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Old 1st Feb 2011, 3:37 am   #1
analogadikt
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Location: Mumbai, India.
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Default Quad II OPT data and rewinding advice please.

Hallo,

I have a pair of Quad II amps that have not been used for several years, found them in the loft, where they must have been stored by my dad.

I checked these out and unfortunately have discovered that one of the OPTs is shorted between primary and secondary so needs to be repaired.
Can anybody supply me the data required to rewind this? I understand that this has a special winding that gives feedback to the cathode of the output valve. How can I get this done correctly?

Regards

analogadikt
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Old 1st Feb 2011, 3:48 pm   #2
GrimJosef
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Default Re: Quad II OPT data and rewinding advice please.

The Quad II output transformer is a sophisticated and complex item and while Quad were making the amplifiers they kept the internal details a commercial secret. Over the years several people have disassembled these transformers and have attempted to copy them, but I'm not aware that anyone has succeeded at this. There are some details of the windings on the internet (sorry, I can't remember where) but I think they are not complete.

I'm afraid your only options are i) to look out for a used transformer. This may be expensive. ii) Approach someone who has information from Quad about the transformer design and ask them for a price for a rewind. I believe Majestic Transformers http://www.transformers.uk.com/product01.htm can do this. Also Manfred Stein at Quad Musikwiedergabe http://www.quad-musik.de/, who continue to manufacture the amp to its original design, may be able to help. This could be even more expensive than a second-hand one, but do check. iii) Take your broken amplifier to pieces and sell the pieces individually on eBay. Quad spare parts fetch very high prices. Use the money you raise to buy a complete and working Quad II. If you were based in the UK, where there is a large market in Quad IIs, then I suspect this would be the cheapest option. But I'm not sure how the economics would work from Mumbai.

Cheers,

GJ
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Old 1st Feb 2011, 6:40 pm   #3
valvekits
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Default Re: Quad II OPT data and rewinding advice please.

The output transformers used to be available a few years ago from Sowter in the UK but when Quad re-introduced the Quad II in it's new format, not surprisingly, that service was withdrawn.
As Josef mentions, you can find some incomplete details on the net, for example Keith Snook's site will probably give you some idea of the difficulty involved.

http://www.keith-snook.info/QUAD-II-power-amp.html


Eddie
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Old 1st Feb 2011, 7:23 pm   #4
Trevor
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Default Re: Quad II OPT data and rewinding advice please.

After contacting quad and being quoted £235
I have rewound totally by hand a quad II output transformer I used an RS 100 watt transformer kit for the core and transformer this fitted into the quad can when finished
the turns ration from anode to cathode was 10% and the secondary was wound for 8 ohms I used 1800 turns for the anode to anode
180 for the cathode to cathode and about 90 turns for the secondary
I wound the anodes first then the spk and finally the cathode to cathode
I am a little sketchy re wire guage etc but I used a book by babanie coil winding and construction manual
regards Trev
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Old 1st Feb 2011, 8:29 pm   #5
Ed_Dinning
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Default Re: Quad II OPT data and rewinding advice please.

Hi Analogadikt, as the previous posters have said it is a complex winding, but it can be re-wound with patience.
I believe this one is potted in pitch. This is initially best removed by putting it in a freezer and then tapping gently to chip it off. (when it has been removed from the can by heat)
Identify all leads then put it in petrol so the laminations can be removed. After removing the lams put it back in petrol to loosen the rest of the pitch.
Then unwind carefully and make a lot of notes. The sequence of windings is important as is the starts and finishes and how they are linked. Replicate this and be sure to re-use the core (use a mike for wire gauges) and the results should be pretty close.
Note that some of these trannys have a small winding with 3 leads on a paxolin former, which I think is in the cathode circuit. This should be retained and re-used.

Good luck,

Ed
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Old 1st Feb 2011, 9:12 pm   #6
Trevor
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Default Re: Quad II OPT data and rewinding advice please.

I totaly agree with Ed,s comments I found such small windings but did not bother in my case I softened the pitch by putting the tx in the oven while the wife was out and using her best oven gloves to avoid being burnt!
To be honest its not that critical I feel there is a lot of hype regards these units
phasing is important or you will end up with an oscillator
I have somewhere an old practical wireless that shows such a transformer it may take a while but I will try to look it out
regards Trevor
regards
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Old 1st Feb 2011, 9:23 pm   #7
GrimJosef
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Default Re: Quad II OPT data and rewinding advice please.

Congratulations on getting the amp going Trevor ! Have you got any performance measurements ? In particular have you checked the amp for stability into difficult loads, say Quad's ESL57 speaker ?

Cheers,

GJ
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Old 1st Feb 2011, 10:05 pm   #8
Trevor
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Default Re: Quad II OPT data and rewinding advice please.

I am speaking of about 10 years ago The amplifier has since been passed on to a friend who is more into valve gear than me I really like early transistor stuff
However a few hints what I did was to use a variable voltage ac supply and injected 5 volts rms in the spk terminals and then measured the anode-anode volts the cathode to cathode volts this then gave me the ratio,s re the output transformer This is with no supply to the amplifier and all valves out
I did not do any distortion tests but on blind listening could not tell wether the amplifier with my transformer or an amplifier with the origional unit was playing opposite re which amp was right or left
1 of the strong points of the quad II was how forgiving it was re loading etc
but as ever you are playing with high voltage here about 350 if memory serves me right
Also it will suprise you if you work out as described the transformer ratio as with distributed loading it is a lot lower than you would think
regards trevor
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