Converting a TV to an 'oscilloscope' is NOT trivial! Esp. with line-connected tv's.

What you end up with, after lots of trial & error, is something that will display a picture. This is by no means comparable to a fully functional, real oscilloscope: limited bandwidth (probably not even full audio range), bad linearity?, timebase problems, etc.etc.

Back in my student days, when money was tight, I tried building an oscilloscope from scratch. It worked, more or less... I lost interest when I was able to buy my first (2ndhand) scope for less than I had to pay in the dumpstore for just the CRT (10$, I think it was).

A few weeks later I had a second oscilloscope, als 2nd hand, for a comparable price, that just needed a bit of TLC to become fully operational. The only thing I not regret about having built my own 'oscilloscope' is that I learnt a lot about how the things work. As far a useable piece of equipment goes, I think I've made that already clear.

My advice: it's easier and cheaper to buy a 2nd hand oscilloscope, even a defect one, and try to fix that, when it's broken, than trying to convert a piece of equipment to do something that it was never intended to do. In fact, I've seen several designs in the early '90s, and decided it would be MUCH better to build a real oscilloscope from scratch, than bothering with tv's.

2nd hand oscilloscope are sold for ridiculously low prices. Yes, old tv's are usually free. In fact, when I bought my first scope, I had to haul it back home by train (being a student) together with a mate (this scope needed two people to lift :) ). The conductor was teasing me a bit about 'having to pay extra fare for that big piece of luggage' (as students, we got to travel for free anyway), and then mentioned he still had something like that at home, and if I was interested. Depended on the price of course, but after he mentioned price, I got interested. 2 weeks later, I was owner of 2 'real' scopes, plus my half-baked own design/built one.

Nowadays I use a TDS210 (LCD, very portable, 60MHz dual trace, useable up to 150MHz, very nice, LPT printer output, Fast Fourier Transform ('spectrum analysis') and I will never want to go back to using my homebuilt 'thingy'. BTW, I'm a notorious homebuilder; I don't spend money on buying equipment when I can somehow prevent it.

If you do a google search on converting a tv to oscilloscope, you should get plenty of hits.

Personally, I've once considered building the reverse: a circuit for showing tv pictures on an oscilloscope screen (like the early tv experimenters did in the '40s). Then again, why bother? There are so many much more useful projects, and I only have limited time. The gadget factor is ok though.