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SUPPORT FORUMS FOR ZKITS >> ZKIT 1 Support forum >> ZKIT BOARD REVISION
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Message started by Steve Deckert on 08/03/12 at 03:30:59

Title: ZKIT BOARD REVISION
Post by Steve Deckert on 08/03/12 at 03:30:59

As of August 2012 the ZKIT1 board has been revised to reflect the Edcor transformer color codes for the recommended Edcor transformers.



Since the Edcor power transformer does not have a center tap, we have included a place for a pair of 100 ohm 1/2 watt resistors that go between each leg of the 6.3VAC and ground.

If you are using a different transformer, like the original Decware, or a Hammond 272FX, both have center tapped 6.3 volt windings in which case the 100 ohm resistors would have no effect.  NOTE: If you use one of these other transformers with a center tap, be sure it is connected to ground on the circuit board.  The spot marked "Chassis Ground" would be a good spot.  If the board goes into a metal chassis of some sort, then a this spot can also be used to ground the metal chassis to the board.  The earth ground on the IEC connector can then be connected to the metal chassis instead of the circuit board.

Steve


Title: Re: ZKIT BOARD REVISION
Post by mboxler on 08/04/12 at 15:10:03

Hi Steve...

For those of us that have purchased the 9/2011 version of the board, would you recommend adding these resistors as well?  If so, and when you have a moment, could we get a picture of the new board, so we can see where exactly to attach the resistors?

Side note...I accidentally installed the 1K 5W resistor 1/2 inch from PCB instead of the recommended 1 inch.  Should I replace the resistor and install the new one correctly?

Thanks, Mike

Title: Re: ZKIT BOARD REVISION
Post by Jora Lebedev on 08/06/12 at 20:22:49

I have the older style board with the newer Edcor transformer without the center tap.  It seems to be working, what will the 100 ohm resistors do?  Will it lessen the hum I'm experiencing with the amp?

Title: Re: ZKIT BOARD REVISION
Post by mboxler on 08/08/12 at 22:41:44

I just googled artificial center tap, and found this

http://www.el34world.com/charts/commonhookups.htm

The key statement I found was...

If you do not have a heater center tap on your power transformer, you must run two 100 ohm 1/2 watt resistors to ground to create an artificial center tap. If you do not have a center tap, you will get 120 cycle hum. Each 100 ohm resistor is soldered to one of the heater wires. The other ends of the 100 ohm resistors are twisted together and then soldered to ground.

Interesting????

Another article...

http://www.freewebs.com/valvewizard/heater.html

Mike

Title: Re: ZKIT BOARD REVISION
Post by GDSellman on 08/11/13 at 21:02:22

Thanks!  Will have a listen to the amp when done and then decide on the resistors.  Thanks again for the help!

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