Simpson 476 Mirrorscope: Success!

Finally got a trace!  Turns out that the open cathode resistor I replaced that I thought was supposed to be a 2.7k was actually supposed to be a 39k, so after rectifying that (with a 33k), and replacing the incorrect bias resistor, it lit up like a charm.


After that, I put a sine in the X & Y, and fiddled with the bias controls until I got maximum linearity.  The sweep & trigger is a little wonky, so I think I’ll run some tests with an external sweep generator to dial the amp sections in first, before I tackle the sweep.  Besides, Benton (who’s scope this is) mostly only uses X/Y mode, so that’s more important.

There is some burn-in visible on the CRT, I may poke around eBay to see if there’s a replacement that’s available and inexpensive.  The filter caps in the power supply are shockingly good, but I may replace them anyway, at least the paper ones.

After a congratulatory sip of Bourbon (4 Roses, one of my faves), I realized that all the troubles in this scope stemmed from bad 39kΩ resistors. I wonder if there was a bad batch, or they were all just under spec’d?  In any event, I’m going to replace them all, and probably up the rating to 2W, just to be sure.  I may also replace the 68k resistors that have drifted as well.

Here it is triggering on a 100kHz square wave, not bad!



2 thoughts on “Simpson 476 Mirrorscope: Success!

  1. Paul, I want to thank you for writing your blog. I stumbled across it this week and have read every post. I appreciate your excellent photography and your chronicling of the ups and downs of your restorations. I know it’s a lot of work to blog on top of doing the work. (I have my own years-inactive blog to prove it.) I hope you will share more of your repairs and restorations. Thanks!

    • Stephen – thank you so much for your kind words. I’ve learned so much of all that I know through the online communities and blogs over the years, it feels nice to contribute back to the body of knowledge, and it’s great to hear when people find it helpful or just enjoyable. It is tough to make the time, so I try not to beat myself up when I let it languish.
      I just started making my way through your own blog; you’ve made a lot of great stuff, and it’s wonderfully documented! I hope you get back to it when life allows.
      All the best,

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