[Boatanchors] NEED HELP ON IF FILTERS

[DCrespy@aol.com]

Dee,  

I am assuming first that this is not an image problem.  If it is, IF 
filtering won't fix it, a good front end alignment might.

If it is IF filtering:  My experience with collins 51J-x receivers (3 of them 
working in my shack) has convinced me that you only need mechanical (or 
ceramic) filters under the toughest conditions.  I prefer my 51J-3 (no mech 
filters) to my 51J-4 (mechanical filters) for 90% of my listening.  So, 
before attempting a mod, I'd be sure that the AGC is working right and that 
the entire IF is properly aligned.  (AGC problems can cause distortion that 
may sound like interference.)

If you must modify it, please, for subsequent owners, leave the IF 
transformers in place, and add the filter under the chassis.  There is 
nothing more disappointing than finding an otherwise nice radio, that is 
missing a non-standard OE part, like an IF transformer.   An R-390A 
mechanical filter should be easy to find for $30 or so, and manuals are 
available on line to show you how to wire it in.  But again, the HRO was a 
premium receiver in its day, and should not need the mod.  I think you'll 
find something is wrong with the radio, and the filter would just be a work 
around.  I'd check out the AGC and do a good IF alignment first.

Good luck and 73
Harry  KG5LO
Saline MI
:


> From: "Dee Almquist" <>
> 
> Started an interesting project. National HRO-50T. Real clean radio & has
> been recapped with new stuff. Got it working pretty well. Still have
> problems with 3 of the coils sets to do yet but radio senseitivity not bad.
> This is a very stable radio, almost no drift! However, it needs help in the
> IF. Since it is single conversion, adjacent channel rejection leaves
> something to be desired. Seems the easest way is a 455kc 8 pole filter @ 
> 6kc
> (and maybe another @ 4kc) for AM mode. Problem is the cost!!! Looking @
> 

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