On Sat, 1 Dec 2018 19:27:11 -0800 (PST), John-Del
wrote:

On Saturday, December 1, 2018 at 8:45:43 PM UTC-5, Tom Biasi wrote:
On 12/1/2018 3:47 PM, wrote:
To All,
I need to power an amp that draws just under 1.5 amps at 110 volts.
I measured the current it draws when powered from my variac. The
voltage to the amp should be within 5% according to the documentation.
The voltage in my house measures 122 volts to 126 volts, varying
during the day. So bucking 12 volts should be fine.
I am looking at a 120 volt to 12 volt center tapped 5 amp rated
xmfr at PartsExpress. The VA of the xmfr is not listed in the
description. I want to connect this xmfr in buck configuration. Since
I will be bucking 12 volts at approx 1.5 amps this equals 18 VA. At
least that's how I remember how to calculate VA from connecting big
buck xmfrs to one of my machines several years ago. I think the 12
volts at 5 amps secondary means that the xmfr is 60 VA. But I'm not
sure because it is center tapped. It shouldn't make any difference,
right? If I used the center tap and just bucked 6 volts then the VA
rating would be 30, wouldn't it?
Thanks,
Eric

If all the 110 volts does is make DC why can't you just clamp the DC?



What if it's a tube amp?

It's still easier to add a buck transformer than add a regulator circuit (not a great idea to "clamp" the DC).
You got it John. I should have mentioned that it was a tube amp, I
gues.
Eric