[Hallicrafters] SX-71 question

[wa1kbq at aol.com]

It seems like if it was hum reduction it would need to be center tapped 
and connected to B- at the center.

Regards, Greg


-----Original Message-----
From: Carl <km1h at jeremy.mv.com>
To: Hallicrafters <Hallicrafters at mailman.qth.net>; Asif Khan 
<hallicraftersx28 at aol.com>
Sent: Thu, Dec 9, 2010 8:24 am
Subject: Re: [Hallicrafters] SX-71 question


National also reduced the voltage on the 6H6 and later the 6AL5, they 
used
4.3 Ohms. Dont know who came first as the SX-71 and HRO-50 both came 
out in
1949 but the SX-71 had 4 prodution runs ending in 1954 so was the 
resistor
in all of them?

Its interesting to note that altho the Radiotron Designers Handbook 4th
Edition of 1952 discusses the hum issue and methods to minimize it does 
not
mention the filament resistor.

Carl
KM1H



----- Original Message -----
From: "Asif Khan" <hallicraftersx28 at aol.com>
To: <Hallicrafters at mailman.qth.net>
Sent: Thursday, December 09, 2010 4:37 AM
Subject: Re: [Hallicrafters] SX-71 question


>
> In the absence of the resistor an objectionable  60 hz hum would 
appear in
> the audio.The resistor reduces the AC filament  voltage to the ANL 
tube
> thereby also reducing the AC hum .
> Nick
>
>
>
>
>
>
>
> -----Original Message-----
> From: Art Lebermann <artleb at earthlink.net>
> To: Hallicrafters <Hallicrafters at mailman.qth.net>
> Sent: Thu, Dec 9, 2010 1:32 am
> Subject: [Hallicrafters] SX-71 question
>
>
>
> he SX-71 schematic shows a 6.8 ohm resistor in the filament 
connections to
> V11
> 6H6 - AVC/ANL) and V12 (6AL5 - FM detector).  Does anyone know the 
reason
> for
> educing the filament voltage to these tubes?
> 73,
> RT
> 6REQ
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