[ARC5] 10 meter BC-454 - more

[Geoff]

> On 23 Feb 2013 at 20:21, Dennis Monticelli wrote:
>
>> Ken,
>>
>> Sounds like the 12SK7 is delivering more gain but the S/N ratio (i.e.
>> sensitivity) is unchanged.
>
> I read it differently: it has the same gain, or close to the SG7, but it 
> also puts
> out a lot more noise.
>
> Ken W7EKB
>

Which is correct since it is the ENR contribution that establishes a tubes 
NF. Anything else is RF resistance thru the circuitry adding to it to give 
you stage by stage or system NF.
 In your case it is likely the 12K8 you are hearing and the 12SK7 doesnt 
have enough low noise gain to overcome it.
A 12SG7 as first IF may help a little, I can hear a small 10M improvement in 
a HQ-129X with a pair of 6SG7's in RF/IF and 6K8 converter but that is thru 
a bandswitching rats nest.

With no bandswitch and short leads your set should be capable of  ~ .7uV for 
10dB SNR on AM which is a little worse than the NC-240D on 10M. It is hard 
to beat almost zero lead length and heavy wire coils plus the 6K8 is used 
just as a mixer.

Carl



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