[Heathkit] tubes in the HW101 - use the 6AH6

[Kenneth G. Gordon]

On 3 Mar 2009 at 19:12, Mark Nace wrote:

> Hi everyone,
> I seem to remember that a while ago, some were saying that the 6AU6
> could replace the 6HS6 in the HW-101, and after realignment it will
> work okay.  Same base diagram, and roughly the same characteristics,
> and are both sharp cut-off (I think). 

The 6AU6 was the ORIGINAL tube that Heathkit used in 
the RF amp and 1st receiver mixer (V-10 and V-11) in the 
SB-100/101 and HW-100/101, so, of course you may use 
them there.

However, Heathkit then changed to the 6HS6 in both the 
HW-101 and the late SB-101s and 102s, because that tube 
has higher gain and much lower noise than the 6AU6.

Alignment will not change much in going back to the 6AU6.

But, I discovered quite some time ago that the 6AH6 can 
also replace the 6AU6 AND the 6HS6, via a suggestion 
from Glen Zook concerning replacing the 6AU6 with one in 
the VF-1.

The 6AH6 is far easier to find (the military used thousands 
of them), far cheaper, and much more rugged.

Furthermore, its gain and transconductance are very similar 
to the 6HS6, and while the 6HS6, in this service, is 
operating pretty much at its maximum ratings, and thus 
doesn't last very long, the 6AH6 is running very 
conservatively and thus lasts a long time.

I use the 6AH6 in the RF and 1st receiver mixer (V-10 and 
V-11) of all my SB/HW multi-band transceivers and am 
very satisifed with them.

One thing you must remember, though, is that BOTH the 
6HS6 and the 6AH6 require more filament current than the 
original 6AU6, so, if you are going to replace the 6AU6s, 
you have to replace BOTH V-10 and V-11, not just one or 
the other, or the filament system will become unbalanced.

So, in short, yes, you may use the 6AU6 in place of the 
6HS6, but I much prefer the 6AH6 in the RF and 1st 
receiver mixer instead, and if you try them, I think you will 
too.

Ken Gordon W7EKB

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