[Hammarlund] HQ-170A drift

[Guido Santacana]

I have not seen the problem resurface after the replacement of the 6C4s in
the 180s. It seems that the circuits are very picky about the condition and
age of these particular tubes. The components that have failed in my 180s
are resistors. The other components that deteriorate with time are the mica
caps embedded in the IF cans. Replacement of these caps is a major project.
The caps can be replaced with modern silver micas mounted outside the coil.
I wish hammarlund had done this instead of using the embedded caps.

73s

Guido KP4FAR

On Saturday, May 17, 2014, Jim Wilhite <w5jo at brightok.net> wrote:
> Out of curiosity I wonder if some of the components associated with the
oscillator circuit could have changed value enough to cause this problem?
Maybe the caps and TC caps in the circuit are now not the value they were
when the receiver was built.
>
> My recollection of the subject receivers is they were as stable as any
other receiver of the time after a period of warmup, usually 15-20 minutes.
 Some things that can cause the  problem is the coil forms expanding as
they warm even though the filament is on all the time.  Those forms are a
cardboard type and prone to absorbing moisture over the years, then the
heat drives the moisture out and problems start.  Also switch contacts can
develop some corrosion over the year.
>
> There are a lot of potential problems so I wonder if just changing the
tube fixes the problem, or does it resurface after a while.
>
> Jim
> W5JO
>
>
> -----Original Message-----
>
> the 6C4 replacement. It has worked on both of my HQ180s. It seems that
although the 6C4 works well as an oscillator in most rigs, it seems to have
some problems in the 170s and 180s.
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