epoxy coated resistor question

digthisbigcrux · April 07, 2011, 07:30:47 PM

i need to order a couple of these and im not sure really what to get. they are lime green and about the size of a 1/4 watt resistor. using the electronics assistant application i deduced the value to be 2.2 millihenries. how do i figure out the power rating? are the ones i see on mouser that are tan colored the same thing? i read on another forum while researching these that you could just replace them with resistors, is that the case? they are in the power section of a 5150 if you are curious.

danielzink · April 07, 2011, 09:27:47 PM

Quote from: digthisbigcrux on April 07, 2011, 07:30:47 PM
i need to order a couple of these and im not sure really what to get. they are lime green and about the size of a 1/4 watt resistor. using the electronics assistant application i deduced the value to be 2.2 millihenries. how do i figure out the power rating? are the ones i see on mouser that are tan colored the same thing? i read on another forum while researching these that you could just replace them with resistors, is that the case? they are in the power section of a 5150 if you are curious.

They're more than likely capacitors.

I'll try and dig up a couple pics for reference for you.

Dan

danielzink · April 07, 2011, 09:34:28 PM

http://www.robotroom.com/Big-Trak-2.html

the third paragraph marked "Capacitors" shows one of his pink "resistor looking" capacitors.

This is one of few references I can find to this type of cap.

Unless you're talking about axial tantalum caps....but they're more of a "mustard" color....

Dan

davent · April 07, 2011, 09:47:45 PM

These greenies were pulled out a baby monitor and i believe are some sort of inductor. Are they what you're looking for?

dave

danielzink · April 07, 2011, 09:51:27 PM

Ooooooo !

Cool davent ! I learned something new today!

Dan

digthisbigcrux · April 07, 2011, 09:51:45 PM

here is what im looking at:

danielzink · April 07, 2011, 10:08:23 PM

Hmmmmmm........

My vote is still capacitor.....

digthisbigcrux · April 07, 2011, 10:38:05 PM

side note. i measured it with my multimeter for resistance. even at the highest setting on my meter (20meg) i got open circuit. this is why i drew the conclusion that they needed replaced. there are a couple of other ones on the pre amp board that show in the ball park of 2 meg when measured.

davent · April 07, 2011, 10:47:21 PM

Are you disconnecting one end of the component from the circuit to do the measurement? If it's in circuit, readings can totally skewed.

dave

digthisbigcrux · April 07, 2011, 10:48:45 PM

it was completely removed from the circuit. and i also measured it in circuit with the same results.

LucifersTrip · April 08, 2011, 12:26:14 AM

Quote from: digthisbigcrux on April 07, 2011, 07:30:47 PM
electronics assistant application i deduced the value to be 2.2 millihenries.

mH & uH (microhenries) are measurements used for inductors:
http://www.taydaelectronics.com/servlet/the-Inductors/Categories

~arph · April 08, 2011, 04:30:07 AM

Quote from: digthisbigcrux on April 07, 2011, 10:38:05 PM
side note. i measured it with my multimeter for resistance. even at the highest setting on my meter (20meg) i got open circuit. this is why i drew the conclusion that they needed replaced. there are a couple of other ones on the pre amp board that show in the ball park of 2 meg when measured.

It has been hinted before, It could be a capacitor. Does it pass AC ?

egasimus · April 08, 2011, 04:56:05 AM

Looks like a 1% resistor to me.

defaced · April 08, 2011, 09:52:28 AM

100pf cap, C201 and 202: http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/newamps/peavey_evh5150.pdf

~arph · April 08, 2011, 10:10:19 AM

Then why is it connected to that diode?

defaced · April 08, 2011, 10:35:01 AM

Those are flyback diodes that go across the OT primary to ground so if the OT loses loading on secondary, they may save the OT from flyback voltage spikes. Look at the right of the schematic near the OT, CR200 and CR 201. Both the caps and the diodes are connected to ground.

~arph · April 08, 2011, 10:42:07 AM

Sorry, my bad, I saw them but thought they were not connected.. but thay are.

defaced · April 08, 2011, 11:07:23 AM

It's cool. That schem is a marginally ok scan to begin with. I had to zoom in to verify they were grounded too.

So, these 100p caps, they are placed at the grids of the power tubes to help with oscillation/stability by forming a low pass filter with the grid resistors and shunting high frequencies to ground. They will not keep the amp from running, in fact, most amps don't have these caps. But if there is an oscillation problem, they will help the power amp stay stable.

So the question is, why do you need to replace them? Did a failed power tube take them out? If so, 250-500v ceramic caps will do the job nicely. This part of the amp should only see ~60v P-P AC voltages.

Peavey's tech department is very free with info. You could call them and get exact replacement info from them and probably order the part from them too.

digthisbigcrux · April 08, 2011, 08:37:10 PM

thanks for the info. yeah bad tubes took them out as well as one of the 10 watters. the amp works but hums and crackles. i was checking values on the board and didnt think anything should be completely open circuited at 20 megs. it was just a matter of figuring out what they were.

and i meant to put inductors, not resistors in the title. it was very late haha.

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epoxy coated resistor question