[HBR] 85Khz IF Transf.

[Hopperdhh at aol.com]

Hi Pete,
 
Tapping the grid or plate down on the coil will unload the coil and raise  
the Q of the circuit.  The tubes have roughly 1 Megohm input and output  
impedance which sounds like a lot, but these are high impedance circuits.   Reducing 
the stage gain helps the amplifier to be more stable and generally  behave 
better.  There is less chance of regeneration which can spoil the  shape of the 
response.

The only things bad about the ARC-5 coils are  their large size and 
relatively low Q compared to the Miller coils.  But  that can actually be a good thing 
-- especially for AM phone reception.   And, as was pointed out earlier, you 
can loosen the coupling to improve the  selectivity for CW.
 
I have used the VLF ARC-5 behind a crystal converter, and together they  make 
a great receiver.  I would connect the transformers just like  they were 
originally intended.  In fact, I think 6BA6's or 6BJ6's would be  OK for IF 
amplifiers.
 
BAMA has a complete manual for the ARC-5 equipment under "military."
 
73,

Dan K9WEK


In a message dated 12/11/2008 11:31:46 A.M.  Eastern Standard Time, 
radioconnection at gmail.com writes:

I'd be interested in hearing about the taps and their purpose as well.  I've 
read that they were used to reduce stage gain; and I'd suspect they might  
also reduce the loaded Q of the coils? Does anyone have a definitive  answer?  I 
plan on using 6EH7s in the IF stages, and I might need to "burn  up" some 
gain...

Pete
 
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