24 July 2011

Scope Sunday 2

It is not my intention to purchase an oscilloscope every week while I am writing this blog, but when this 547 came up on Craigslist, I couldn't help myself. The 547 is Jim's favorite scope! You can see it on his lab bench on the cover of his first book, and it's the scope used in many of the oscilloscope photos in the app notes.

It's a little dirty (OK, it's a lot dirty), but it looks like it's in pretty good shape. No physical damage and no missing tubes. It came with a Type M and a 1A4, but the seller said that one channel didn't work (probably in the Type M, since that was the one installed).

According to the seller, this one used to belong to Amar Bose, former MIT professor and founder of the Bose speaker company. (Actually, it just has a Bose property tag on it, so I think it's just Bose company surplus, and I doubt that it belonged to the big man himself... so much for a rare provenance.)

I haven't plugged it in yet. I want to clean it up a little bit first, and I'm concerned about the high-voltage transformer. The HV transformer in this scope is known to go bad. The transformer is potted in an epoxy that absorbs water and eventually fails (or causes the circuits around it to fail). Given that this scope was likely stored in a damp basement for who-knows-how long, is there a way to test the HV transformer for deterioration before just plugging it in and powering it on?

That's it. No more scopes (unless it's a 556; I still want one of those, and a 661, and a 576, and maybe another 7104... I also need a working 109 and a 7B87).


Conrad Hoffman said...

I still think about the loss of Jim most every day I'm working with analog. It was like we grew up together in different towns.

On the 547, I still use my 545 and other "boat anchors" most every day. Love 'em. Put the scope in a room with a dehumidfier and leave it for a couple weeks. My scopes have been stored and used this way for years and have avoided all HV troubles.


Kent Lundberg said...

Conrad, thanks for the comment.

Using a dehumidifier is good advice, but the HV transformer in the 547 was made with a (bad) batch of hygroscopic epoxy that eventually absorbs enough water to go bad. The 545 HV transformer is potted in beeswax, and doesn't have this problem.

There's a guy on the TekScopes Yahoo group that is/was winding new transformers for the 547 (and the other scopes plagued with this problem). I should buy one, just to be safe.