Spark Killer Capacitor

Thread Starter

beginnersluke

Joined Aug 26, 2015
35
Hello,

I am researching/preparing to replace the capacitors on a power supply board in a 1970s reel to reel machine (a TEAC A-6300).

I have dug up (okay google dug up) the service manual which has a handy parts list and PCB layout. Yay!

However, one thing on the parts list has me confused. After listing some standard capacitors, a la:

C1, C2, C4 -- Elec -- 330uF --- 50V

We get to:

CR701-703 -- Spark Killer -- 0.1uF + 120Ohm 400V

The way this is drawn on the layout (a view of the PCB with tracers, then schematic symbols showing where the components go), this is one single component. (Not a combination of two components.)

When I look at capacitors on Mouser, there's no "spark killer" category alongside the film, electrolytic, and ceramic capacitors. What would I need to look for?

While I'm at it, I also don't see a metalized Mylar category on Mouser. What is a suitable replacement for this part? (This is another 0.1uF 400V capacitor -- or 9, actually).

Thanks in advance for the help.

(You can probably find the service manual through google, as I did, if that helps. It's a TEAC A-6300 as mentioned. It appears on manual pages 47 and 48,)
 

drc_567

Joined Dec 29, 2008
1,156
Is this part in parallel with some kind of inductance? If that is the case, then it, or they, are reverse biased diodes. The purpose is to dampen out a coil current caused by an abrupt open circuit ... a switch opening.
 

BR-549

Joined Sep 22, 2013
4,928
If you are sure that there is not a 120 ohm resistor on the board, you have all the info you need to build your spark killer.

Remove one and measure the resistance.
 

Thread Starter

beginnersluke

Joined Aug 26, 2015
35
Thanks for the replies. I searched for Snubber on mouser and this seems very close to what I would need:

http://www.mouser.com/ProductDetail...=sGAEpiMZZMv1cc3ydrPrF9O2k7r3G2yZK70uhKwlT0Y=

Is this correct?

There is a 150ohm and 100ohm variant. I'm trying to understand the formulas, but which would be better for my purposes (or is this critical enough that I should add a resistor in parallel to the 150ohm to get 120ohms)?

What about the metalized mylar capacitor? Is there a modern equivalent?

Thanks so much for the help.
 

Kjeldgaard

Joined Apr 7, 2016
476
It is a combined series connection of resistor and capacitor, sometimes made so that the resistance is virtually part of the metal foil of the capacitor
It used to be incredibly rugged components when, as they are made specifically for snubber use.
So if the RC component looks good physically, so I doubt that there's anything wrong with it.
But if it must be changed, then it is usually not the great importance if the resistance is 100, 120 or 150 Ohm.
 

EM Fields

Joined Jun 8, 2016
583
If you are sure that there is not a 120 ohm resistor on the board, you have all the info you need to build your spark killer.

Remove one and measure the resistance.
That can't be done conventionally since the snubber is a two terminal device and the RC junction is internal.
However, it can be done by resonating the snubber's capacitance with an external known inductance, measuring the current through the series resonant circuit, and subtracting the inductor's resistance from the total resistance.
 

Thread Starter

beginnersluke

Joined Aug 26, 2015
35
I'm going to try to remove the circuit board and get a better look (for now, I was just going off the service manual).

I actually realized I was looking at a similar model in the manual, and the one I'm working on has 23 (!) of these, which given the price on Mouser means that's not a solution for this.

That can't be done conventionally since the snubber is a two terminal device and the RC junction is internal.
Do you mean that I couldn't just connect a capacitor and resistor in series to accomplish the same job?

Thanks,

Luke
 

#12

Joined Nov 30, 2010
18,224
Do you mean that I couldn't just connect a capacitor and resistor in series to accomplish the same job?
No, he means you can't take a snubber apart and measure the two components because they are manufactured as one capacitor with some resistance in it. Any metal film capacitor will do the job, Polypropolene, polystyrene, pollywannacrackerene...whatever. But they are bulky. I would consider a 0.1 ceramic/400v and a 120 ohm resistor, but I wouldn't touch this job. I have a 1975 guitar amplifier in for work right now and all the metal film capacitors are as good as new. No measurable leakage with 400VDC applied. What makes you think 23 snubbers need replacing?
 

Thread Starter

beginnersluke

Joined Aug 26, 2015
35
What makes you think 23 snubbers need replacing?
In some sense that's part of what I'm trying to figure out -- the question of 'do they need to be replaced'?

When I started this thread, I wasn't even really sure what they were when I saw "spark killer" as a capacitor type on the parts list. It would be great if they could be left alone. I've recapped a few power supplies, but those were full of electrolytic capacitors (with maybe 1 or 2 film in there).

This one surprised me. It's got 6 electrolytics, 1 Metalized mylar, then 23 of these snubber/spark killers.

Is it fair to say that when people speak of replacing capacitors, they're speaking of the electrolytic caps (unless others present a reason to be replaced)? Sorry, I'm still learning (which is why it's great to have a resource like this).

Thanks!

Luke
 
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