[Hallicrafters] R-274D/FRR - Concerning a circuit mod

[Rich Hebel]

I am restoring a R-274D/FRR.

 

I am trying to reconcile the actual unit to the schematics.  There are
clearly a couple of non-factory mods.

 

One of them has me a little puzzled.  

 

According to the manual, filament power to the VFO and 1st Mixer is fed
from the main power transformer through a ballast tube and then on to
the filaments.  

 

In the unit I have, someone has replaced the ballast tube arrangement
with a bridge rectifier and a pi filter.  I guess I can understand why
someone might put a DC supply to the filaments.  However, in series
between the output of this supply and the filaments is a device I need
some help with.  It is a black metal can, about 1" diameter by 1.5"
tall, with an octal pin base.  The only markings on it are "JD" and
"S-5251" and a small graphic that looks kind of like the schematic
symbol for a diode with a symbol for a fuse overlapping it.  Does
anybody have any idea what this is?  It is a two terminal device, with
pins 1 and 7 connected.  No other manufacturers ID or markings are
present.

 

Any help would be appreciated.

 

Tnx

 

Rich AA7P 



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