[time-nuts] Thunderbolt - any negatives ?
xde-l2g3 at myamail.com
Sat Jun 20 03:28:19 UTC 2009
> 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
> 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
> 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
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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