[ARC5] S+N/N ratio results..more.

[Kenneth G. Gordon]

On 16 Jun 2013 at 13:55, Brian Clarke wrote:

> Hello Ken,
> 
> What adjustments did you make for the different G1 operating points?

Absolutely none.

> Gain is 
> related to the operating point - it is not an absolute independent of 
> operating point.

Yes.

The first thing I am trying to learn is exactly what advantage there is, if any, to simply 
substituting a tube with a higher transconductance into the radio without doing anything to the 
circuit.

So far, it doesn't look there there is much, if any.

> As I read the circuit, the Align Input capacitor compensates for 
> inter-electrode capacitance to achieve resonance with the RF input coil.

Correct.

Which is why I cannot peak the 12SH7 the way the receiver RF amp grid coil is aligned at 
present.

Even with the 12SK7, the Align Input peaks with the capacitor almost all the way open. It 
should be 1/2 open at the high end of the band, and isn't.

I'll have to adjust the slug in the RF amp grid coil before proceeding.

The next step (after the above) is to make G-1 bias adjustable and set it according to the 
manuals to see what, if any, improvement there is when substituting tubes.

Another problem has cropped up: if I substitute the 12SK7 in the first IF with either of the 
other two tubes, the stage will break into strong oscillation at certain settings of the IF amp 
grid trimmer.

I'm going to "operate" on the RF amp first and leave all the rest of the circuit strictly alone for 
the time being.

Ken W7EKB