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SUPPORT FORUMS FOR ZKITS >> ZKIT 1 Support forum >> 100 ohm resistors on input transformer?
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Message started by GDSellman on 08/04/13 at 20:40:46

Title: 100 ohm resistors on input transformer?
Post by GDSellman on 08/04/13 at 20:40:46

I am trying to finish up my first ZKIT1 build and looking at the PCB there are spots for two 100 ohm resistors to ground on the wires coming from the input transformer to the heater wires. Do I populate both? One? None? I don't see the parts listed in the Bill Of Material, so any help is appreciated.

Title: Re: 100 ohm resistors on input transformer?
Post by dank on 08/04/13 at 23:05:53

This is a late mod for hum. You can leave unpopulated for now and add them later if your hum is too loud. My Zkit1 doesn't have them and my hum is fine. I don't know what the wattage should be, how much room is allowed for them on the PCB? 6.3 vac and 100 ohms says 0.4 watts, meaning that it better be about a 2w resistor or more or its going to get HOT. You can populate one or both...I'd decide by what it does to the hum level.

Dan

Title: Re: 100 ohm resistors on input transformer?
Post by mboxler on 08/05/13 at 04:11:49

Here's Steve's notice of the upgraded PCB.

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1343961059

Here is a link to an explanation of the "artificial centre tap".

http://www.valvewizard.co.uk/heater.html

If the Edcor's heater outputs were center tapped, the center tap wire would go to ground. But since it is not center tapped, the TWO 100 ohm 1/2 watt resistors act as a center tap to ground.

I happen to have two extras that I'd be glad to mail to you. It's a bummer that the BOM hasn't been upgraded to include the two resistors. PM me your address if you want them.

Mike