[ARC5] Quick sensistivity comparison

[J. Forster]

Ken,

It might be worth checking for gas in the tubes.

I'd suggest running them for several days at nominal filament, nominal
plate, and biased to conduct about 10-20% of rated plate current to allow
the getter to clean up anything that has diffused into the tubes in the
last 70-odd years.

After that, try the NF test again.

YMMV,

-John

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


> Ken,
>
> you don't say what you were surprised by?   I am surprised that /any
> /valve HF receiver gives apparent sensitivities this low (either set),
> and would suspect leakage from your signal generator.
>
> Either way, both sets of figures (if accurate) are academic. Aerial
> noise on the HF bands will swamp these figures by some 10 - 20 dB.
>
>
> Richard G7RVI
>
> On 13/06/2013 08:04, Kenneth G. Gordon wrote:
>> RF gain max. AF gain low. Radio Shack CB speaker with 500:8 ohm
>> transformer. Audio
>> impedances are not properly matched, but there is still ample audio.
>>
>> 12SH7: AM 0.3 microvolt modulated 400 Hz at 30% clearly heard.
>>               CW 0.1 microvolt clearly heard.
>>
>>
>> 12SK7: AM 1 microvolt, same conditions as above, heard mixed with noise
>>               CW 0.3 microvolt, heard, mixed with noise
>>
>> Signal generator: HP-8640B fed to receiver through a 50 ohm terminator.
>>
>> I must admit to being surprised.
>>
>> Ken W7EKB
>> ______________________________________________________________
>> ARC5 mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/arc5
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:ARC5 at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>