Quad II test run.

[sparkymike]

Hi GJ, swapped U and W, V now back in middle of those. Photo below of trace I am now getting with probes on first test position. (P-T and V-W)
Mike.

[Radio Wrangler]

OK, that's showing phase inversion.

David

[GrimJosef]

Can you leave the probe earth on V and move the probe tip to U, then photograph the traces PT and VU ?

Cheers,

GJ

[sparkymike]

Hi GJ, done as you posted.
Mike.

[GrimJosef]

So PT and VU are now in phase (photo in post #84) and PT and VW are out of phase (photo in post #81).

We need them the other way round - i.e. PT and VW in phase.

You said in post #81 that you'd put the connection to V back to where it always was and you'd swapped U and W. It new seems you need to swap U and W back. That should return us to the original configuration, I think. Is that right ?

But in the original configuration you photographed PT and VW out of phase (post #65). So now I'm confused.

One more quick check would be useful. Can you measure, with a multimeter, the resistance of VU, the resistance of VW and the resistance of UW. The first two should be around 16-17ohms each and the third one, UW, should be around 33ohms. (Actually since this is a rewound transformer slightly different wire gauge might have been used, so the numbers might be a bit different, but UW should still be VU + VW.)

Cheers,

GJ

[sparkymike]

Hi GJ,
V-U 22.4 ohms
V-W 22.6 ohms
U-W 44 ohms
Which is what I would have expected, so centre tap is in correct position.
The other two are reversed at the moment as per your post.
One other point, feedback wire has not been replaced yet.

Mike.

[GrimJosef]

Good that V is confirmed as the centre-tap. Well, PT and VW being in phase is correct. So once you're happy that that's the case, and PT and YZ are in phase too, then there's no need to worry about the transformer phasing any more.

Cheers,

GJ

[sparkymike]

Hi GJ,
slightly confused, do I now put U and W back on correct turret positions. (original quad position.)
Mike.

[GrimJosef]

I confess I'm confused too. You need to do whatever it takes to get the signal on PT (P grounded, T probe tip) in phase with VW (V grounded, W probe tip). V must always be the centre tap - only change U and W.

Cheers,

GJ

[sparkymike]

Will see what happens. Got to paint a wall first by order !! (I painted it once, why should I have to do it again !!)
Mike.

[sparkymike]

Photos here showing transformer connections for one of previous posters..
(I know feedback wire is not connected.)
GJ,
if I am correct, one (or more)of the following windings may have to be reversed.
Z-Y U-W X-Y or T-R.
As a matter of interest, what wave form should I get at the speaker terminals ?
Very grateful for all your help so far. I am on steep learning curve at the moment, but still learning , which is a bonus !!
Mike.

[PJL]

It might be simpler to understand if all tests used the chassis as reference so the probe earth clips can be left there. The centre taps are already AC grounded (V through R42, Y through C31).

Select Channel 1 as trigger, select chop mode, set both channels to AC.
Set the speaker link for 15 ohms.
Connect both probe earth clips to chassis.
Connect Channel 1 probe to T and measure the peak to peak voltage. Adjust this to be the top trace.
Then connect channel 2 probe to W, U, X and Z in turn recording the peak to peak voltage for each and if they are in phase or out of phase with Channel 1.

[sparkymike]

Hi PJL,
results of your test.
Channel 1 T turret. 8 volts A/C
Channel 2
W out of phase. 8 volts
U in phase 8 volts
X out of phase 74 volts
Z in phase 74 volts

Mike.

[PJL]

The phasing seems to be correct, the ratios look a little different but GJ would be best to advise.

Is this with the same connections you had with the instability, or has it been changed?

[sparkymike]

Hi PJL,
yes same connections before I started this session. Only differences is feedback wire is removed from turret and R2 & R3 (both high) have been replaced plus cap C 1
By the way, you replied to my original posting re. this amp's problem in 2006 !! Time flies when you are having fun.
Mike.

[GrimJosef]

Your ratio of YZ (74V) to VW (8V) is 9.25. My ratio for the same windings - YZ (23.18V) to VW (2.54V - corrected for very slightly different drive voltages) is 9.13. These two ratios are very close to one another and any discrepancy might well be due to small changes in mains voltage, which would cause small changes in the nominal 8V drive.

There is a difference though between your measurements and mine when it comes to the ratios of both the other winding voltages to PT's. Did you measure all these voltages by looking at the scope traces or did you use a multimeter to measure them ? If you used the scope traces then I guess PT was on one probe/channel whereas VW and YZ were on the other probe/channel. I suppose it could be that the sensitivity (Volts/cm) on one probe/channel was different from that on the other probe/channel. If you connect both probe tips to the same physical point - say to turret T - do they both read the same voltage (obviously they should) ? If not, are both the variable sensitivity knobs - the red ones in the centre of the Volts/cm knob assemblies - rotated to the CAL end ?

If you measured all the voltages with a multimeter then I'm struggling to explain why PT and VW are both reading 8V. That might be roughly true if you had the PT winding jumpered for 8ohms (Q wired to R, S wired to T). But you said you had it jumpered for 15ohms (R wired to S). Have I got that right ?

As far as the phasing goes, the results you list in post #93 show that XYZ is correctly phased to PT, but UVW has its phase reversed relative to PT. So the U and W connections need to be swapped.

Cheers,

GJ

[sparkymike]

Hi GJ,
I swopped U and W and got trace results shown at post at top of this page.
Do I revert back to that position again, which is non original position.?
Mike.

[GrimJosef]

You need to put a signal on PT and make sure that VW is in phase and YZ is in phase.

In post #93 you say W is out of phase. It needs to be in phase. If you haven't changed anything since post #93 then you need to change U and W. If you have changed them then they will now be right.

If there is any doubt about this then put a signal on PT. Check to see if VW is in phase. If it isn't in phase then swap U and W. If it is in phase then don't change anything.

Cheers,

GJ

[sparkymike]

Hi GJ,
You asked for the ohms reading for WV and VU .
These are both 23 ohms.
Mike.

[sparkymike]

I tried your last test and V W and YZ are out of phase.
Reversed U W and result the same, still out of phase.
Mike.