[AMRadio] Incorporating AM Ceramic Filter In Tube Radio


K5MYJ macklinbob at gmail.com
Sat Jan 3 13:56:16 EST 2015


Why do you need an AM filter? What is the radio you are trying to modify?

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"
----- Original Message ----- 
From: "Byron Tatum" <bjtatum1 at att.net>
To: <AMRadio at mailman.qth.net>
Sent: Saturday, January 03, 2015 10:33 AM
Subject: [AMRadio] Incorporating AM Ceramic Filter In Tube Radio


> Hello-
>  Can anyone suggest the best way to incorporate a 455 KHz ceramic filter 
> (impedance is 1500 ohms) into the IF amplifier chain of a tube receiver?
>  I wish to add the AM bandwidth filter (NTK LF-D6) at the start of my 2 
> stage 6BA6 IF amplifier chain. There is a pair of conventional type IF 
> transformers (each transformer has a pair of tuned circuits), the 
> transformer pair lightly coupled with a 2.2 pF cap.
>  The first 455 KHz IF transformer of this pair has its primary feeding B+ 
> to the second mixer plate circuit (6.0 Mhz to 455 KHz.) The secondary of 
> this first 455 KHz IF has one end grounded and the other end connected to 
> the 2.2 pF coupling cap. The other end of the coupling cap is attached to 
> the primary of the second 455 Khz IF transformer; the other end of its 
> primary winding being grounded. The secondary of this second 455 KHz IF 
> transformer is directly connected to the grid of the 6BA6 first IF 
> amplifier, with AVC feed (bypassed by capacitor) connected to other end of 
> secondary.
>  Can someone suggest the best manner in order to properly match the low 
> impedance input/output of ceramic filter with the minimum of loss?
>     Thanks, Byron WA5THJ
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