music, guitars & other obsessions

My New Curve Tracer – The XinJian QT-2

After months of debating, I finally bite the bullet and got myself a “real” curve tracer. The funny thing was, QT-2 was not even my first choice, I actually ordered the CA4810A, a relatively modern tracer that has 2V/step on its staircase generator setting, which I thought can allow me to test many small signal tubes without even a grid amplifier.

But when I got the unit, it did not function out of the box, there was no vertical deflection, so I had to return the unit! In hindsight, that was probably the best thing that could have happened, because when I opened the cover and took a peek inside, I did not like what I saw – cheap PCBs, lousy wires/wiring, cheap parts – in general a total mess… I was happy to return the unit and told the seller that I rather get something else.

After getting my refund, I went back to Taobao and start my search again, and lo and behold, there was a QT-2 available for sale right here in Shanghai, so all I had to do was to go down there and pick it up. The benefit of buying locally was that I could check out the unit in person and make sure it worked before paying for it.

But, nothing was as simple as it should – of course, the unit did not work when it was plugged at the shop, all the while the shopkeeper insisted it was working just fine when he tried it before… He spent the next hour or so, valiantly I thought to fix it, and actually found some broken Zeners and transistor on one of the power supply boards, alas, even after he replaced the components, the tracer still did not function properly. So I just had to left empty handed…another total waste of time, I thought.

A few days later, the shopkeeper called back and said “I got the tracer fixed by the factory, it is all ready for you to pick up if you still want it…” Well that was a surprise, I did not think he would bother spending money on repair it, anyway, as I later learned, he paid a factory technician to work on the unit at his home, paying probably very little for the service as they are good friends. Hey whatever to get the job done, the tracer was finally working! So I brought the curve tracer home…

This morning, I got out the tube tracer adapter and hooked it up to the curve tracer, using it simply as a test fixture for the tube. Guess what I saw – the ugly multiple traces that plagued the adapter was back! Now I don’t feel so bad about the adapter, if even factory unit with full metal chassis and proper shielding could not be immuned to the EMI, what chance did a DIY unit without a proper chassis had? [Edit: now that the tracer has a new X-Y driver board, I am no longer seeing the multiple re-traces, perhaps there is still some issues with the DIY adapter after all, will have to investigate later…]

Well all the joy lasted no more than half an hour, when the curves simply vanished without a trace 😉 while I was trying to take some screen shots, at first, I thought some fuse must have blown (as it did in the shop), but no, they were all fine, so WTF? Do I have another lemon on my hands?! When will this saga ever end! So I call the shopkeeper and told him what happened, well he said, “bring it over and let me take a another look…” So off to the shop we went again.

It took all of 3 minutes for he to figure out what was wrong – the X-Y amplifier board – which he had swap out earlier when he was trying to repair the tracer. After he put back the original board, the traces came right back, so that was it. It’s great how things sometime just sort themselves out, wish they would happen more often!

More on the QT-2 Curve Tracer, this is one of the older units on the market, but much to my surprise, I learned that it is still in production today – right here in Shanghai. I think mine dated back to the early 70’s. The construction style is “heavily influenced” by Tektronix, which makes perfect sense, since the first and extremely rare Chinese-made curve tracer, the GT-2 was an exact knockoff of the famed Tektronix 570 tube curve tracer, guess what, made by none other than XinJiang, the factory even won a national award for its achievement!

The QT-2’s design was (I am guessing) based on the Tektronix 575 but built with transistors, instead of tubes. No matter, even with transistors, this thing is a monster, and weights a whopping 50kg! There is no comparison between this unit and the CA4810A mentioned earlier, it’s like comparing Mercedes to Cherry, the difference in construction and parts selection is night and day. Yes, the CA4810 is cleaner, and built with modern parts, but it just look so un-substantial, like so many of the products that we see coming out of China these days.

The fact I paid exactly the same price for them just reinforce the saying “they don’t make them like they use to…” These old gear are worth far more, at least in my book. May be the new one works just as well, or perhaps even better, but who wants to own a POS (once you know what’s under its cover)?

The old QT-2 could use some top to bottom cleaning, the chassis is scuffed up a bit, some pots should be replaced, and it has probably not been calibrated for ages – I will do them all in good time, now I am just glad to own a piece of Chinese electronic history, plus it can trace tube curves too!

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