[Boatanchors] Diode in Filament supply line

[Philip Atchley]

Hi Wayne et al,

I've not seen this particular application, but I can reason it out.  It's 
like using a diode in series with a soldering iron to lower it's operating 
temperature, something some of the inexpensive "dual heat" irons from places 
like the "Cell-Phone Shack" used.   I call them that because I can't even 
buy a plain old PL-259 plug or a chassis mount DC barrel connector at the 
local store now.  "We'll mail order them for you".

Anyway, the reasoning is that so long as there isn't a filter capacitor, the 
"effective" Voltage across the load of a half wave rectified  AC Voltage is 
half that of the AC Voltage (assuming a purely resistive load).  HOWEVER, 
there is a couple of big "gotchas" here.

1.  The filament current draw of 6JB6's will be twice that of the 12BJ6's. 
I 'suspect' that since current is being drawn during only half of the cycle, 
load (heating) of the transformer may be similar. But without doing the math 
that's only speculation.

2.  "Peak" Voltage from the 12 Volt source across the load will be twice 
that of a 6 Volt source, but in the case of a resistive load with a long 
time constant (Filament) it's probably not a factor.

73 de Phil,  KO6BB
DX begins at the noise floor!

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Merced, Central California,    37.3N  120.48W  CM97sh


>
> Good Evening
>
> I obtained a TR3 that was DOA. One of the things that I found was that it
> had 6JB6's in the final instead of 12JB6's and a big diode was wired in 
> series
> to the 12vac filament line to those tubes. Anyone ever see this method of
> making  a 6v filament work in a 12v application?
>
> 73,
>
> Wayne
>
> VE3XAZ/WA7LZC