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

[Kenneth G. Gordon]

On 1 Apr 2012 at 22:29, David  Thompson wrote:

> Al, W8UT says the list needs more traffic and I have not been on the
> list since the original reflector in 1998.
> 
> I just got a HC-10 SSB adapter and started checking it out.  I will
> have more questions later but for now wonder why a previous owner put
> 6AU6's in both IF's which call for 6BA6's.

Probably because the 6AU6 has much greater transconductance, and 
therefore lower noise and greater gain.

However, since it is a sharp-cutoff tube, it will royally screw up any AGC 
applied to it, and therefore makes the circuit much more prone to overload.

Also, in my experience, they are not particularly reliable either.

When a circuit calls for 6AU6s, I always use 6AH6s or the military 
equivalents thereof. Those are far more reliable, cheaper, more available, 
and are somewhat closer to being "semi-remote cutoff" types.

Even so, IMHO, I would never use either of those in the HC-10's IF strip.

As far as I know, all of the above tubes have the same base-connections and 
are direct plug-in substitutions.

If I had your HC-10, I would go back to 6BA6s before I did any tune-up or 
restoration of that adapter.

There was an excellent article in the latest issue of ER Magazine on the HC-
10, BTW.

Ken W7EKB