[R-390] SS VR replacement for 3TF7

[Cecil Acuff]

My Favorite is a piece of Teflon coated aircraft wire with a couple of Mil 
spec RS-232 male crimp pins installed, shoved into the socket in the 
appropriate place and a pair of very common (read cheap) 12BA6's in place of 
the 6V versions.  It don't regulate but neither does the resistor....not in 
the same way as the ballast tube.  The ballast tube absorbs voltage changes 
by varying it's resistance and corresponding voltage drop....something a 
resistor can't do.  In fact I would think the tubes are ballasting the 
resistor in that method of substitution....but it does work acceptably....as 
does the jumper and 12V tubes.

Cecil....
----- Original Message ----- 
From: <Flowertime01 at wmconnect.com>
To: <r-390 at mailman.qth.net>
Sent: Tuesday, January 03, 2006 6:29 PM
Subject: Re: [R-390] SS VR replacement for 3TF7


> DW Holtman,
>
> 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.
>
> As long as you are poking stuff in the socket add a filter cap.
>
>
> We will get yada yada yada all week for my use of the S word.
>
> Yes, a regulator may offer better performance if the power line shifts.
>
> I live with real weather and when my lights blink, I do not set and wonder
> why my receiver is drifting off frequency. As I am not an OP trying to get 
> a
> copy these days. When my receiver drifts I get the head sets off and look 
> out my
> window. There is more to life than my receiver and I would like to 
> continue to
> enjoy life. My QTH is not a bunker these days. Power line shift is my 
> first
> clue to bad weather.
>
> Tubes are getting costly. So some do not want to run them on DC filaments
> because some 1920 - 1950 text books suggest DC filaments tend to burn open 
> at one
> end and thus give tubes a short life. We will likely toss the tube for 
> noise
> before we burn its filaments open operating it on DC.
>
> DC filaments with no filter are more noisy than AC filaments. This could 
> be.
> But some filter caps would go a long ways. Maybe DC filaments are better 
> for
> noise if the source is filtered.
>
> Any way the idea has been presented before. It does work.
> Is it better? I do not know. Is 31 flavors of ice cream enough? What 
> flavor
> is best?
>
> Why have we not heard about this approach before?
> Read some of the other mail from today.
>
> Roger AI4NI
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