21-07-2020, 02:51 PM
(This post was last modified: 21-07-2020, 02:55 PM by Mike Watterson.)
The Hameg scope I have uses 485V AC on the transformer and a diode multiplier to get the approximately -2000 V EHT. There is an opto-isolator for Z-modulation as the cathode circuitry is about -1950V. The brightness uses a 62V "Zener" to drop this. I discovered this when it failed. A 741 op-amp failed at the same time.
There is curiously all the circuitry except the rear panel BNC for Z in. There is a test point on Timebase section via about 560 Ohms, so I also added a BNC on that. The rear panel is designed for three BNC connectors. I'm tempted to put a buffer to Y1 just before the chopper/invert/Alt part of the circuit so as to drive a frequency counter and/or DMM as I often want to measure frequency more accurately than counting divisions on the screen with a signal not suitable for the counter.
I'm also tempted to build a powered very low capacitance probe to look at tuned circuits without pulling them off. Some scopes have an option for this. The 10:1 probe loads too much and 100:1 probe would not be enough signal, even should it be low enough capacitance.
I have a fear of exploding electrolytics. One on a valve TV exploded putting bits of aluminium in the wall when the BY127 failed, about 1972. But even a 16V tantalum can put a glowing core across the room. Sometimes I step aside before inserting mains plug!
There is curiously all the circuitry except the rear panel BNC for Z in. There is a test point on Timebase section via about 560 Ohms, so I also added a BNC on that. The rear panel is designed for three BNC connectors. I'm tempted to put a buffer to Y1 just before the chopper/invert/Alt part of the circuit so as to drive a frequency counter and/or DMM as I often want to measure frequency more accurately than counting divisions on the screen with a signal not suitable for the counter.
I'm also tempted to build a powered very low capacitance probe to look at tuned circuits without pulling them off. Some scopes have an option for this. The 10:1 probe loads too much and 100:1 probe would not be enough signal, even should it be low enough capacitance.
I have a fear of exploding electrolytics. One on a valve TV exploded putting bits of aluminium in the wall when the BY127 failed, about 1972. But even a 16V tantalum can put a glowing core across the room. Sometimes I step aside before inserting mains plug!
