Re: A possibly sick 7904A


On Wed, Aug 19, 2020 at 12:12 PM, Roger Evans wrote:

I tried putting a fast rise square wave into my 7904 at 1kHz and qualitatively
I see what you see. I have to turn up the brightness a lot to see the trace at
1ns/div and it does defocus compared with the readout. I can improve the focus
slightly and that worsens the focus of the readout significantly.

Maybe if we get some more comments we can decide who is unrealistic and who is
easily satisfied. I have no idea what the factory specifications were.
I remember my disappointment when I started collecting 'scopes in 2012/13: I fed the < 1ns rise time signal from a PG506 into my newly acquired 7904A at a fast time base setting, expecting to clearly see the wave shape. The brightness was very disappointing, even at 1 MHz repetition rate. It turned out that the CRT had seen better days and had grown a bit tired. At normal repetition rates, as encountered by the ham that had sold me this instrument, all was fine.
The 7904's and 7904A that I acquired later were much better but the limitations in writing rate were obvious.
In the analog 'scope realm, apart from the 7104 or the 2467 with their MCP CRT's, nothing beats a 7834 or 7934 analog storage 'scope in this respect: Even single-shot 1ns edge speeds can be seen clearly.


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