Hi,
so I bought a 1976 vintage AM503 w/ P6303 probe. I have done similar stuff to my amp as is described here --->
https://www.circuitsathome.com/measurements/spring-cleaning. It had some extra bad caps and a heat sink was missing form 1 transistor. But after that and a whole calibration and verification procedure form the AM503 manual the amp it self runs great now. The probe I'm not so sure.
It seems that the core keeps getting a DC offset. Eg. I mesure 2 amps and it shows 2 amps. Then I turn 2 amps to 0.2 amps and it shows 0.3 - 0.4 A then I turn the current off and see that I have 0.2 amps DC offset. I then degause the probe and level it out again and its ok again. Sometimes it does this. Sometimes its ok. Sometimes after adjusting the probe (it has 4 pots - dc levelling offset and 3 frequency response & gain adjustments). It looks like even if I adjust it to where it is perfect it sometimes just goes off especially on higher sensitivity.
Is this normal, that this probes are a bit touchy feelly. Like even handling it gives it a dc offset. I know that it can pick up the earths magnetic feald and that the presune on the core and its cover (different air gap) is critical to the reading. But is this like this for all the probes? Even new ones (the multiple K euro solution). Or did my probe just see better days? I would like to have another one maybe the newer ones (only 20 years old
), like the A6303 to test them if they are the same.
If anybody has any experience with restoring these probes please give me some tips.
Best regards,
Marko