Hi all,
My caps probably are bad. When I first got the scope
around 1980, I learned about "black beauties" and had to
replace them in the power supply, but I think I recall
being told that the bumble-bee types were fine, so those
stayed in. Now it looks like I have leakage from them in
the HV power supply. See the attached photo
here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781
The two shiny black 0.001 uF caps stand out because they
are coated in oil. You can't see it on the photo, but
there is a film of liquid oil between the middle cap and
the 56K resistor below it. Those two are coming out but
being a big fan of "don't mess with it if it ain't broke"
I might leave the other caps in unless there is an obvious
failure. Mind you, my scope works well when it does turn
on.
But I've had some other modifications it seems. What's
that square cap on the left and the 2.2K resistor doing
there? I'll have to trace the circuit to see where they
were put in and why. Maybe that was a long ago patch for
the oscillator failure? Or the cause of it now?
I see now why I had originally thought my scope was much
younger than it is - before I learned from the group here
that the "brown" Teks were pre-1954. There is this
circuit board in my scope:
http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052
Someone seems to have made factory improvements circa
1967. What was in its place before this? Is it possible
my additional HV circuit components were placed in the
same upgrades/refurbishment?
Back to the shop. I've got an hour before guests arrive!
Dan
On Saturday, December 7, 2013 10:58 AM, Don Black
wrote:
>I'm not so sure. Yours may be faulty, these are tested
good so they must be a rare animal.
>
>Don Black.
>
>On 08-Dec-13 2:31 AM, Daniel Koller wrote:
>
>
>>I'll check and see what's in there. And when I
take them out, I'll sell them on e-bay to an audiophool!!
>>http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26
>>
>>(No affiliation with the seller!)
>>
>>Dan
>>
>>On Friday, December 6, 2013 11:27 PM, Chuck Harris
wrote:
>>
>>>Most of the time with the 545, the problem is
the
black beauty oil/paper
>>>tubular capacitors used for the HV
filters. They
always go bad, and if
>>>they haven't been replaced, you must replace
them. Ceramic is fine.
>>>
>>>There is also a BB cap that is in series with
the grid
feedback winding,
>>>and another in parallel with the plate
winding. Both
must go.
>>>
>>>-Chuck Harris
>>>
>>>Daniel Koller wrote:
>>>> Howdy,
>>>>
>>>> The recent discussions on HV repairs has
me
thinking I should look into the issues
>>>> in my 545 (not A or B, old style square
case).
It works very very well, but
>>>> about half of the time, increasingly
more, the HV
circuit will not oscillate. If
>>>> I pull the plug-in out and drop it back
in, it
will work. I know this is not a
>>>> recommended option! Alternatively, if I
shut it
off and wait for it to cool, it
>>>> will work when I turn it on with about
the same
probability, or a little less.
>>>> Once the scope is on it's up to spec.
>>>>
>>>> The 6AU5 is not brand new, but is
good. It was
replaced recently with no
>>>> improvement.
>>>>
>>>> So, suggestions as to where to start on
this
intermittant problem are welcome. Is
>>>> there anything I should look for or
measure that
might indicate what is getting
>>>> tired?
>>>>
>>>> Dan
>>>>
>>>
>>>
>>>
>>>
>>
>
>
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