Re: Tektronix 475


Harvey White
 

The beam finder generally does two things:

1) unblanks the CRT by changing the bias voltage

2) changes the gain of the deflection circuits so that the maximum extent of any deflection is within the visible area of the CRT.

Some problems happen when the beam finder switch does work partially.  If, on the other hand, one plate is not being driven, I'm not sure that the beam finder would work properly.

Harvey

On 8/9/2020 7:29 AM, tenareze32@... wrote:
I have about -20 V between the first grid and the cathode, so I cannot see why the beam finder does not display at least a spot. I only saw a very faint vertical stripe with no input on the Y amp. An absence of spot or trace generally indicates an HT fault, but all HT voltages are OK.
From your explanation a running time base is required for a display, but I thought the beam finder would override that. I will check the time base circuit with another scope.
Regards
Simon


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