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Old 4th Feb 2019, 11:26 pm   #24
ms660
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Join Date: Apr 2011
Location: Cornwall, UK.
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Default Re: Ferrograph 4A: Restoration advice needed

n will be far less than 30, n is the turns or voltage ratio not the resistance ratio.

Eg: Let's assume that the transformer is on the 245 volt tap with 245 volts going in, therefore Vp = 245, Total Vs anode to anode (according to the manual) = 480 VAC therefore divide that by 2 which = 240 therefore n = 245/240 = 1.02 therefore n = 1.02

Rt = Rs+n squared*Rp…..(+ R1) R1 is any additional surge limiter that may be fitted, that can be omitted because none is shown in the schematic.

Rs = 210 (420 as measured/2) Rp = 7 (as measured) and n = 1.02

So, Rt = 210 + 1.02*7 = 217.14 Ohms for each leg or 2 X 217.14 Ohms if you like.

So far as I can make out.

Lawrence.
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