Hello everyone. First post here.
In the last few days I have acquired a BWD Portascope 321 made in Australia in the 1960s. It's valve driven. It still turns on and has a trace, but I have no probe.
I've been looking at a few options on aliexpress, and read a few posts here that seem to indicate pretty much any probe would be OK on an old oscilloscope provided that the bandwidth is higher (easy) and that the capacitance matches the input (not as easy).
But what I am curious about is an Active vs Passive probe, and I think I need to get this bit right.
I also have the original manual and schematic in good condition and it states this regarding input options:
1. Single ended, Impedance constant at 1M Ohm and 50pf.
2. Balanced or differential, impedance constant at 2M Ohm & 25pf.
3. Differential rejection ratio greater than 1000-1 at highest sensitivity, approx. 20-1 with attenuator in use, Subject to a maximum input of X200 atten, setting.
Then in the list of "Accessories Available" at the back of the manual:
1. High Impedance probe - Type P21 - 10M Ohm and 12 pf approx.
2. Demodulator probe - Type P10 - 200 Kc's - 100 Mc's 30V p-p
3. Screened Test prods - Type P30 - complete with prod & crocodile clips.
A few cheap probes I have looked at on aliexpress... they seem in the range but I don't know if they are active or passive and if they would be suitable for this old probe:
https://www.aliexpress.com/item/32893269108.htmlhttps://www.aliexpress.com/item/32862760535.htmlhttps://www.aliexpress.com/item/32654976903.htmlWould anyone mind giving me some advice as to what might be suitable?