Re: A bad CRT in 465?


Eric
 

To do the high frequency compensation of the vertical what is needed is a clean square wave with a nice level top. This is for the bulk of the adjustments. The high frequency part of this needs a square wave with a fast rising edge with as square a corner as you can get (as little ringing / overshoot / undershoot as possible). The sharper the corner and the better. The bandwidth of the scope dictates the speed of the edge. In working on 485's I needed 350 Mhz this is attained with a tunnel diode pulser. But this is only good for the 1st 40ns of the wave then it Is unleveled again. The pg506 gets the 1ns rise from a -1V signal shorted to ground which gives you a "rising edge". The falling edge is a +1V fall to ground also if you are sure you can get it close Tektronix will actually still factory calibrate a 465 for $100.00 at least that is what they quoted me when I called. The 485 was $850.00 and the 7000 frames were over a grand for a factory cal. Needless to say I worked through those myself. Learned a lot too.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Timothy Freeze
Sent: Monday, April 27, 2020 1:19 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] A bad CRT in 465?

Tom,
The schematic I've seen puts five (inverters?) in parallel with with each one in series with a 220 ohm resistor. This feeds a 50 ohm load. I'm not sure but it sounds like it might work.

I fully understand your comments about inductance being critical at such a fast rise time. I'll buy the PCB available for this little project and it connects with the board directly to the scope.

I'm a little over my head, but I want to learn, so thanks for the help.

Kindest regards,
Tim

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