Hi all,

So far, I have managed to fix my old radios by probing around low voltage points .... but recently wondered about probing the Plate voltages etc.. My Scope Manual quotes max Voltage input as "400V (DC + AC Peak)" .

I have worked on the basis that this means ..... 400V Total, DC plus AC ripple and signal .... for a 1x Probe. Please correct me if this is wrong.

So what about a 10x Probe ...... Does this mean that this max input is now 4,000V Total p-p DC + AC Peak where most of the voltage will be dropped in the Probe tip?????

I know my 10x probes will handle the 1500v PP waveform on the vertical output anode of a TV - just!

I'd suggest stay under 1kv on the x10 probe and you'll be OK. With a radio that should be no problem.

Agree with Ian with radio work.
I use my CRO probes of all types set on X10, NOT X1 direct when prodding around valves.
That reduces the input voltage to the front end of a CRO.
I have never had a probe fail but when working on X1 I accidently brushed on a HV point in a radio and damaged the FET input on one of my CRO's and that was a half day job replacing the fets and the downstream chips!
Hence all the time I leave the probes set to X10.
Fred.

Thank you guys ..... I will use my 10x only Probe to avoid any silly mistakes .....

Jaycar CRO here has an input limit around 400Vp. That probably means peak to peak however, that is not as high as some of the valve ones. Its the transients that will get it. When I refitted the Ancient Heathkit OS-1 I put 2kV ones in the input to replace the 400V paper types.

Occasionally one of the CRO's here gets hooked to a plate bet its rare. In a radio its more likely to get used as a signal tracer, look at an oscillator to see if its running (it will pull it off frequency), or as an adjunct to calibrating.

I find that a signal generator & CRO make a formidable combination for finding lost signal. In calibration, apart from being more sensitive, you will see any distortion & can then use it to go find the source. 10X on plates, 1X on a transformer fed speaker and most Cathodes (not rectifier)