Re: 2N2207 replacement in 547.


fiftythreebuick <ae5i@...>
 

Glad to hear that you have jumped into the vintage Tektronix oscilloscope world! Honestly, once you get spoiled by a 500 series Tek oscilloscope, you're spoiled for good... :-)

The 547 is really a nice scope and I know you will enjoy them. I hate to tell you, but the very high probability is that your HV transformer is the source of the problem. A quick test, if you'd like to run it, is to run the scope until it fails and then hit the HV transformer with a burst of freeze spray that's sufficient to cool it significantly. If the trace returns and then fairly quickly goes away again, then it's the xfmr. The 547 is one of the known bearers of this problem.

There are a couple of folks who rewind the xfmrs, but I don't know who exactly is currently doing it. My buddy who reworked them years ago is out of it now.

I have a theory but have not tried it yet. I suspect that if the transformer is put in a vacuum chamber and held at a deep vacuum for a length of time that is sufficient to pull any moisture out of it and then sealed with something like beeswax, the transformer might be recovered. Planning to give that a try when I have time.

The worst problem with HV xfmr failure that I am aware of was with the 549 mainframe. I've worked on probably 20 or more of them and have never seen one with an original transformer that didn't have the defect. In the case of the 549s that I have, once the coil was removed and replaced with a rewound one, the problem disappeared and the scope worked as new.

Interestingly enough, the problem was extremely rare in the earlier, open frame xfmrs such as those in the Type 555 and 545A, etc.

If it turns out that you do need a xfmr, I bet someone here can point you in the right direction.

Tom

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