Quad II - PT autopsy begins...

[Craig Sawyers]

Primary Windings (transformers designed and made in England) PWHT02. Looking at it just now, bought for another project.

2x250V/80mA HT windings. 6.3V 2A, and 6.3V 2A centre tapped

https://primarywindings.com/product/pwht02/

They also do a PWHT01, which replaces the 6.3V winding with a 5V 2A winding for rectifier valves that are 5V heater.

Craig

[Ed_Dinning]

Just a practical note gents, make sure the lams are well butted together as sloppy air gaps between lams will send the mag current through the roof.
I once has a rewind to do on a newish mains transformer where the pri was burnt out due to poor laminating

Ed

[Ted Kendall]

Originally Posted by kalee20

Now that would be really good! It's the way towards no-compromise engineering excellence.

Horn's of Oxford made something like this in the 1960s, probably to allow customers to use Quad FM1/AM1 tuners with their new 33/303s. I had one and sold it on, but from memory it had full wave semiconductor rectification and a largish smoothing capacitor.

[dougietamson]

The laminations are in vgc, a lot of wax, for the close-up photo I cleaned the wax off.
They are type EI105 and 0.5mm thick. No idea of the type of iron, doesn't look 'barn roof' though.

[kalee20]

What's the lamination thickness?

If it's 0.35mm (a standard gauge), then I'd expect decently-spec'd material. If it's 0.5mm then it could be crummier stuff (though still adequate).

Manufacturers don't roll high-loss material thinly: reducing eddy current losses don't help much if the hysteresis losses are already high. But for low-loss material, it makes sense to reduce eddy current losses too.

It's well worth cleaning these and getting the wax off - warm oven and lots of tissue paper, then finally paraffin or white spirit while still warm.

I do have a pair of Quad II amplifiers myself - unused for at least 15 years! I'll aim to measure winding resistances, and magnetising currents on these, in the next couple of days.

[dougietamson]

Originally Posted by kalee20

What's the lamination thickness?

In my last post

Originally Posted by dougietamson

The laminations are in vgc, a lot of wax, for the close-up photo I cleaned the wax off.
They are type EI105 and 0.5mm thick. No idea of the type of iron, doesn't look 'barn roof' though.

[retailer]

0.5mm laminations are pretty much standard stuff for all of the power transformers I've rewound, the same laminations are also used in a lot of guitar amp output transformers, I have though come across a few guitar amp output transformers that use 0.35mm laminations, I've always assumed 0.35mm laminations to be grain oriented.

Run you finger along the edges of the laminations and you should feel a burr on one side, this is caused by the metal punch, once the winding is done and you're refitting the laminations make sure all the burrs face the same way, this helps to keep the laminations closer together, it's only a minuscule amount but it does make a difference, and can also help to keep laminations from buzzing.

[kalee20]

Originally Posted by dougietamson

In my last post

Oops!

As always (memo to self), read the documentation thoroughly... Thanks!

Anyway, for what it's worth. I have measured the Quad II (serial number 78943, which might help the Quad gurus to date it) mains transformer.

Using (fully calibrated) Fluke 8846A, 4-wire resistance measurements directly on the transformer tags, I get, at 22°C:

Mains winding 0 - 9.79 - 10.84 - 11.93 ohms
HT winding 68.79 - 0 - 73.11 ohms
5V winding 52.8 milliohms
6.3V winding 26.5 - 0 - 26.9 milliohms

And - for magnetising current and core loss (the latter measured with a Sangamo Weston dynamometer-type wattmeter), see the attached graph.

It does show that the turns per volt could be dropped a bit, but not a lot, with the existing laminations (which from the comments made, do seem to be general-purpose iron).

At 320V, there was a faint audible hum from the transformer, something that's not desirable of course. What isn't known is that at significantly higher flux densities, whether the transformer sprays an AC field into the KT66 right beside it.

[dougietamson]

Originally Posted by kalee20

Mains winding 0 - 9.79 - 10.84 - 11.93 ohms
HT winding 68.79 - 0 - 73.11 ohms
5V winding 52.8 milliohms
6.3V winding 26.5 - 0 - 26.9 milliohms

Thanks, good info.

[GrimJosef]

Originally Posted by kalee20

... the Quad II (serial number 78943, which might help the Quad gurus to date it) ...

I saw serial no 78963 once (or maybe just a picture of it on eBay ?) and could read the date codes on the capacitors. They were:

C1, code HDU, Wk28 1966
C2,C3, code WYU, Wk10 1966
C5, code WHU, Wk12 1966
C4/6, code XK, Oct 1966

So assuming your serial plate hasn't been transferred from another amp I'd say your amp was built either at the end of 1966 or early in 1967.

The audible hum from the transformer will likely be lessened by the bitumen potting compound. How much of any flux leakage would be shielded by the metal can I'm not sure. Maybe not much as the can's thin and LF magnetic shielding is hard work.

Cheers,

GJ

[Richardgr]

Originally Posted by dougietamson

Thanks, good info.

Isn't that what you measured in the first post? Apart from some evidence that the transformer was stressed, did you find a problem with the windings?

The chokes are known to sink in their potting compound, causing a short to earth. That would short the 5V secondary to ground. Are you sure it was Mr Peacock in the ballroom with a lead pipe that killed this transformer?

[dougietamson]

Originally Posted by Richardgr

Isn't that what you measured in the first post? Apart from some evidence that the transformer was stressed, did you find a problem with the windings?

The chokes are known to sink in their potting compound, causing a short to earth. That would short the 5V secondary to ground. Are you sure it was Mr Peacock in the ballroom with a lead pipe that killed this transformer?

It looked like reports of it demise had been greatly exaggerated as after the un-potting it came back to testing OK (the readings I posted were after un-potting)
There was a bad connection/corrosion at one of the HT leads.

Once the PT is re-wound it's on to the next component...

And then the 2nd Quad II, 22 and AM radio.

[kalee20]

Originally Posted by Richardgr

Isn't that what you measured in the first post? Apart from some evidence that the transformer was stressed, did you find a problem with the windings?

They're two different transformers!

The figures in the first post were measured by dougietamson on a faulty transformer that seemed to have 'come good' on removal from the can. The figures I gave were from one of my own amplifiers - and are very similar.

[dougietamson]

Sorry for the confusion.

The readings from Kalee20 are from his known good Quad II PT.

I measured my PT after it was removed from the bitumen, They match the known good readings and the dim bulb test was now normal.

The PT couldn't be trusted so it's being rewound.