Quad ESL57 EHT resistors

[NatJS]

I'm rebuilding the EHT power supplies in my ESL57s. Do the 330k and 2.2M resistors need to be high voltage parts or will standard resistors do? How about the resistors in the audio transformer box?

Also, one of the dust covers has a tiny, tiny pin prick hole in it - I've read that the solution is to put a small piece of tape over these defects, but also not to use sellotape - but then, what tape should I use?

Thanks

Nat

 

[jan.didden]

That depends very much on where the resistors are in the circuit. If they are on the primary side of the transformer, most probably not.

Is there a schematic where we can see the resistors?

Jan

 

[candersson]

It was a long time since I rebuilt mine, but if I remember correctly, the secondary side has about 600V across the resistors, but since it is a voltage divider the 330k sees about 1/8 of the voltage. Better be on the safe side and select 1500V resistors.

I did not rebuild the crossover so no idea for each resistor except that the transformer is something like 110:1 and max 17V input which should end up with max 2kV across the network.

 

[NatJS]

Here's a schematic for the power supply and crossover sections. It looks like the two resistors in the power supply are all on the 'low' voltage side (which I think is still 610v), and if I understand it the resistors in the crossover are at a much higher voltage.

Can you recommend where to get high voltage resistors? I've been looking on Mouser, Farnell, RS, Digikey and although Mouser lists them almost none are in stock and are on a very long back order.

 

[rayma]

Caddock MG Resistor Series | Rhopoint Components

 

[stokessd]

The input resistors on the EHT see the output voltage of the transformer which is either 610v or 590v RMS nominal depending on which tap is being used. Voltages are typically a little higher here in the USA. I can't speak to the performance on the other input voltage taps.

I use these for the EHT:

VR37 330K Resistor

VR37 2.2 meg Resistor


These are good to 3500V. So no worries.


The diodes I use are 3000v units, but they appear to be out of stock at the moment:
EHT diodes




For the Input transformer, I step up a series to the VR68. These are good to 10KV

VR68 150K Resistor

VR68 180K Resistor

VR68 270K Resistor




Hope that helps,
Sheldon
quadesl.com

 

[Zung]

For your amusement, this is one of my EHT units, 40+ years of age and still going, complete with the original resistors; the little one sees about 900Vpeak and I seriously doubt it's a HV resistor. Of course, you should use those mentioned above.