[Milsurplus] BA Tune-Up Without B+?

[Peter Gottlieb]

Can you use a reduced B+, say, 120 volts?  Reduces the hazard.  Then use the old 
trick of keeping one hand in your back pocket and insulating shoes.  No current 
path through your chest.


On 3/26/2016 5:54 PM, David Stinson wrote:
> Soon I'm going to need to tune the PA of a BC-669 transmitter.  If you've ever 
> seen one, you know
> this means opening covers, sticking your hand in where the B+ lives, fiddling 
> with a bunch of slides and etc.,
> and trying again about a dozen times per fixed frequency.
> Each time you hope and pay you remembered to turn
> off the B+.   Well, I'm old now and I will most certainly
> forget sooner or later.  I've already played that game and
> have the scars from it.  Don't think my weak old ticker will take many more 
> jolts.
>
> This is my idea- tell me if it will work:
> Remove all power from the transmitter.  Jam the PTT relay closed. Terminate 
> the antenna connector
> with a 50-ohm load.   (I know it's not designed for 50-ohms.  I'll be using an 
> external cap to fix that).
> Feed a hefty on-freq signal to the PA grids.  Put a scope across the 50-ohm 
> load on the output.  Fiddle for max voltage across the load.
> If I'm right, this will get the tuning pretty close and minimize fiddling with 
> it and skip having an early estate sale.
> Should work even backwards- feed a 50-ohm terminated
> signal genny into the antenna and put the scope on the tube grids.
>
> What do you think?
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