Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Watkins-Johnson, more like WTF?

Trying out this WJ tuner, it's supposed to tune 0.9 to 10 MHz and
convert it to their standard IF of 21.4 MHz. Works wonderfully.
Sensitive anyway. But the frequency readings are way off-- about 8
percent low on the low end, 12 percent low on the high end. So when
the filmstrip dial says "10.0" you're actually listening to 8.8 or
so.

As Lewis Black would say, that's f***ed up.

Normally I'd go tweak what every other SW radio has- a coil slug or
big series padder for the low end, a small drifty mica compression
trimmer for the high end.

But as John Belushi used to say "But noooooo".

This multi-kilobuck box does not seem to have a high-end trimmer.
And 12% is a bit much to assign to component drift. It's a LC
circuit, so the freq goes as the square root of the LC values. It's a
bit too much to assume the coil has drifted by 23%. Major
puzzlement.

No manual of course.

Any hints appreciated.

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Default Watkins-Johnson, more like WTF?

On Jul 13, 7:32 am, Ancient_Hacker wrote:
Trying out this WJ tuner, it's supposed to tune 0.9 to 10 MHz and
convert it to their standard IF of 21.4 MHz. Works wonderfully.
Sensitive anyway. But the frequency readings are way off-- about 8
percent low on the low end, 12 percent low on the high end. So when
the filmstrip dial says "10.0" you're actually listening to 8.8 or
so.


Normally I'd go tweak what every other SW radio has- a coil slug or
big series padder for the low end, a small drifty mica compression
trimmer for the high end.


Any hints appreciated.


Couple of questions:

Does it let you tune all the way to/from 0.9 to 10.0 (off the dial of
course)?
Or, is the entire band shifted downwards?
Or, chopped off at each end?
Does it look all OEM?


I have seen (once) a substitute tuning capacitor installed almost
perfectly in a radio that then displayed similar problems.

If the radio has been "moused" at some time past, a couple of coil
windings could be shorted.

WJ is still very much in business... you might ask them.

Peter Wieck
Wyncote, PA

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Default Watkins-Johnson, more like WTF?

On Jul 13, 6:52 am, " wrote:
On Jul 13, 7:32 am, Ancient_Hacker wrote:

Trying out this WJ tuner, it's supposed to tune 0.9 to 10 MHz and
convert it to their standard IF of 21.4 MHz. Works wonderfully.
Sensitive anyway. But the frequency readings are way off-- about 8
percent low on the low end, 12 percent low on the high end. So when
the filmstrip dial says "10.0" you're actually listening to 8.8 or
so.
Normally I'd go tweak what every other SW radio has- a coil slug or
big series padder for the low end, a small drifty mica compression
trimmer for the high end.
Any hints appreciated.


Couple of questions:

Does it let you tune all the way to/from 0.9 to 10.0 (off the dial of
course)?
Or, is the entire band shifted downwards?
Or, chopped off at each end?
Does it look all OEM?


It's not a constant difference, it's just maddeningly from 8 to 12
percent low. So it's not slipped dial couplings or tuned up on the
wrong side of the LO.


And the calibration sticker is broken on one of the 72 screws keeping
the VFO cover from flying off. But everything in there looks OEM,
good and untouched.

Guess I'll try fiddling with the coil slug, but like Vilma says on
Scooby-Doo, when entering a haunted house, "I don't have a good
feeling about this"

Maybe another clue, for a fancy dual-conversion radio the image
rejection is very poor, not more than 25db it seems. Odd.


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Default Watkins-Johnson, more like WTF?

On Jul 13, 8:30 am, Ancient_Hacker wrote:
On Jul 13, 6:52 am, " wrote:





On Jul 13, 7:32 am, Ancient_Hacker wrote:


Trying out this WJ tuner, it's supposed to tune 0.9 to 10 MHz and
convert it to their standard IF of 21.4 MHz. Works wonderfully.
Sensitive anyway. But the frequency readings are way off-- about 8
percent low on the low end, 12 percent low on the high end. So when
the filmstrip dial says "10.0" you're actually listening to 8.8 or
so.
Normally I'd go tweak what every other SW radio has- a coil slug or
big series padder for the low end, a small drifty mica compression
trimmer for the high end.
Any hints appreciated.


Couple of questions:


Does it let you tune all the way to/from 0.9 to 10.0 (off the dial of
course)?
Or, is the entire band shifted downwards?
Or, chopped off at each end?
Does it look all OEM?


It's not a constant difference, it's just maddeningly from 8 to 12
percent low. So it's not slipped dial couplings or tuned up on the
wrong side of the LO.

And the calibration sticker is broken on one of the 72 screws keeping
the VFO cover from flying off. But everything in there looks OEM,
good and untouched.

Guess I'll try fiddling with the coil slug, but like Vilma says on
Scooby-Doo, when entering a haunted house, "I don't have a good
feeling about this"

Maybe another clue, for a fancy dual-conversion radio the image
rejection is very poor, not more than 25db it seems. Odd.- Hide quoted text -

- Show quoted text -


Please keep me (us) posted on your progress. Wild question... have you
tried blowing air through the tuning end? Super *DRY* air, of course.

Peter Wieck
Wyncote, PA

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Default Watkins-Johnson, more like WTF?

Aha, success!

Turns out the little setscrews on the tuning capacitor shaft were very
loose. As were about six others. Just loose enough for a little
slippage, but tight enough to still rotate the shafts and act semi-
okay.

The poor image rejection? Two more very loose setscrews on the ten-
turn pot that tunes the front-end.

I should have noticed-- the 10-30MHz version of this tuner has brown
thread-sealer on all the setscrews and is spot on freq. For some
reason they didnt use any thread locker on this one.




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Default Watkins-Johnson, more like WTF?

On Jul 14, 8:20 am, Ancient_Hacker wrote:
Aha, success!

Turns out the little setscrews on the tuning capacitor shaft were very
loose. As were about six others. Just loose enough for a little
slippage, but tight enough to still rotate the shafts and act semi-
okay.

The poor image rejection? Two more very loose setscrews on the ten-
turn pot that tunes the front-end.

I should have noticed-- the 10-30MHz version of this tuner has brown
thread-sealer on all the setscrews and is spot on freq. For some
reason they didnt use any thread locker on this one.


Wowsers! All that, and it was mechanical after all. I'll bet you feel
much better about investing in that unit right about now!

Many thanks for the report, few actually do feed back. And a very good
lesson to all... check the obvious before delving into the obscure.

Peter Wieck
Wyncote, PA

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Default Watkins-Johnson, more like WTF?

On Jul 16, 8:19 am, " wrote:

Wowsers! All that, and it was mechanical after all. I'll bet you feel
much better about investing in that unit right about now!


Well, no. While it's built like a B-58 and cost almost as much per
pound, it's a lousy radio.
Before MOSFETS, you might recall, transistor front-ends were really
really lousy.
Lots of intermod. Add varactor tuning and you have a receiver only
a Govt purchasing agency could love.

I can just picture the NSA guys in the Moscow embassy, trying to
listen to Krushchev's car phone but it's drowned out by TV's Channel
4's "Lunch with Lenin".

Perhaps I can find a satisfiable buyer if they appreciate top-notch
looking mechanicals and electricals, with that clandestine cachet, if
not performing up to appearances.



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Default Watkins-Johnson, more like WTF?

Ancient_Hacker ) writes:

Before MOSFETS, you might recall, transistor front-ends were really
really lousy.


But that was an illusion.

Before FETs, people didn't know how to design with bipolars for
strong signal handling. They thought that since transistors used
so little power, that was the prime factor in design.

So then FETs came along, and they were touted as the solution to overloaded
receivers. And then MOSFETs came along some years later, and they were
seen as an even better solution.

But about the time MOSFETs hit in the late sixties, people were starting
to realize that bipolars could handle strong signals, if they were used
properly. The bipolars didn't, but how they were used did. Nowadays,
you rarely see MOSFETs, bipolars doing most of the work.

But you can't get good signal handling from bipolars if your prime
criteria is low current. But that's not unique to bipolars.

Michael
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