Quote:
Originally Posted by OldTechFan96
I'll start checking around IC303 and TR301 to see if anything is out of order.
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Yup, I would probably be looking for dry joints and perhaps be suspicious of those two electrolytic caps.
WME_bill thank you for joining in and you are most welcome to do so. BTW, regarding the Y amp, I rather suspect that the new input FETs may not be suitable because the input voltage at the IC is too high (about +2v vs +0.5v). Without them installed the pre-amp was balanced once the faulty transistors were replaced, and the Y plate voltages were within something like 5-6v of each other. With the JFETs installed, there was a significant differential again at the output of the pre-amp stage and through to the plates. The op swapped the IC at one point, so this seems an unlikely culprit but I am unsure. I had a similar issue with one particular scope and had to find FETs with a particularly low drain-source zero bias (IDSS) current. Any old JFET would just not do. However this was a scope with a much higher bandwidth and I'm not sure whether this is so critical for a lower bandwidth scope.