[ARC5] Fw: Receiver current drain

[Henry Mei'l's]

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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>
>