walter woods pilot light.

[EDWARDEFFECT1]

i have 166.3 vollts dc on one terminal of the light and -163 dc on the other. the light is 125volt ac.any ideas. i must have something leaking dc into it. there are no identifiers for dirrection with the caps.i have replaced all the large capacitors and the bridge rectifier with a 1000volt 25 amp part. the amp works fine,but no pilot light.i have another post with pictures of the circuit board if it helps....thank any help apreciated......ed

[DJPhil]

i have 166.3 vollts dc on one terminal of the light and -163 dc on the other. the light is 125volt ac.any ideas. i must have something leaking dc into it. there are no identifiers for dirrection with the caps.i have replaced all the large capacitors and the bridge rectifier with a 100volt 25 amp part. the amp works fine,but no pilot light.i have another post with pictures of the circuit board if it helps....thank any help apreciated......ed

That's about right, actually, with one exception. Assuming you didn't have a typo, you should definitely use a higher voltage rated bridge rectifier!
Pure sine AC will rectify to a higher DC voltage than it's original AC RMS value.
To figure the value, multiply the AC by the square root of two = 125VAC x 1.414 = 176.75VDC
There's usually a bit of voltage drop caused by losses in the rectifier and filter caps. Ten volts is about right, especially considering that you might be overloading your rectifier.
I'd strongly recommend at least a 400V bridge, as they're usually not much more expensive at 25A than a 100V version. Mains wiring is full of high voltage spikes of several hundred volts, and depending on your location they can occur from several times a day to a few times a month. It's not uncommon to see short transients of several thousand volts a few times a month where I live!

Regarding the pilot light, I'm not sure what you mean. If it's just a power indicator it might be burned out. It happens a lot with direct mains powered neon lamps, and they're fairly cheap to replace if you don't need to find the exact right shape and size to fit into something, like a particular switch. The only other thing I could think of was the heaters on a tube amp, but then it would hardly be working well!

Hope that helps.

[Enzo]

A neon pilot light rinning on 120VAC sees a voltage that swings up to about 170v, then down through zero and up to 170v on the other polarity.  There are two electrodes in the neon bulb, only one actually glows - I don't remember if it is the positive or the negative.   On AC current, the two electrodes take turns at each polarity, so it appears both are glowing, but they really are taking turns 60 times a second.

Nothing says you can't run it on DC and settle for the same electrode doing all the glowing.


A glowing neon bulb is more or less a short across the voltage source, so they put a resistor in series to limit current, not unlike LEDs in that sense.  Those molded plastic ones have a resistor inside them, so you can connect them right to the 120VAC.


One thing concerns me here.  You say you have 167vDC on each end of this light.  VOltage reading taken with respect to WHAT?   If you measure voltage from end to end onthis light and get +167v, then swap your leads, you will get -167v.   The bulb can act kinda like a rectifier.  I wonder if it is fooling your meter?  But frankly I'd just try a new neon light.

[EDWARDEFFECT1]

hi! thanks for the reply's. dr phil there was a typo. i corrected it.the rectifier i put in is 1000v at 25 amps.the amp works perfectly.just having problems with the pilot light.i already put a new light in and it still doesn't work.the pilot light is an exact replacement for what was in the amp. it is a 2150a1 idi 125vac 1/2 watt.enzo as for the test points i am testing from the chassis ground to each of the leads on the pilot light.i am wondering if the high dc voltage blew out the new pilot light.the ac power comes in on a switch the goes thru a 1k heat sinked resistor. then it goes to the center terminal of a triac. mac15a6. from there not sure what happening with it. i get 124v ac on both sides of the heat sink resistor.thought that was strange and the triac reads 124v ac on all 3 legs.the leads from the pilot light go as follows: i don't have a schematic so bear with me.the lead farthest from the switch (120v/240v switch)goes to one side of a resistor. to the - leg af a 330uf 200v electrolytic.then goes to the minus leg of the 4pin 1000v 25 amp bridge rectifier.the other wire of the pilot goes to a reisistor that t's off into 2 more resistors with the top resistor going to the + leg of another 330uf 200v electrolytic.then it ends on the + side of the bridge rectifier.another words both pilot light lead circuits terminate on the outside legs of the 4pin bridge rectifier.i tested the resistors and the all seem ok.this amp is a hair puller for a rookie.i also tested for ac on both wires of the pilot light and got no ac reading.it just reads dc voltage ...thanks phil and enzo for helping me with this. i'm close,but not there yet on fixing this moose.....ed

[EDWARDEFFECT1]

anymore help appreciated! any more ideas...thanks...ed

[EDWARDEFFECT1]

i got the light working.i was getting a bad  reading on the resistor in circuit. i removed them with my tennma desoldering station.and found an open resistor, the top one of the 3 resistor in a t shape. it was the closest one to the + side of the bridge rectifier.it works now.the light has a slight christmas tree light flashing if you look at it close.must be what you were talking about enzo....thanks for your help phil and enzo....you guys are awesome....ed!!