Need part for Tektronix 491 Spectrum Analyzer

I am looking for a part for a Tektronix 491 spectrum analyzer. It is called the RFI filter or the Low Pass 275 V AC Filter The Tek part number as listed in my service manual is 119-0095-00. It is a metal can that on one end has the male connector that the AC cord plugs into. The other end feeds out the line voltage to the internal fuses.

The failure is interesting. At some AC voltage around 105 - 110 volts there is a breakdown and short that blows a 20 amp circuit breaker. The short is not permanent as I can turn the unit off/on and it will again work below the above voltage. I know it is the filter as this is the only thing that is before the internal fuse which never blows.

I have a work-around by running the unit on a variac and keeping the voltage at around 100 volts. But I am not sure how long this will work, so I would like to replace the filter.

Anyone know of a source?

Please remove NOSPAM from my e-mail address if replying directly to me.

Thanks, Dave Woolf - K8RSP

Reply to
Dave Woolf
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Well, with some care, you could make one. It's a lp filter that cuts off somewhere above 60 Hz. If you don't want to build one, try to find some discarded hospital electrical equipment. They all have filters that are tested for low leakage to the chassis.



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well in the uk these are easy to find..RS FARNELL etc all stock them..they must be available in the states...

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Google search for "power input module", "emi filter", or "line filter"

Dave M

Good judgement comes from experience, and a lot of that comes from bad
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You can replace it with a stock Corcom EMI filter from Digi-Key.

This thing is a pi filter with an inductor inside and some shunt capacitors. One of the capacitors is on the way out.

Open it with a can opener and replace the ceramic caps.


"C'est un Nagra.  C'est suisse, et tres, tres precis."
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Scott Dorsey

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