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Electrolytic Capacitors for Tektronix 2246A scope

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glinsky

New Member
Hi all and thanks in advance for the help. I need to replace all (12) of the low voltage power supply Electrolytic capacitors in my Tektronics 2246A due to electrolyte leakage. The scope exhibits clicking relay and lockup, but works OK sometimes. They are axial lead tall (about 2") and skinny (maybe 5/8" diameter) housings and range from 38uf to 1000 uf, and are 105 degree C rated. Many are 12 Volt. They seem to be an obsolete style. My concern is maintaining the proper (low?) ESR. Does anyone know of successful location or substitutes for these caps?
 

Hero999

Banned
I woudn't worry too much about low ESR.

The scope intermittently works now, yet the capacitors are knackered and probably have a high ESR. The new capacitors will have a much lower ESR than the existing capacitors so it's bound to work.

If they're weird values such as 38:mu:F then replace them with the nearest E6 value, i.e 10, 33, 47, 68 so for 38:mu:F use 33:mu:F although more is usually better so consider 47:mu:F.
 

Rolf

Member
Hi all and thanks in advance for the help. I need to replace all (12) of the low voltage power supply Electrolytic capacitors in my Tektronics 2246A due to electrolyte leakage. The scope exhibits clicking relay and lockup, but works OK sometimes. They are axial lead tall (about 2") and skinny (maybe 5/8" diameter) housings and range from 38uf to 1000 uf, and are 105 degree C rated. Many are 12 Volt. They seem to be an obsolete style. My concern is maintaining the proper (low?) ESR. Does anyone know of successful location or substitutes for these caps?
I would think you could get exact replacements from Tektronix but they would probably be rather expensive.
Try DigiKey they have a good supply and no minimum order restrictions. Their on line catalog is a little cumbersome to use the first time, so you have to have some time and patience.
 

Hero999

Banned
Oh, I forgot to say, low ESR is always better so if you can get lower ESR then go for it.
 

Speakerguy

Active Member
Oh, I forgot to say, low ESR is always better so if you can get lower ESR then go for it.
Unless it's on the output of an LDO regulator that needs some ESR to be stable. Then low ESR is bad :) Probably some other specific instances too, but that's the main one I can think of.
 
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Hero999

Banned
I thought of that after posting but decided not to bother editing because there's virtually no chance of it having a LDO anywhere inside.
 

Speakerguy

Active Member
True, but I've made a regulator go up in smoke before due to screwing up the cap requirements, so I thought I'd mention it (It was an 1117 regulator with very light loading). When were 2246's made?
 

glinsky

New Member
Tektronix 2246 scopes were manufactured until 1999. Mine has patent labels on certain IC's around 1994. Thanks for the warning(s). No LDO regulators inside that I can detect. I have the service manual. Also, Tek no longer provides these Caps through their parts order department. They seem to be a) larger that todays offerings, and b) rated +100% / -10% of capacitance value. Is this also an obsolete standard (no longer manufactured)?
 

Speakerguy

Active Member
Yes that seems obselete, most electrolytic caps now are rated at -20/+80%. Digikey lists some +100/-10% caps made by Cornell Dubillier, but they do not stock them.

For general applications I like the Panasonic FM and FC series capacitors. Pretty good bang for the buck, and low ESR.
 
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Hero999

Banned
I think you're worrying about this far too much, just replace the capacitors with the nearest value you can find, the lower the ESR, the better.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I think you're worrying about this far too much, just replace the capacitors with the nearest value you can find, the lower the ESR, the better.
I completely agree, just because one person had a problem on one occasion in a specific application, it doesn't mean it's a general problem.

Low-ESR capacitors aren't that much lower than normal ones, so it's extremely unlikely to make any difference.
 
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