22-02-2021, 01:49 AM
Hi all,
I just found a couple of VM77Ds in my basement, and consideration of what to do with those led me to this great forum.
I bought them at an amateur radio meeting a few years ago, and thought they might be good for measuring Noise Quieting of FM receivers, but then I bought a solid-state SINADDER 3, so it never happened.
Meanwhile, when I switched them on last weekend, I was pleasantly surprised to find that that both still work. From some stickers, I know that that they came from a Technical College (probably in Sydney, Australia, where I live), and that leads me to think that they might have been very well maintained over the years. However, I can smell and hear some things happening in one of them, so I need to open them up and have a look.
After fixing obvious visible issues, I thought it might make sense to measure all the voltages marked on the circuit diagram.
Looking at the circuit of the VM77D (which does not show component values), and comparing it with those for the original VM77, VM77B and VM77C, I don't see any likely differences, except perhaps in the 150V power supply, where the neon tube (V7) seems to have been replaced by a diode as the voltage reference, which looks a bit dodgy to me!
Any helpful suggestions will be gratefully received.
Best wishes,
Lew.
Cheers,
Lew.
I just found a couple of VM77Ds in my basement, and consideration of what to do with those led me to this great forum.
I bought them at an amateur radio meeting a few years ago, and thought they might be good for measuring Noise Quieting of FM receivers, but then I bought a solid-state SINADDER 3, so it never happened.
Meanwhile, when I switched them on last weekend, I was pleasantly surprised to find that that both still work. From some stickers, I know that that they came from a Technical College (probably in Sydney, Australia, where I live), and that leads me to think that they might have been very well maintained over the years. However, I can smell and hear some things happening in one of them, so I need to open them up and have a look.
After fixing obvious visible issues, I thought it might make sense to measure all the voltages marked on the circuit diagram.
Looking at the circuit of the VM77D (which does not show component values), and comparing it with those for the original VM77, VM77B and VM77C, I don't see any likely differences, except perhaps in the 150V power supply, where the neon tube (V7) seems to have been replaced by a diode as the voltage reference, which looks a bit dodgy to me!
Any helpful suggestions will be gratefully received.
Best wishes,
Lew.
Cheers,
Lew.
