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Snubber Cap

David_NC

David_NC

Super Member
Over the weekend, we were enjoying some music in the back yard. I was using my recently restored Pioneer ER-420 tube receiver. As we were winding down, I heard a small pop, and the GFCI tripped. It would trip whenever I plugged in the receiver - on or off - and had it connected to a cheap USB DAC connected to a PC. My multimeter showed full line voltage between the RCA jacks on the DAC and the receiver's chassis.
Opening it up didn't show anything, but clues indicated it was the transformer or switch / wiring. In this model, the power switch is enclosed in a heavy steel 'box' that's accessed by removing the front panel. Thinking that the switch or wiring had perhaps shorted, I started there. Here's what I found:

IMG_0614.JPG IMG_0615.JPG

Besides being hidden from view, this cap wasn't really documented in the manual. Still, this serves as a warning to those with 50+ year old PIO caps. It was rated at 400 volts, but 120 was too much for it, these days. So, I need to install a new snubber. It doesn't have to be 400 volts; that cap is similar to the dozens of caps that were replaced, so I'm assuming they used a part on hand vs a specific cap for this purpose.
How would these work for this purpose:
https://www.amazon.com/dp/B07QXZLXV...colid=X6KL6NN4353O&psc=1&ref_=lv_ov_lig_dp_it
51secVgFWkL._AC_SL1100_.jpg

.047uF is fine for the original .05uF, and all that I see are rated at 275 V, and I'd think that'd be fine, too. I've read that a resistor should be installed in series; if so, what type and value should I use? Thanks for any advice or ideas on this.
Here's the receiver in question, if anybody was curious:
ER-420 -1.jpeg
 
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Those caps will work fine. You'll notice that a 400V cap was used for 117V AC service. There is a bit more to it than that. When you shut the receiver off, the magnetic field in the power transformer collapses. This causes it to generate a high voltage spike; the cap prevents that spike from arcing across the switch. It also helps out the switch contacts when turning the unit on, since as you discovered, the switch arcs as it starts to make contact. I guarantee that switch is rare; you might want to give it additional protection by placing a current inrush limiter in series with it. And I would replace the filter capacitors in the power supplies if this has not already been done. That will give your power transformer a chance at a longer life.
 
atmasphere said:
Those caps will work fine. You'll notice that a 400V cap was used for 117V AC service. There is a bit more to it than that. When you shut the receiver off, the magnetic field in the power transformer collapses. This causes it to generate a high voltage spike; the cap prevents that spike from arcing across the switch. It also helps out the switch contacts when turning the unit on, since as you discovered, the switch arcs as it starts to make contact. I guarantee that switch is rare; you might want to give it additional protection by placing a current inrush limiter in series with it. And I would replace the filter capacitors in the power supplies if this has not already been done. That will give your power transformer a chance at a longer life.
Click to expand...

Thanks for the info. So no resistor is needed with this cap? All other vulnerable caps have been replaced, and I use a power strip for equipment like this with old and hard to find power switches.
 
Too low a voltage. Frank uses 1000 volt, because inrush current at turn on is very high. That is why the originals (if they were originals) failed.
 
WaynerN said:
Too low a voltage. Frank uses 1000 volt, because inrush current at turn on is very high. That is why the originals (if they were originals) failed.
Click to expand...
Now I'm confused! I don't see snubber caps rated that high; do you know what he uses for this? This was a 54 year old Suzuki and was definitely original, based on how and where it was installed and that it's identical to the caps that were originally elsewhere on this receiver. Thanks.

tonesteroc said:
The infamous "suzuki bomb" strikes again.
Click to expand...
And I was hoping the Suzukis would simply make it go fast... I guess they did, in terms of putting the receiver out of service again! :rflmao:
 
If they're anymore Suzuki bombs, change them all. do a search, my teac A4010S had them, they don't open, they short and blow up. good luck btw.
 
Actually,there are two different models of caps for this type of usage, depending on their circuit position;

X2,which is intended for use across the power line.
Y2,which is intended for use between the phase or neutral line and a chassis.

Most X2 & Y2 capacitors are rated in the 275-300 VAC range. These are designed for use in 120 & 240 VAC applications.

Unless specifically rated for X2 or Y2 use,I strongly advise against using any other type of capacitor for this type of service,regardless of what their DC voltage rating may be.
 
tonesteroc said:
If they're anymore Suzuki bombs, change them all. do a search, my teac A4010S had them, they don't open, they short and blow up. good luck btw.
Click to expand...
Yep, they were all changed.
arts said:
Actually,there are two different models of caps for this type of usage, depending on their circuit position;

X2,which is intended for use across the power line.
Y2,which is intended for use between the phase or neutral line and a chassis.

Most X2 & Y2 capacitors are rated in the 275-300 VAC range. These are designed for use in 120 & 240 VAC applications.

Unless specifically rated for X2 or Y2 use,I strongly advise against using any other type of capacitor for this type of service,regardless of what their DC voltage rating may be.
Click to expand...
How about as a snubber, as in across the terminals of the switch? I'd think X2, as it's across the powerline when the switch is open.
 
David_NC said:
Now I'm confused! I don't see snubber caps rated that high; do you know what he uses for this? This was a 54 year old Suzuki and was definitely original, based on how and where it was installed and that it's identical to the caps that were originally elsewhere on this receiver. Thanks.


And I was hoping the Suzukis would simply make it go fast... I guess they did, in terms of putting the receiver out of service again! :rflmao:
Click to expand...

They are ceramic caps used on switches and things like that to take out on/off noises that could end upstream. I think they are .01uf.
 
Pop went the weasel! Be sure that the replacement cap is specified for service connected across the AC mains. Such caps meet safety approvals for fire hazard. Nor all caps with adequate voltage rating have this approval.
 
David: No worries, as Arts has already explained, a 275 V(AC) rating is perfectly normal for modern day X/Y type safety caps. The actual test voltages for these are quite a bit higher - for example, an X2 with less than 1 µF cap, that complies to EN60384-14, should withstand pulse voltage of up to 2.5 kV. And the same standard also includes an endurance test with 1 1/4 or respectively 1 3/4 times the rated voltage for X or respectively Y types at elevated temperature for 1000 hours, including one 0.1 second 1 kV burst every hour.

That you find higher voltage ratings in older equipment typically has two reasons: For one thing, those caps weren't specific X/Y types yet - so the circuit designers rather used regular types, that were suitable for the job. And then the rating might also merely refer to V(DC) rather than V(AC).

And yes, as Tom wrote, an additional 100 Ohm resistor in series typically isn't a bad idea.

Greetings from Munich!

Manfred / lini
 
If in doubt, to protect a power switch contact, simply install a 1000V 0.01uf disk cap across the contacts and move on to bigger fish...
 
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