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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I've getting ready to start my DIY o-scope project, which would be a cheap way to get a ghetto scope. With a frequency counter it might even be pretty useful! I was originally thinking of modding a TV, like many others have. That way the CRT drive circuitry is already in place, and I just have to mod the deflection circuitry. But recently I found out that TVs use magnetic deflection, while scopes use electrostatic deflection. Is magnetic deflection too slow for a functional oscilloscope? I was hoping to use it for veiwing TC waveforms, when that time comes.
Therefore I'm wondering if I should buy a small oscilloscope tube instead, and build everything from scratch. What do you suggest?
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Why do you want to do this? - As a fun construction project: Then first get a working oscilloscope off eBay, it is going to make brewing your own much easier.
- Because you want a working oscilloscope: for gods sake, just get a cheap ghetto scope off eBay. That's proably even going to be cheaper in parts than buying a tube and all the other bits and pieces.
Re. the speed of magnetic deflection: most TVs are designed for 40Hz or so, and they do something like 200 sweeps in this time. Because TV screens are rather big, you probably want about 30 divisions instead of the usual 10. This equates to around 5us/division, I am often working at 1us/div or so around my coils, so I guess it would just about do.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
At the last swapmeet I came across 2 O-scope tubes in pretty good condition. I don't know what they were going for, but its possible to find just about anything if you look hard enough, OR find it when you're not looking for it (as in most of the time for me).
I think getting an old Heathkit 'scope would be an excellent idea. You would have all the supplies needed, the housing, and instrumentation already. This is a big bonus from a construction standpoint.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I fully agree with the idea of starting with a cheap 'scope from eBay, I have a nice Tek 'scope (broken at the moment) so I quicly bought a Scopex off eBay (20 MHz BW) I couldn't find diagrams (for free) but it's so straightforward that I can deduce the circuitry and repair it easily. My Tek on the other hand is so complex that I have problems repairing it. So a simple/cheap 'scope is an excellent starting point For TC work 10 MHz should be good. (good triggering is important to me)
The voltages (at high current) required to change the magnetic field in a TV deflection coil fast enough for a reasonable (>1 MHz) 'scope are very high, I think my attempts of many years ago resulted in about 100 kHz bandwidth (from memory), not much use other than audio. ANYONE MADE A FAST (>1 MHz BW) 'SCOPE FROM A TV/MONITOR CRT ?
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Ok, thnx for the input, it has probably saved me alot of time. I'll just hope to get lucky, although I'll never forgive myself for letting a 60 dollar scope go that one time...
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Oscilloscope tube question
