[GreenKeys] OT: Need help to T-Shoot this Tek 485 scope

[Bruce Phillips]

Hi drlegendre,

This link shows photo's of the boards / interconnects: 
https://sites.google.com/site/linuxdigitallab/home/tektronix-485-cathode-ray-interconnection

It looks like A15 is below A11, and vertical at the back. (see attached 
photo)

Hope that is some help.

Cheers,
Bruce







On 10/05/2017 11:15 AM, drlegendre . wrote:
> Paul,
>
> Yes, I know exactly what you're talking about and that's a very good 
> suggestion. If you have the Tek 485 manual they're 
> R1603,04,05,06,08,09. I think they use multiple parts as to avoid 
> exceeding the Emax of the resistors, which is typically around 600V. 
> One thing so far - I can find the parts on the drawing, but not on the 
> machine. Tek says they are on "transformer board A15" but no such 
> board exists, at least in the docs!
>
> But either way it's a very high-Z circuit and any kind of leakage or 
> other trouble will spoil it..
>
> Now what I +really+ need to know, is what voltage should the g1 have 
> vs. cathode? IIRC, I read -9V on g1, so at least it's proper in the 
> sense that it is negative - but what should the actual value be? And 
> what would I expect to measure with a typical (11M Zin) DVM? I mean, 
> the overall accel. potential in that tube is like 21kV (18kV anode, 
> -3kV cathode) so I'd expect to see a whole lot more than -9V bias, eh 
> - or am I way off base in my assessment?
>
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