Reed Dickinson wrote:
The ECH520 is perhaps an electrical equivalent of the ECG538 but is not amechanical equivalent. I am guessing as I cannot find any reference to a ECG520. I will give you the correct connections for a ECG538 which, I hope, will suffice for the ECG520 if the two are indeed electrical equivalents.
To use the ECG538 in a 4XX scope first remove the old 3X multiplier by removing the two nylon nuts and cutting the plastic threaded shafts off so the 3X can be removed. Position the new ECG538 such that the output cable is toward the front and drill two holes in the aluminum plate at the bottom of the shielded well. Mount the 538 using screws and hardware. Splice the old HV lead onto the new HV lead from the 538, measure the correct distance to cut twice and then cut once. Ground the D and IN leads on the 538 and connect the HV input from the scope to the LOW lead input on the 538. It may be necessary to trim metal off the cover that was over the original 3X multiplier. Do not discard the metal cover as it is a HV shield and should be in place.
Fire up and watch for a trace.
I have a 20+ year old ECG cross reference book somewhere. If I can find it, I will get the data. It seems to me that the 520 was for a B&W or 13" color TV, but I haven't replaced a tripler since the late '70s.