Testing an 'unknown' Quad II - Advice please

Ian

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I bought a Quad QCII and II pair locally yesterday, a bit of a gamble as they were described as 'working last time they were used two years ago'. I went in with my eyes open, the price was very much right and I reckon I'll get my money back as parts only if they're dogs. Better than splashing it at the bookies !

The QCII is going on eBay to offset the costs of the II, which I want to keep with a view to finding another at some time. It was scruffy but an hour with Brasso and it's come up more that ok. A bonus was that on opening them up both had Quad service stickers from 2011.

So, I'm after advice on the best way to test the Quad II please. I'm thinking plugging it into my system has possible risk of damage to speakers maybe, I just wondered if this might be the case ? Many Thanks.

Screenshot 2022-06-24 075722.jpg Screenshot 2022-06-24 075747.jpg Screenshot 2022-06-24 075851.jpg Screenshot 2022-06-24 075819.jpg
 
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toprepairman

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Looks good.
The important bits (coupling caps) have been done so you should be Ok.
Power them up and keep a close eye on the KT66 anodes to make sure they don't glow red.
It won't be the caps but if the valves go gassy you get the same symptoms.
The output transformer is still set for 15 Ohms which won't suit modern speakers so you'll get reduced power and poorer bass.
 
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rabski

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Looking at the internals, and bearing in mind the service sticker, if that dropped onto the bench here, I'd glue a speaker on the blunt end and just plug it in. HOWEVER... before I did so, I'd look at the earthing. They're designed to case earth through the preamp so don't have a direct mains earth connecky. You'll need to add one as the original relies on a safety earth through the screening cable. This is officially known as 'a bad idea'.
 
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Ian

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Looking at the internals, and bearing in mind the service sticker, if that dropped onto the bench here, I'd glue a speaker on the blunt end and just plug it in. HOWEVER... before I did so, I'd look at the earthing. They're designed to case earth through the preamp so don't have a direct mains earth connecky. You'll need to add one as the original relies on a safety earth through the screening cable. This is officially known as 'a bad idea'.
Indeed, thanks Rabski, I'm tempted with this. To keep things simple I was going to go directly from my Quad CD-P.
 

rabski

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Indeed, thanks Rabski, I'm tempted with this. To keep things simple I was going to go directly from my Quad CD-P.
Only if the CD-P has a volume control old friend, of course, otherwise it'll be very loud very quickly.

Even then, I'm old school. The safety earth on the original is from the preamp, through the screen and via the Jones plug. They're hateful old things and that gives a good handful of ways in which the earth connection could be lost. I would always without fail add a safety earth. If you really want, you can do this unobtrusively and keep the original 2-pin mains connector by running a separate earth wire. Take it to one of the bolts holding the 2-pin socket and use a meter to double check. Originality notwithstanding, if it was here, the one modern modification I'd make is to drill out a little and change the 2-pin for an IEC. The original method was designed to avoid potential ground loops, but in pre to power, they're not usually a major issue.

The II was designed to sit inside a big box with the preamp and tuner visible, and the power amp hidden away. Any fault that left the power amp casing live was less of a problem that way. If you do it by connecting the CD-P, there is no guarantee there will be an earth at all. With an older valve amp, that's asking for trouble really.
 

Juancho

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Only if the CD-P has a volume control old friend, of course, otherwise it'll be very loud very quickly.

Even then, I'm old school. The safety earth on the original is from the preamp, through the screen and via the Jones plug. They're hateful old things and that gives a good handful of ways in which the earth connection could be lost. I would always without fail add a safety earth. If you really want, you can do this unobtrusively and keep the original 2-pin mains connector by running a separate earth wire. Take it to one of the bolts holding the 2-pin socket and use a meter to double check. Originality notwithstanding, if it was here, the one modern modification I'd make is to drill out a little and change the 2-pin for an IEC. The original method was designed to avoid potential

ground loops, but in pre to power, they're not usually a major issue.

The II was designed to sit inside a big box with the preamp and tuner visible, and the power amp hidden away. Any fault that left the power amp casing live was less of a problem that way. If you do it by connecting the CD-P, there is no guarantee there will be an earth at all. With an older valve amp, that's asking for trouble really.
As an alternative to drilling out and fitting an IEC socket I've fitted a small plate and a flying IEC socket with captive lead on the plate. That way you are not drilling the chassis but still providing an independent safety earth.
 
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rabski

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As an alternative to drilling out and fitting an IEC socket I've fitted a small plate and a flying IEC socket with captive lead on the plate. That way you are not drilling the chassis but still providing an independent safety earth.
Either way, and regardless of whether you go via the preamp, it really does need a direct earth connection. With a lot of single-ended preamps and CD players, the signal ground is not directly connected to chassis earth. Even where it is, it may well be via a thin wire or PCB track, so no way capable of shunting current in the event of a failure.
 
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rabski

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was heat or airflow an issue?
Doubt it. The ones I've seen are a fair size and open at the back. They were either 'raidogram' style or sat on a shelf. Compared with big triodes and the like, a Quad II doesn't chuck out excessive heat, so as long as there's a bit of room above and some airlow (from the open rear) it's unlikely to cause issues.

Mind you, apart from age-related issues like capacitors, IIRC the most common fail on IIs was mains transformers overheating and the potting compound melting.
 

nomore landings

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Great advice, rabski. My dad had a pair of 11s plus 22 pre. In later life, he told me that if anything happened to him, to disconnect from the mains before touching anything. Had had a cabinet with open back. I was very lucky to grow up listening to them - the envy of my mates.
 
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Ian

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I've ordered a pair of RCA to 6 pin Jones connectors and will be testing the QII later this week. I'll post in regard to whether my luck's in !
 

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