Difference between a 475 and a 475A


 

I have a 475 that belonged to my father, manufactured in late 1974, that I have a sentimental attachment to and would like to keep running. To this end I have purchased several "for parts" scopes on eBay, both 475s and 475As, because many of the mechanical parts appear to be completely interchangeable. I had terrible luck with the first parts scope: while it is in terrible cosmetic condition (busted knobs, spattered with something that does not wash off with soap and water or with isopropyl alcohol), it appears to be operating flawlessly. Next I received a 475A which appears to be a much better donor candidate as it appears to be quite sick.

I have done thorough inspections of both scopes when I received them, and I noticed something odd: the sweep board of the first parts scope (475) does NOT look like the sweep board on my father's 475, but it DOES look almost identical to the sweep board on the 475A, which makes me wonder if it might not actually be a 475A with the faceplate of a 475.

I pulled down the schematics for both the 475 and the 475A and compared their vertical amplifier sections, on the basis that a higher bandwidth scope would require upgrades to the vertical amplifiers. I also made a thorough assay of the part numbers for the PCBs and custom ICs in all three scopes, hoping to find some definitive evidence for which scopes were 475s and which were 475As. Sadly, aside from the layout of the sweep board, I have not found anything conclusive.

The collected information on the three scopes follows:

475, vintage 1974
vertical amp board PN 670-224-01 or GH-2780-01
- switch IC PN 155-0091
- 1st pre-amp IC PN 155-0085-01
- 2nd pre-amp IC PN 434-0078-02 / 437-0078-02
main board PN 670-2239-04 or GE-2779-01
trigger board PN 670-2241-03 or GH-2781-01
- sweep IC PN 155-0059-01
- trigger ICs PN 155-0032-01
sweep board PN 670-2244 or GI-2784-05

475/475A? vintage 1976
vertical amp board PN 670-2240-08 or GH-2780-01
- switch IC PN 155-0091-00
- 1st pre-amp IC PN 155-0085-10
- 2nd pre-amp IC PN 019-0078-10 / 936-0078-10
main board PN 670-2239 or GE-2779-01
trigger board PN 670-2241-03 or GE-2781-02
- sweep IC PN 155-0049-02
- trigger ICs PN 155-0217-00
sweep board PN ? or GD-3980-02

475A, vintage 1978
vertical amp board PN 670-2240 or GH-2780-01
- switch IC PN 155-0091-00
- 1st pre-amp IC PN 155-0085-01
- 2nd pre-amp IC PN 813-0098-03
main board PN 670-2239 or GF-2779-01
trigger board PN 670-2241-02 or GA-2781-02
- sweep IC PN 155-0049-02
- trigger IC PN 155-0032-01
sweep board PN ? GD-3990-02

There are also differences between the parts in the 3rd pre-amp, but I'm not sure what to make of them because the physical circuit on the boards differs significantly from the schematics and parts lists.

Are the 475 and 475A really just the same scope with a marketing upgrade? I know that Tek over-engineered their scopes, and that a 475 may well be able to handle signals up to (and beyond) 250 MHz, but I expected to find noticeable upgrades to the vertical amplifiers. I suppose that it's possible that my father's scope was upgraded in the field (that is, by Tek field service personnel, not by my father), but other such modifications have been accompanied by option indicators, and there are not such indicators in my father's scope.

Have I been looking in the wrong place for the modifications that would distinguish a 475 from a 475A?

Are there, in fact, no such modifications, and the 475A was merely a marketing upgrade?

How would I be able to tell if a scope had had its front panel swapped with another scope? Is the scope serial number recorded anywhere other than on the plate at the bottom of the front panel?

Thanks,

Jeff Dutky

Join TekScopes@groups.io to automatically receive all group messages.