Steve, most all 240v/120v capable amps series up the dual primaries and when
strapped for 240v the CT formed by the series primary create a neutral for 120v
items. Only old Herry amps didn’t do that, but it’s no problem to run the
jumper over to that wire seeking neutral from the series primary CT. That
eliminates the need for the neutral you don’t have.
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On Thursday, May 6, 2021, 9:57 AM, Steve London <n2icarrl@gmail.com> wrote:
On 05/06/2021 01:03 AM, gudguyham via Amps wrote:
> Some of the old Henry amps actually require a neutral to be present when
> using the amp on 240v. On 120v it makes no difference because if you have
> two wires, hot and neutral (120v) the neutral is available. When switching
> to 240vac if you lack the neutral, they instruct you to use ground to carry
> the fan, and low voltage transformer neutrals. This practice is NOT good and
> could be dangerous. The neutral that is required is hooked up to a separate
> terminal at the rear of the amp, this is the neutral being sought out by the
> fan and LV transformer. The simple fix which satisfies all conditions is to
> NOT use ground( the green wire) to this terminal as a neutral, but rather use
> a jumper wire at the two terminals that series up the dual primary to that
> terminal. By doing this there is no need for an external neutral and the
> green wire can be used as chassis ground as intended.
If I correctly understand what you are saying, this is exactly what the Alpha
76
and my old B&W PT-2500A have done. They have dual 120 volts primaries that they
put in series for 240 operation. 120 volts for the blower is derived from one
side of a 120 primary and the "center tap" between the two 120 volt primaries.
73,
Steve, N2IC
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