Quad II Restoration

[ginsner]

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.

[rdf]

Originally posted by ginsner
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.

[VivaVee]

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.

[planet10]

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

[VivaVee]

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 ...

[Martin Hayes]

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.

[phn]

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

[Martin Hayes]

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.

[rdf]

Originally posted by Martin Hayes
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.

[Martin Hayes]

Originally posted by rdf


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

I stand corrected. Love the glass seals at either end.