DRIFTING HW-101

[Michael Waldrop]

As for the drift being caused by the VFO, Ken is correct.

I doubt the heterodyne oscillator and/or the carrier generator,
CW/TUNE/USB/LSB, oscillator(s) are the cause of the drift.

Sometimes, not always, changing V20 "6AU6" VFO tube help
will reduce the drift. However, it may take one or more tubes
to find one that reduces the drift.

Check the voltage on pin 5 and 6 of V20, the VFO tube. The voltage on the
rear VFO B+ pin should be 150VDC. Pins 5 and 6 of V20 should be
149VDC.  If the voltage varies then check V18, an OA2 voltage regulator
tube.

V18 regulates the VFO's 150VDC B+, obtained through the voltage drop across
R304 and R305 (1K 7 watt and 2.5K 7 watt) resistors from the 300 VDC B+ on
pin 3 of the rear power connector.

Q942, a 2N3393 zener, may also need replacing. Q942 regulates the VFO's
V20's negative cathode voltage.

The VFO resistors should also be checked. Age will cause them to change
values, usually increasing in resistance. Change any that fall out of
specified tolarances.

The VFO's NPO temperature compensating capacitors could be causing the
problem. There's no easy way to check them.

Don't discount the power supply. The capacitors and resistors in the
HP series power supplies are quite old and can cause voltage variations.

Some food for thought. Have fun.

73's
Mike
W5RKL






On Sun, 17 Jun 2007 18:24:05 -0700, Kenneth G. Gordon
<kgordon2006 at VERIZON.NET> wrote:

>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
>
>-----------------------------------------------------------
>Products bought, sold or traded here is the responsibility of the
>parties involved.  This list and the City of Tempe are not responsible
>for losses or misrepresentations of any kind.  Buyer beware!
>
>-----------------------------------------------------------
>This list is a public service of the City of Tempe, Arizona
>-----------------------------------------------------------
>
>Subscription control - http://www.tempe.gov/lists/control.aspx?list=HEATH
>To post - HEATH at LISTSERV.TEMPE.GOV
>Archives - http://listserv.tempe.gov/archives/HEATH.html

-----------------------------------------------------------
Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.aspx?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://listserv.tempe.gov/archives/HEATH.html