hole, drilled a starter hole in the center of the rectangle hole (in the glued piece), then used a stepped drill bit to open up the circle.  then removed the glued piece.  It is 22mm which perfectly consumes the rectangular hole.
On the data sheet it recommends a ~400 ohm resistor at 12V and ~25ohm for 5V.  My concern is introduced noise.  My guess is that the best option is to take it from the origin of the heater voltage on one or both of the heater supplies (but I might be wrong  ).

 

[Grainger49]

You are right.  This sounds like an LED so if you are worried about noise put a 220uF low ESR electrolytic across the LED.  Observe polarity.

And post a picture after you are through.

 

[Paul Birkeland]

I would be pretty surprised if an LED introduced noise that was more significant than the ripple on that supply and the noise from the LT1085, I'd just leave it disconnected until the preamp is working, then put it in on one of the 12V rails.

 

[STURMJ]

cool; thanks

 

[STURMJ]

Ok, I got it done and it sounds great.  Then I connected the power to the led ( assuming it is led). I took positive from terminal 31 and went to the nearest gorund for neg,  There is a 100uf electrolytic and a small value film cap there too between the pos and neg posts, and a 1k resistor on the pos post ( per the data sheet).  That caused bad buzzing in one channel and went away when I cut the pos off the switch (led).
So I plan to try larger value caps unless you guys think its not worth the effort at this point.  I'll be happy with no little blue dot if the buzzing can't be gotten rid of.
what do you think?

 

[Paul Birkeland]

Did the diode actually light up?

Did you install the 400 Ohm dropping resistor?

 

[STURMJ]

I lit up nicely..I just used a 1k resistor to the pos terminal. The data sheet recommended something like 950ohm for 12v. I had some 1k around and figured that should be good for the 13 volts. was I wrong?

 

[Paul Birkeland]

Everything that you're doing sounds correct, what I would do is this:

31/28 are the +/- of that unregulated ~12V supply.  Take a shielded twisted pair of wires and solder them to these terminals.

Run the pair up to your switch, then solder the 1K resistor directly to the switch, then the wire from 31 to that resistor, and the wire from 28 to the ground of the switch light. 

If there is still noise after this, post a link to the switch and we can suggest other possibilities.

-PB

 

[STURMJ]

That may be where I went wrong. I have the neg terminal grounded. Ill try again and report back.

 

[Paul Birkeland]

Grounded to where?

 

[STURMJ]

Just to ome of the chasis grounds, the one near the volume and balance pots.

 

[Paul Birkeland]

If you use any old chassis ground, you will draw DC current through the chassis

 

[STURMJ]

yep...that did it.  I left the caps in place since they were already there. Works loke a charm now that I did it right ;D

 

[Paul Birkeland]

It's hard to overstate the value of learning in this manner, way to go!