[time-nuts] Thunderbolt - any negatives ?

Mike Monett xde-l2g3 at myamail.com
Sat Jun 20 03:28:19 UTC 2009

  > Mike,

  > That PS is a most curious problem. For reduced leakage fields from
  > 60Hz transformers,  it  was  common to have  a  wide  copper strap
  > wrapped around  the  transformer in the  same  orientation  as the
  > windings.

  > This strap was the full width of the winding bobbin, but  formed a
  > shorted turn  on  the  outside of the  transformer  to  reduce, or
  > eliminate leakage flux.

  > Does your  tranformer have this shorted turn on it &  is  it still
  > shorted?

  > Any chance your line setting is 100V? This would certainly run the
  > transformer towards  saturation.  Can you power that  unit  from a
  > Variac &  set the voltage down enough to see  the  external fields
  > slack off?

  > H-P had  a rather conservative limit on external  fields  at power
  > line frequeny  &  this was  always  verified  during environmental
  > testing, so I'm quite surprised you're seeing this issue.  I think
  > something is broken.

  > Pete Rawson

  Hi Pete,

  I remember  the copper strap from my younger days repairing  tv sets
  for my neighbors. That was a long time ago:)

  The power  transformer  on the 53310A is huge - way  bigger  than it
  needs to  be  for  the load. But I don't  recall  seeing  the copper
  strap. As I recall, all four sides of the transformer were visible.

  I thought  that was quite odd as I was expecting to  see  the copper

  Part of  the  problem  is the TEK 2467B  is  extremely  sensitive to
  magnetic fields.  The crt has a channel multiplier to  allow viewing
  single-shot events  at 1ns/div like the TEK 7104. So  the deflection
  sensitivity is much higher than normal.

  The problem is definitely due to stray magnetic fields. The only way
  to have the two instruments turned on at the same time is to put one
  on a  different  bench. That is a bit awkward when you  need  to run
  back and forth to adjust the controls.

  The line  voltage  is   125V,   so   that's  not  the  problem. Both
  instruments are  pristine  inside and seem to be  working  fine. The
  2467B doesn't seem to be affected by any other instrument except the

  Another small  point.  I mounted a fluorescent light  under  the top
  shelf where  the  TEK 2467B's sit. It turns  out  the  small ballast
  inductor for the fluorescent light also delivers enough  stray field
  to demolish the 2467B.

  I solved  the  problem  temporarily by  unscrewing  the  ballast and
  letting it  hang down about 6 inches, supported by  the  leads. It's
  been like  that for a long time. I was just looking at  it  now, and
  remembered that I promised myself I would mount it properly  as soon
  as I had some time.

  So I  think the 53310A is OK - maybe just a bit stronger  field than
  usual. And the TEK is indispensable, so I just have to find  ways to
  keep the stray fields away from the scope. BTW, both scopes show the
  same problem, so it's likely intrinsic to the design.


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