DRIFTING HW-101

[Kenneth G. Gordon]

On 17 Jun 2007 at 13:59, Kent Kressenberg wrote:

> Hello to a MOST helpful group...
> 
> I have a nice HW-101, acquired from a guy on list a few months ago,
> working great and very stable until recently I note an increasing
> tendency to drift from set frequency, even after ample wam-up time...
> a guy called me on being off-freq less than 10 minutes into a QSO last
> night and the rig had been on for a couple of hours.
>  Where do I start... what do I look for? Is this something that
>  tube(s) replacement is likely to help, is alignment needed... what do
>  you think?

No. This sort of problem is usually in the VFO itself.

However, it MAY be in one of the crystal oscillators. I.e., the USB, LSB, 
or CW crystal, or one of the  heterodyne oscillator crystals

First of all, you need to check carefully to see if the drift occurs on ALL 
bands, or only on one particular band. If the drift is far worse on only 
ONE band, then that points to the heterodyne oscilllator crystal for that 
band.

If it is on ALL bands, then it is either the one of either USB, LSB, or CW 
crystals, or the VFO. If the drift occurs in only ONE mode, then it has to 
be the crystal associated with that mode.

If it occurs on ALL bands and ALL modes, then it is in the VFO.

In some cases it can be caused by the dual-Jackson Brothers verniers 
themselves.

In most other cases, it is caused by something in the VFO going gunny-
bag on you.

The VFO is quite simple, but there ARE enough parts in it that any one 
of them could be causing unwanted drift.

If the VFO is suspect, the first thing I would check is the NPO and temp 
compensating caps in it.

The next would be the FET oscillator transistor.

Then the transistor whose emitter-base junction is used as a voltage-
regulator.

Sometimes, if you have a SMALL heat gun with a very small tip, or if 
you can make one for a hair dryer, you can pinpoint the bad component 
by directing heat at specific components. Or you could touch the tip of a 
low-wattage soldering iron to those same components to see what 
happens.

Or a bit of ice, or component cooler, to specific components can also 
help pinpoint a bad component or area. The problem with ice is of 
course that it melts and leaves water. Component-cooler is safer in that 
case.

Good luck.

Ken Gordon W7EKB

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