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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