# PDP-11/70 Boards

Rob Jarratt robert.jarratt at ntlworld.com
Wed Dec 8 17:14:02 CST 2021

```
> -----Original Message-----
> From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Mike Katz via
> cctalk
> Sent: 08 December 2021 22:58
> To: General Discussion: On-Topic and Off-Topic Posts
> <cctalk at classiccmp.org>; wrcooke at wrcooke.net
> Subject: Re: PDP-11/70 Boards
>
> More accurately up to it's rated wattage "Power = Voltage * Current"
> after all.
>
> If you have a 100W max variac you can draw 20A @ 5V (approx) but only 1A at
> 100V.

The problem is that it isn't marked with a wattage, just a current, which left me wondering at what voltage. Although Will Cooke's response seems to be that the voltage doesn't matter, so at 240VAC it would be 600W. Can that be right?

>
> On 12/8/2021 4:44 PM, Mike Katz via cctalk wrote:
> > "As a general rule, a variable transformer (Variac) can provide full
> > rated current at any output voltage. So a 2.5A unit can provide 2.5 A
> > at 1V, 10V, 120V, etc. With a 20V output, that is 50 VA (Watts, sort
> > of)."
> >
> > Up to the current rating of the variac.  When you draw more current
> > than the transformer can deliver then the voltage will sag.
> >
> > On 12/8/2021 4:22 PM, Will Cooke via cctalk wrote:
> >>
> >>> On 12/08/2021 3:58 PM Rob Jarratt via cctalk <cctalk at classiccmp.org>
> >>> wrote:
> >>> So, to supply the bricks on the bench, would a variac rated at 2.5A
> >>> be OK? I am not sure I know how much current the bricks will draw at
> >>> 20VAC, and at what voltage the 2.5A rating is given. Otherwise,
> >>> would this do the trick?
> >>> https://cpc.farnell.com/block/steu250-48/transformer-250va-230-400v-
> >>> 2-x/dp/TF01418?st=24v%20transformer
> >>>
> >>> Thanks
> >>>
> >>> Rob
> >>>
> >>>
> >>>>> JRJ
> >> As a general rule, a variable transformer (Variac) can provide full
> >> rated current at any output voltage.  So a 2.5A unit can provide 2.5
> >> A at 1V, 10V, 120V, etc.  With a 20V output, that is 50 VA (Watts,
> >> sort of).
> >>
> >> Will
> >>
> >> "I was born not knowing and have had only a little time to change
> >> that here and there."
> >> Richard Feynman
> >

```