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Quad II Restoration

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Quad Ii Restoration

Ok so some of you are gonna hate me but yesterday I was given a set of Quad II's with the 22 pre amp and FM tuner.
I am a lucky bastard.
anyway they are in rough shape, they have been in storage for some 20 years and by the looks of it they had been left on for long periods as one of the tranformers has leaked tar all over the top and onto the circuit board inside.
I want to restore them back to original with the only modifications being for safety concerns if they can be done without permanent changes.

So my questions are;

1. How do I safely clean off the tar without damaging the boards
2. What to look for when inspecting the tubes
3. What to do about the transformer that has leaked out all the tar

Any suggestions would be appreciated as I want to do this right.
 
Re: Quad Ii Restoration

ginsner said:
3. What to do about the transformer that has leaked out all the tar

First, I hate you. (Not really, my MC240 came the same way.) Tar to me suggests that transformer potentially experienced a violent and destructive episode. In your place I wouldn't consider powering it up without confirming that OPT has full continuity and no shorts between anything (leads, case, etc.), and ideally using a Variac to bring it up slow once you're sure it's OK.
Don't auto supply places sell a bug and tar remover for vehicle exteriors? Might be an option.
 
I 'inherited' a similar condition QuadII power amp. bASed on that experience I would say that your transformer is almost certainly well and truly fried. I cleaned the tar off mine using a small quantity of petrol in a old pot. Scrubbing with an old paint brush did the trick very nicely followed by a scrub with dishwashng detergent to get the oily petrol residue off the transformer case. I did it outside with lots of fresh air and I'm a non-smoker!

The audio output transformer case has a phenolic pcb with turrets swaged into it. These turrets allow you to change the winding ratio for different loads. The only catch with the petrol methos is that the printed labesl disappear! So write down anything you can read BEFORE ypu start cleaning. Of course, if the other unit is not damaged then you can use taht as a reference when you come to rebuild it.
 
frugal-phile™
Joined 2001
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In my experience it is usually the power transformer that fails (mine originally had 220V trafos and i ran them with a 110V>220V autoformer... Both failed almost simulataneously.

Ross Walker hand delivered me a new set of 110V replacements (which were cheap at the time) as well as gifting me with a matched quad of KT66 :)

My buddy who now has them has also had a power trafo failure (in his other set).

I do know where there should be a pair of OPTs (but they will be dear, they have been completely refurbed & cryo-treated)

dave
 
Yes, it was the power transformer that failed. I recall getting a quote for a replacement from Quad. It seemed pricey so I reverse engineered the transformer and had a local transformer manufacturer wind a replacement that would fit the original steel case. If it helps, I may be able to locate the spec used to wind them. Think, deep in the archives ...
 
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Leaking tar in Quad II amps is not unusual, and doesn't always betoken a failed power transformer. The Achilles' heel of these amps is the rating of the power traffo, which can cope – just – with the preamp and tuner drawing power. The word is that in many cases, if not most, tar has worked its way out of the housing because the power traffo has run hot, rather than because of sudden catastrophic failure.

These days Quad IIs do light duty. Seldom these days do people use the Quad preamp or tuner, opting instead for new, independently powered devices.
 
Hot mains transformer was one reason I got rid of my Leak. I never felt comfortable with it. And the Leak amps have bigger trafos than the Quad II. At least the output trafos on the smallest Leak amp, the 2x10W Stereo 20, are bigger than those of the Quad II.

I generally look at tube amps from this period as collectibles. The exceptions are the likes of the Leak TL/12. The TL/12 was basically designed for pro audio. So unless you are a collector, it might be better to fix it, sell it and build a superior amp for the money.

My :2c:
 
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I generally look at tube amps from this period as collectibles. The exceptions are the likes of the Leak TL/12. The TL/12 was basically designed for pro audio. So unless you are a collector, it might be better to fix it, sell it and build a superior amp for the money.

I'm inclined to agree. Restoring Quad IIs is a painful process for me, because I do not want to disturb their "integrity," yet it vital to replace rather a lot of components. The carbon comp resistors, which tend to drift with age, have to go, as do the Hunts-brand caps. Then there are the somewhat problematic 0.1uF coupling caps (TCC brand) on the control grids of the KT66s. These aluminium-bodied caps are clamped to the chassis, and there is, so I'm told, a pathway to ground via their bodies that is intentional and therefore forms part of the circuit. What to do? There are no modern-day equivalents.

Once you start drilling holes in the chassis and chucking out the Bulgin and Jones connectors, it's time to ask: Is it still a Quad II? The answer is no. And even if carefully and attentively restored, it will still have the characteristic roll-off at the top and bottom. Great midrange, though.
 
Martin Hayes said:
Then there are the somewhat problematic 0.1uF coupling caps (TCC brand) on the control grids of the KT66s. These aluminium-bodied caps are clamped to the chassis, and there is, so I'm told, a pathway to ground via their bodies that is intentional and therefore forms part of the circuit. What to do? There are no modern-day equivalents.

Russian K40Y-9 paper-in-oil might work. Check Ebay.
 
Restore

Well hot water did a pretty good job on the case except when It was mostly clean I found that the paint under the big deposits of tar was gone. I am guessing from the heat.
I am pretty sure this was just a case of being left on overnight or something as the tar was all over the top and onto the board below then onto the baseplate, it would have taken some time.

As far as the idea of fixing them and selling them to buy better gear goes, half the reason i love them is because of the style.
I could probably get them to a state where they could sell for a grand or more but say it takes even just 80hrs to finish and i figure my time to be worth $20/hr thats a whole lot of work for nothin.

here is a pic of what i am dealing with.
 

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Based on my experience of repairing/restoring just one power amp, I would say that this has to be a labour of love. It is not economic (and I'm a consulting electronics engineer so yr charge out rate is a bit light for me!) to do this for money. And if you are looking for a good amp it is much easier and cheaper both in terms of time and money to build a new one.

But like you, I like the retro styling. And if I squint and look at them at the right angle, I can still convince myself that the resprayed chassis full of new modern bits is still a Quad. But 'stock' or 'origonal condition'? Forget it!
 

GK

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Joined 2006
Martin Hayes said:

These aluminium-bodied caps are clamped to the chassis, and there is, so I'm told, a pathway to ground via their bodies that is intentional and therefore forms part of the circuit. What to do? There are no modern-day equivalents.


I own and work on a lot of WWII military radio transmitter / receiver stuff. Aluminium canned capacitors with their innards spewed out all over a chassis are easy to fix. Just clean them up and drill / gouge out their innards so that only a hollow can remains. Then glue inside a modern high voltage electrolytic. Do it properly and no one will know the difference :)

Cheers,
Glen
 
For info, the boxed mains capacitor is nothing but an ordinary cylindrical 2 section electrolytic capacitor encased inside with wax and the terminals wired, threaded through the turret terminals. Only recently, I dissected a pair, and replaced the old one with a new JJ 2 X 32uF electrolytic. No-one will know the difference unless by dismantling it and looking at the back.
 
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According to this Quad modification website DC Daylight, which also features the arresting X-ray pic of the amplifier, there is some voodoo about the coupling caps to the KT66 tubes and the smoothing caps in the power supply.

The website says something along these lines for the 0.1uF coupling caps:

The original capacitors had insulated metal bodies which were connected to ground. The small capacitance to ground controls the open loop frequency response and thus the stability with feedback. The capacitance to ground is about 22pF.

And says this about the CLC caps, which were originally 16uF and were paper-in-oil types, not electrolytics:

There were markings on the can that indicated each section, though having the same value, were constructed differently and had slightly different operating properties. The section closest to the rectifier was marked +P (for plain foil) and had a higher ripple rating; the section further from the rectifier was marked +E (for etched foil) and behaved more like an electrolytic.
 
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EC8010 said:
I'd say that those capacitors shown in the X-ray are about the right size and shape to be 16uF electrolytics - paper-in-oil would be much bigger.

No, I think you'll find they are indeed paper-in-oil caps. If I were restoring these amps and needed to replace these "bathtub" types, I'd go out of my way to find direct replacements. Unlike electrolytics, paper-in-oil caps are durable so NOS is okay. Besides, the four machine bolts used to secure the cap also secure the nameplate. This is part of the thoughtful economy of the design of these amps, and should be preserved.
 
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