[ARC5] Fw: Receiver current drain

[J. Forster]

Henry,

I have not analyzed the circuit and don't have the specs on the
transformer, without which it'd be pretty hard to figure it out. You can,
of course, figure the transformer's dissipation from the primary
resistance and plate current.

Frankly, contrary to much "ham lore", I firmly believe the original
designers of these (and virtually all other) military radios knew
precisely what they were doing. They were at war, and lives depended on
the stuff working.

YMMV,

-John

=============

> Thanks for the warning John. Thought there had to be a minus side.
> Would a more moderate resistance decrease be a workable solution?
> I haven't taken note of how much reduction was originally suggested.
> Suppose the original value was chosen for optimum performance/linearity
> and longevity of the 12A6.
>
> Best wishes,
> Henry
>
> PS- My emails to you bounce when I use this address but get through via my
> yahoo address
>        -guess you'll see this via Cc: ARC-5
>
>
> ----- Original Message -----
> From: "J. Forster" <jfor at quik.com>
> To: "Henry Mei'l's" <meils at get2net.dk>
> Cc: <arc5 at mailman.qth.net>
> Sent: Thursday, January 06, 2011 7:57 PM
> Subject: Re: [ARC5] Fw: Receiver current drain
>
>
>> Henry,
>>  I'm not so sure lowering the cathode resistor is such a good idea.
>>
>> The suggested change will roughly double the 12A6 plate current, and
>> hence
>> increase the dissipation in the output transformer primary by 4X.
>>
>> It also might saturate the transformer with excessive DC, since the
>> radio
>> has a single ended output stage.
>>
>> Best,
>>
>> -John
>>
>> ==================>
>>> ----- Original Message -----
>>> From: "Henry Mei'l's" <meils at get2net.dk>
>>> To: "Mike Morrow" <kk5f at arrl.net>
>>> Sent: Thursday, January 06, 2011 7:32 PM
>>> Subject: Re: [ARC5] Receiver current drain
>>>
>>>
>>>>I also find that current drain varies from about 10-15 mA to 25-28 mA
>>>>depending on the B+ level.
>>>> Have also always found output sufficient for loudspeaker operation.
>>>> Nice
>>>> to know I can get more
>>>> output by changing the 12A6 cathode resisistance, if I should ever
>>>> need
>>>> increased audio.
>>>>
>>>> Henry. oz1uf - n2nr
>>>>
>>>>
>>>> ----- Original Message -----
>>>> From: "Mike Morrow" <kk5f at earthlink.net>
>>>> To: <ARC5 at mailman.qth.net>
>>>> Sent: Thursday, January 06, 2011 6:52 PM
>>>> Subject: Re: [ARC5] Receiver current drain
>>>>
>>>>
>>>>> >We must remember that in military service, this tube was driving
>>>>> >headphones
>>>>>>at the 100-200 mW level so there was no requirement to generate a
>>>>>> large
>>>>>>amount
>>>>>>of audio.
>>>>>
>>>>> Is that really true?  WWII-era aircraft interphone systems
>>>>> (pre-AN/AIC-2)
>>>>> did NOT
>>>>> amplify the audio of ANY receiver connected to the system.  They
>>>>> simply
>>>>> routed
>>>>> receiver AF outputs to each station box.  Bomber installations of,
>>>>> say,
>>>>> the
>>>>> SCR-274-N could worst case have ten headphones connected in parallel
>>>>> to
>>>>> the AF
>>>>> output of the receivers. (Though most stations would be usually
>>>>> selected
>>>>> to the
>>>>> interphone amplifier's AF output, itself usually a simple one-tube
>>>>> amplifier that
>>>>> amplified *only* microphone audio.)
>>>>>
>>>>> Apparently the AF output of the command, liason, and DF receivers was
>>>>> enough to
>>>>> meet the demand.
>>>>>
>>>>>>...some owners have in the past reported adequate audio output into a
>>>>>>loudspeaker
>>>>>>even with the original value...
>>>>>
>>>>> In the 1960s, I often used a BC-453-B to monitor maritime Morse
>>>>> around
>>>>> 500 kHz.
>>>>> I got adequate drive for a speaker by using an appropriate
>>>>> impedance-matching
>>>>> transformer.  No receiver AF tag modifications were required.  (I
>>>>> used
>>>>> a
>>>>> 240 vdc
>>>>> HV supply.)
>>>>>
>>>>> Mike / KK5F
>>>>>
>>>
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>>
>>
>
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