On 25/01/16 11:07, Ian Jackson wrote:

...
Is backlash in tuning mechanisms necessarily a problem, because
a little bit of looseness in the drive means that an accidental nudge of
the
tuning control won't cause a frequency change, as it would if
tightly-coupled and backlash free?




you trained for backlash on a Trio 9R59D ...

A good training ground, as it also suffered from considerable drift.

In the late 60s, an SWL lived a couple of doors from me, and he had a
9R59D. I spent quite some time rebuilding a lot of the VFO - better
capacitors, stouter wiring and, of course, I also fitted the 'optional'
neon stabiliser. It appeared to be a lot better. A few weeks later I
asked him how he was getting on with it - only to find that he had sold it!

I did similar modifications to mine, plus adding a crystal marker. It
was much better afterwards.

I don't think the 9R59 was especially poor in terms of backlash for
equipment in that class. As I recall, it had a 'cord and pulley' system,
rather than a geared one, and provided the cord was in good condition,
followed the correct path (a common error when re-cording was it
'invent' a new route), and the tension was right, it wasn't bad- for a
receiver of that standard. I recall repairing a Heathkit Rx (I think a
Mohican) for and SWL, he bought it S/H, supposedly working. It lit up
but little else. The soldering was a nightmare. There was a note in the
handbook that the dial cord route had been 'improved'. An interesting
use of the word improved. Even when corrected the tracking wasn't all it
could have been. Eventually I got that right but the tension was a real
pain to get just right. Another, similar pain, was a Codar CR70 which
someone had 'got at' and the same SWL had bought, supposedly working.
Both had been 'Bring and Buy' purchases at a rally.
Eventually, he got a pristine FRG7 for next to nothing at a silent key
auction. While it looked pristine, it was sold as not working and went
for peanuts. It turned out there was a dry joint in the PSU.