[Boatanchors] [Glowbugs] Hallicrafters HA-5 VFO...

[Bill Cromwell]

On Mon, 2013-01-21 at 01:06 -0600, Sandy wrote:
> Has any one replaced the 6U8 withy a 6EA8 or similar tube?  Did this
> help the overall stability of the VFO?
>  
> Also looking for mods to slow down the drift of his beast!  Looks like
> it would be  good driver for the Drake 2NT if it could be stabilized!
> I hate trying to reinvent the wheel if someone else has already done
> it!!!
>  
> I can live with the lack of mechanical problems, as it is typically
> “Hallicrafters” lo tech design.  What I interested in is “anchoring”
> the thermal drift to a reasonable rate!
>  
> Suggestions or practical solutions anyone?
>  
> 73,
>  
> Sandy W5TVW

Hi Sandy,

I have some experience with overly drifty VFOs and often it can be a
matter of the individual oscillator tube or it's buffer (if it has one).
That doesn't mean a change of tube type but a change to a different tube
of the same type. The dramatic example in *MY* shack was a 6C4 in a
Hammarlund receiver. The tube checked good but the radio was really poor
(useless) due to so much drift. I had several other 6C4s in the
inventory and I started swapping them into the receiver. Most of them
were very good and the one I kept in there settled down after about a
two minute warmup!

Changing to a different type can sometimes make a difference. An example
of that is replacing a 6AU6 oscillator with 6AH6. That made a big
difference in one DX-100 but no difference at all in my Johnson Ranger.
YMMV. I think the tube you are considering (I haven't looked) has the
same pinout and can be a drop-in replacement. Check the heater current
requirements - don't overload the power supply. If it works - great. You
can also try different 6U8A tubes.

73,

Bill  KU8H