Re: Type 503 Oscilloscope Issues

Dave Casey

You might also take a look at the calibrator output and see if it looks
right. Just run a banana lead from the Cal Out jack on the front panel to
the vertical input. The value on the Cal Out jacks are peak to peak so the
500mV jack will give you a 1 division tall square wave when the vertical
sensitivity is set to 0.5V/cm. My 503 is not calibrated and probably out of
spec; my calibrator outputs measure closer to 400mV and 4mV, with a duty
cycle of approximately 55%. Yours may similarly not be spot on, but they
should be working and stable. The calibrator is another circuit that uses
the -100V rail so it bears checking.

Dave Casey

On Sat, May 6, 2017 at 10:55 PM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:

Going the tube removal route first, removing V484 and V474 resulted in the
-100 V bus measuring -91 V.

With the tubes back in, removing V45 caused the voltage to be -87.0 V.

Removing V135 resulted in it being - 90.0 V.

Removing V145 resulted in it being -88.6 V.

Removing V160 resulted in it being -87.8 V.

I also checked V24 and V152, since both did involve the -100 V bus at some
point in the circuit (just not directly). Removing V24 resulting in the
-100 V bus measuring -87.8 V, while removing V152 resulted in it measuring
at -85.2 V.

Again, with all of the tubes installed, the bus measures at -86.9 V.
Overall, all of the tubes had marginal effects on the -100 V bus voltage
when removed, so I will next take a look at the different adjustable
components and their effect on the measurement.

- Evan

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