polk monitor 12 series ll recap, help!

danga

Hello, Im new to this forum. I will replace capacitors on my polk monitor 12 series ll with clarity px.
the resistor reads: 2 ohm 5% cw5, Im assuming cw5 stands for 5 Watts, what is a good replacement for it?
also, what is the small brown thing on top of the 4.2 uF capacitor and what to replace it with?

Thanks in advance guys.

Nightfall

I believe the brown thing is a polyswitch.

pitdogg2

Correct poly switch coupled with the cap from what I can tell. You well need to replace that cap also, many here omit the poly switch when we recap and replace it with a .5 ohm resistor but beware you will no longer have that safety factor with your tweeter. You will need to be more careful with the volume knob.

OK I am not sure if you should also bypass that cap with a 1/2 ohm 12 watt resistor buy if it is that way with the poly I'm going to lean towards yes you should.

Upon further inspection of your pictures yes it is get a 4.2 uf poly cap and bypass with 1/2 ohm mills 12 watt resistor. Unless someone with deeper knowledge disagrees and has a better idea. Just upping the cap value I believe will mess up xo point ....you could also just omit the resistor but that may make the tweeter too hot.

westmassguy

Not so fast. The Polyswitch was added in the revised drawing. It operates somewhat differently than on previous Monitors.

pitdogg2

Maybe because they went from sl2000 to sl2500. Still it is for tweeter protection ...right? Two different caps in that network the other bypassed with 2ohm resistor. Sorry Dave I didn't look at the first incarnation. Working from a tracfone can be laboring at times.

westmassguy

pitdogg2 wrote: »

Maybe because they went from sl2000 to sl2500. Still it is for tweeter protection ...right? Two different caps in that network the other bypassed with 2ohm resistor. Sorry Dave I didn't look at the first incarnation. Working from a tracfone can be laboring at times.

pit, if there's and earlier version of the Monitor 12 with the SL2000, we don't have schematics for it. Both schematics we do have, show an SL2500.
In previous Monitors, the fuse or Polyswitch is located before the hi-pass circuit. When the fuse blows or the Polyswitch is tripped, the hi-pass circuit is disconnected, saving the tweeter (hopefully).
In the revised schematic, the Polyswitch is smack dab in the middle of the circuit.
It's after the contour network (12uf cap + 2 ohm resistor), but before the other 12uf cap and bypass shunt. The Polyswitch is in parallel with a 4.2uf cap. If the Polyswitch trips, all the current now flows through the 4.2uf cap, which is in series with the 12uf cap that follows it. A quick calculation shows the total capacitance for the two caps to be about 3.1uf. This raises the crossover point dramatically. In theory (I'm guessing here), the lower frequencies (upper midrange and lower treble) the tweeter normally handles are reduced or eliminated, thereby protecting the tweeter from excessive voice coil movement.

pitdogg2

So when its tripped we still have a tweeter?

westmassguy

Theoretically, yes, but only the highest frequencies

pitdogg2

So I'm dumbfounded as to why it was added as we all know that once tripped it is going to trip easier and more often...seems to me that they should of had a redesign to better protect if that was the reason it was revisited.
Thanks Dave still learning here... you da man

westmassguy

No worries, I'm not sure either why they took a step back like that.

littlewoodboats

Could the polyswitch have been put in place like this to protect the capacitor?

westmassguy

littlewoodboats wrote: »

Could the polyswitch have been put in place like this to protect the capacitor?

Caps don't normally need protection.