[AMRadio] WTB/WTS and a question

Brian K Harris brian.k.harris at philips.com
Fri Dec 30 11:21:15 EST 2005

Good Morning,

1.  I would like to buy or swap for two solid state plug-in replacements 
for the 872A mercury vapor rectifiers for my KW-1.  Enuf said.

2.  I am restoring a broadcast/shortwave radio set for my brother.  It is 
an RCA 8BT, battery operated 'farm set' from the 30's.  In addition to 
using three 45V batteries in series for the 135V B+, it used four small 
1.5V cells for biasing the 1st detector and the 1st and 2nd IF's, and a 
multi-tapped battery to get 3V bias for the 2nd detector and 7.5V bias for 
the audio driver.  As my brother doesn't live on an electricity deprived 
farm, I am building a solid state AC supply to meet those needs.

The tubes all have 2V filaments.  The radio has two inputs for a filament 
supply, 2V or 2.5V (the 2.5V input merely inserts a series resistor).  My 
question is....why did anyone manufacture 2V filament tubes and what kind 
of battery put out 2V or 2.5V?  I am building a solid state supply for the 
2V requirement as well so the question is merely to satisfy my curiosity.

By the way, this set uses a pair of push-pull 49's for the audio output 
stage.  These are zero bias tubes in Class B with 3.5W capability.  Very 

Thanks for reading,

Brian WA5UEK

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