Quad II test run.

[sparkymike]

Hi GJ,
The scope is now back in action and I am setting up again for your test details.
Now I built up a HT/LT power supply some years ago. Is there any reason why I can not use that for the LT 7 volt feed to the Quad speaker terminal. I would be happier doing that rather than connecting up to a costly Quad mains transformer
if you get my drift.
Mike.

[PJL]

GJ simply linked to the mains transformer of the amp being tested but you can also use your external supply providing it is 6.3V AC and not DC. The exercise here is to check the winding ratio and phase of the transformer windings so you just need to repeat GJ's tests and take some pics.

[sparkymike]

Hi GJ,
a few problems but I may be back in business again. I was not getting results with the Solartron scope so dug out my Advance and now with the both traces showing an ac form of sorts, with one probe on P and T and the other on V and W, if I flick the AC /DC /ground switch on both channels,to earth, one trace goes up and the other down and same when I switch back on. This Advance scope is suffering from a wide trace, (another job sometime) so not ideal.
Mike.

[sparkymike]

Bit of a brain storm in previous post. Now bringing the two traces together with X and Y controls, the two traces do not match, but peaks are together. In other words, one trace is mirror image of the other. Am I getting somewhere ? I will try and take a photo.
Mike.

[sparkymike]

Photo enclosed. I took four pics and only one was any good. Is there a certain trick to take scope photos ? I tried flash on and off. The photo here was with flash on. Would faster speed on scope when taking photo be best idea ?
Mike.

[sparkymike]

Hi GJ,
Can I take it that I now need to reverse either of the two windings, (P-T and V-W,) the V-W being easiest to get to, and then test again, If ok, then move on to the next pair or windings.
Mike.

[GrimJosef]

What signal are you using to drive the PT winding Mike ? I can (just) see the timebase knob which seems to be indicating 5 ms/cm. Is that right ? Is the Variable timebase knob - the one in the middle of the whole knob assembly - rotated round to the CAL position ?

Taking photos of scope traces is more tricky with analog scopes, like yours, than with digital scopes, like mine. On a digital scope the trace is stored and is there all the time. On an analog scope the trace sweeps across in a short time (50ms if the timebase really is 5ms/cm) and the screen then goes dark while the spot is moved back to the left hand side and the electronics wait for the next trigger to sweep it across again. If you take the photo during the dark period you will miss the trace. The only advantage of using a flash is if your room lighting is so dark that you can't see the rest of the scope in your photo. The disadvantage of using a flash is that if you point it directly at the screen it will be reflected back into the camera lens and the bright reflection could swamp the scope trace. So if you're going to use the flash then you have to photograph the screen from far enough off to one side that the flash doesn't reflect back into the camera.

Cheers,

GJ

[Radio Wrangler]

It looks like an Advance OS2100.

The bright band in the picture tells that it's in 'chop' mode, which is just what's needed for this test.

I think there's a switch to invert one channel (used to turn the channel add function into subtract) which if its active will reverse the phase of that trace, which we definitely don't want, so please check that switch.

Photos of the connections to the Quad amplifier and the scope controls will help G-J double check that your test duplicates his. It's very easy to get something swapped around on a test like this, so it's worth double checking before changing anything.

David

[GrimJosef]

I don't know the OS2000 first hand, but I take it there's nothing odd about it. I assume the bright parts of the two traces (maybe 17ms if that really is a 50Hz waveform) correspond to the beam movement when the camera shutter is open. The low-intensity parts further left on the screen are phosphorescent decay, the electron beam having passed there.

Cheers,

GJ

[Herald1360]

A tripod helps (or other means of steady support), then use a long enough exposure to get a reasonable general picture in a fairly low light level and finally adjust the trace brightness to suit. No flash and a bit of trial & error.

[Radio Wrangler]

The only thing odd about the OS2100 doesn't matter here. It uses a constant-voltage mains transformer tuned for 50Hz, so the results if anyone tries to power one from a generator can be dramatic.

The photo of the screen is good enough to show what's needed.

I lived through the period when the best you could do was a shackman or HP scope camera and a pack of polaroid film. I still think most photos I've ever taken were of CRT displays on scopes and spectrum analysers. Storage scopes were a bit thin on the ground.

David

[sparkymike]

Do I go ahead and reverse winding V-W ? There will be a time lag due to wife pressing me to get bedroom painted !! Any excuse to stop is good.
Mike.

[Radio Wrangler]

Did you check the trace invert switch isn't on?

David

[GrimJosef]

Originally Posted by sparkymike

Do I go ahead and reverse winding V-W ? There will be a time lag due to wife pressing me to get bedroom painted !! Any excuse to stop is good.
Mike.

What source were you using to drive PT? And David's question also needs answering.

Cheers,

GJ

[sparkymike]

David. Trace inverter switch was not on.
GJ I am using an old HT/LT power supply from an old valve radio.
I reversed winding V-W and now both traces match.
I went on to the your test. P-T and Y-Z and those traces match as above.
Should I power up now an see if I get decent traces and not that composite form I was getting ?
Mike.

[PJL]

It would also be a very good idea to post a picture of the underside of the amp. Also, do you know the history of the output transformer?

[sparkymike]

Photos in reply to last post.
Mike.

[PJL]

Hi Mike, can you take a picture that is vertical so that we can see the output transformer connections.

[GrimJosef]

Originally Posted by sparkymike

... I reversed winding V-W and now both traces match ...
Should I power up ... ?

It's a bit more complicated than that Mike. VW is only half the winding. The full winding is UVW with V as the centre-tap. I checked the polarity on half of it because that's easiest to do if you use the Quad's mains transformer as the AC source (it's a consequence of the way everything is earthed).

So, long story short, you need to leave V connected as it originally was (since it's the winding's centre-tap) but if you're sure about the polarities then swap U and W over.

Before powering the amp up it would be good to measure the AC voltage across PT, across VW and across YZ. The voltages should be in the same ratios as I measured.

Cheers,

GJ

[sparkymike]

Hi GJ, will do.
Voltages were in approx same ratio as yours were.