replacement resistors for esl57 crossover

[jonk]

Kiwame carbon film resistors are rated at 1200V and come in both 2 and 5 watt ($1 and $2). The 5 watts won't quite fit between that tabs on the transformer but are very close and could fit with just slightly bending the leads. The 2 watt ones would easily fit but i don't know the required wattage. Anyone know the wattage rating of the originals?

[Fabien Lefebvre]

Originally Posted by jonk

Kiwame carbon film resistors are rated at 1200V and come in both 2 and 5 watt ($1 and $2). The 5 watts won't quite fit between that tabs on the transformer but are very close and could fit with just slightly bending the leads. The 2 watt ones would easily fit but i don't know the required wattage. Anyone know the wattage rating of the originals?

Any news on this old topic ?
Quote from OneThingAudio: "Whereas the "wattage" ratings of resistors are not critical, it should be remembered that each resistor should be capable of handling instantaneous peak voltages of at least 3kV".
VR37 series should be fine. They are rated for 1/2W & 2.5kV RMS (3.5kV DC).
But hard to find: listed only on Digi-Key.

[oshifis]

Why would someone replace the original resistors, unless their ceramic case is broken because of mishandling?
But I am thinking of replacing the original 6x 560pF 3kV ceramic capacitors, because I don't like ceramics for audio. Would these SBE capacitors fit the purpose?

[bolserst]

Originally Posted by oshifis

Why would someone replace the original resistors, unless their ceramic case is broken because of mishandling?
But I am thinking of replacing the original 6x 560pF 3kV ceramic capacitors, because I don't like ceramics for audio. Would these SBE capacitors fit the purpose?

Yes. The SBE caps would work great in this application.
Even with a 100W amplifier (30Vrms/8ohm) the voltages would be well within the capability of the SBE capacitors.

[oshifis]

I was unsure because the originals are 3kV and the SBEs are 1.5kV rating for AC. Given the 292:1 turns ratio (found this value by Googling) the primary can be driven by 5V which seems insane... Or is that not the full AC goes to the capacitors? They seem to filter the AC signal going to the stator of the mid and high section; there is no DC polarizing voltage on them.

[bolserst]

Originally Posted by oshifis

I was unsure because the originals are 3kV and the SBEs are 1.5kV rating for AC. Given the 292:1 turns ratio (found this value by Googling) the primary can be driven by 5V which seems insane... Or is that not the full AC goes to the capacitors? They seem to filter the AC signal going to the stator of the mid and high section; there is no DC polarizing voltage on them.

Capacitor voltage ratings
The 3kV rating on the ceramics is a DC voltage rating. The AC rating is an unknown, but would be no more than 1kV. (VDCrating)/(2*sqrt(2))

The 1.5kV rating for the SBEs is an AC rating. The DC rating for the SBEs is 5kV. What is important in this application is the AC rating.


Transformer step-up ratio and applied voltages
The full transformer ratio is about 290:1, but the mid-tweeter section only gets about 90:1.

The two paralleled 650pF caps feeding the tweeter will, worst case, only see half of the total step-up (45:1) at low frequencies since the 270K resistor references to the center tap, not the opposite phase side of the winding.

The 650pF cap feeding the midrange section forms an AC voltage divider with the midrange ESL capacitance, which is 200pF. So, worst case, the 650pF cap will see about 1/4 of the total voltage coming from the 90:1 winding.

[oshifis]

Originally Posted by bolserst

Capacitor voltage ratings
The 3kV rating on the ceramics is a DC voltage rating. The AC rating is an unknown, but would be no more than 1kV. (VDCrating)/(2*sqrt(2))

The 1.5kV rating for the SBEs is an AC rating. The DC rating for the SBEs is 5kV. What is important in this application is the AC rating.


Transformer step-up ratio and applied voltages
The full transformer ratio is about 290:1, but the mid-tweeter section only gets about 90:1.

The two paralleled 650pF caps feeding the tweeter will, worst case, only see half of the total step-up (45:1) at low frequencies since the 270K resistor references to the center tap, not the opposite phase side of the winding.

The 650pF cap feeding the midrange section forms an AC voltage divider with the midrange ESL capacitance, which is 200pF. So, worst case, the 650pF cap will see about 1/4 of the total voltage coming from the 90:1 winding.

Can I use 600V rated capacitors if I don't exceed 10V AC input?