[R-390] Waking up my non-A

[John Lawson]

On Fri, 6 Jan 2006, David C. Hallam wrote:

> In spite of all that has been written in various reflectors, etc. and
> conventional wisdom aside, it is not a good idea to "bring up slowly with a
> variac" a vacuum tube radio.  Vacuum tubes will not conduct until the
> filament temperature reaches design temperature (or close to it).  Nothing
> good can come from letting the tubes try to operate at a low line voltage
> for any extended period of time.



   This is advice well-grounded in the physics and dynamics of vacuum tubes 
- and the point is well-taken. Having done a bit of vacuum tube design 
myself, and I mean the design of a couple of thermionic devices, as well 
as many years of involvement with the circuitry of same - I understand the 
fundamentals of your post.

   That being said...  I am also guilty of 40 years of 'soft-starting' gear 
that has been dormant for unknown periods of time - and I honestly cannot 
recall ever having anything sustain damage from that process alone.  Now, 
most certainly I've blown up my share of gear - have various scars and 
fancy anecdotes of those 'events' - and I have had more than a few devices 
complain bitterly (and spectacularly) when I *didn't* take my time... 
however nothing in my experience has ever had a failure that I could 
atrribute to overall low system voltage, or due to poor space charge 
formation or low electron flux because of insufficient heater temps...


>
> If you want to reform electrolytics in place, risking your power transformer
> in the process, you can remove all of the tubes and replace the rectifier
> tubes with ss diodes.  Then raise the voltage slowly with a variac.
> Fortunately the R-390 doesn't use an electrolytic in the power supply.
>

   That's what the 0-5 AC Ammeter and the 2A Heinemann QB circuit breaker 
is for...  ;}

  I certainly don't just crank 'er up and then wander off - I try to pay 
fairly close attention to the process.  So far, I seem to have been pretty 
Lucky.


    Thanks for the note, Dave, and Happy New Year!


Cheers

John  KB6SCO