[Hammarlund] Hello list - HC-10 and 6AU6s.

[Kenneth G. Gordon]

On 2 Apr 2012 at 12:10, Richard Knoppow wrote:

>      The 6AU6 and 6BA6 have virtually the same 
> transconductance with equal plate and screen voltages.

Although I have not been able to get to my tube databooks, I distinctly 
remember the 6AU6 having higher transconductance than the 6BA6.

The 6AU6 is routinely used in oscillators (especially VFOs), while I don't 
know that I have ever seen a 6BA6 used as such. Perhaps the differences 
are only inter-electrode capacitances and the transconductances under 
identical conditions are the same, or close enough to it.

I'll have to wait until I can get to my tube data-books before I can comment 
further.

> The 
> 6AU6 has no advantage over the 6BA6 where the design calls 
> for the second.

Agreed.

>  The 6AH6 has about double the 
> tranconductance of either of the others but is a sharp 
> cut-off tube like the 6AU6.  

Yes, and in my experience has proven to be a much better tube for use in 
VFOs (and in the RF and mixer stages of such rigs as the SB-101) than the 
6AU6.

I much prefer the 6AH6 as an oscillator over the 6AU6.

>The increased gain may cause 
> problems where its not designed for.

Yes...as I pointed out...

> In a SSB adaptor like 
> the HC-10 the signal levels are high enough so that tube 
> noise is of no consequence anyway plus its all at low 
> frequencies.

Yes.

>      These are good converters and rare as hen's teeth.

Yes. I have wanted one for a long time...

Ken W7EKB