[R-390] SS VR replacement for 3TF7

[Tim Shoppa]

Flowertime01 at wmconnect.com wrote:
> An idea back when was to just stuff a silicon diode rated at 1amp and 
> 100volts into pins 2 and 7 of the 3TF7 socket.
>
> This blocks the 25.2 volts 1/2 of  the time. The net effect is 12.6 volts of 
> DC.
> No 3.6 watts of heat to radiate.
> The transformer gets a 1/2 cycle rest.

Not exactly.  Look up "RMS".  Sqrt((25.2**2)/2) is not the same as 
Sqrt(12.6**2).  Putting the diode in series gives you effectively
17.8V worth of heating (ignoring diode drop...)

We've been through this at least three times before on the
list in the past couple of years...

Or did I again fall for the purposely-mistaken-fact-to-make-a-point?
I'm always falling in that trap!

> I live with real weather and when my lights blink, I do not set and wonder 
> why my receiver is drifting off frequency.

For fun, pull the ballast tube and count how many seconds until you
start hearing the beat note drift. My ears may not be as sensitive as
when I was young but it's many seconds until I hear the drift from
zero filament current!

> Why have we not heard about this approach before?
> Read some of the other mail from today.

I've seen it before many times over the past couple of years... again
I think I fell for the trap!

Tim.