[Hallicrafters] SX-71 question

[rbethman]

Hallicrafters did the same to the "ANL" tube even in the SX-101 MKIII.

They apparently had their reasons, but did not "detail" them in the 
manuals that they produced.

The instance of the SX-101 MKIII, uses the identical ohm and wattage 
rating/value as you have found in the SX-71.

Bob - N0DGN

On 12/9/2010 12:05 PM, Art Lebermann wrote:
> Does anyone know why the two diodes would be more sensitive to hum than the
> other tubes?  Any other possible reasons for running reduced voltage?  I
> suspect that there is another answer.
>
> ART
> W6REQ
>
>
>> [Original Message]
>> From: Carl<km1h at jeremy.mv.com>
>> To:<Hallicrafters at mailman.qth.net>; Asif Khan<hallicraftersx28 at aol.com>
>> Date: 12/9/2010 5:24:37 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 reducing the filament voltage to these tubes?
> 73,
> RT
> 6REQ