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Old 23rd Mar 2020, 4:10 pm   #1
sparkymike
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Default Quad II test run.

I want to run one of my Quad 11 amplifiers without running it through the 22 control unit.
Is that just a matter of running the mains to the Bulgin plug pins, or do I have to connect any wires in the Jones plug as well ?
Mike.
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Old 23rd Mar 2020, 6:01 pm   #2
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Default Re: Quad 11 test run

Mains to the bulgin pins yes, but if you want to feed in any signal you'll have to go via the Jones socket unless you clip straight on to the input valve grid and chassis. Remember the signal goes direct to the grid so don't use any dc offset source without a 100n cap in series with the grid side.


Don't forget to have a speaker or suitable resistor connected to the LS output as well!
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Old 23rd Mar 2020, 6:40 pm   #3
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Default Re: Quad 11 test run

Quad were very proud of their "unconditionally stable" claim. I remember some one asking advice back in the sixties in the old HiFi News magazine about running the Quad without a speaker and being told to use a dummy load - a follow up letter the next month from Quad stated that it was not required and "unconditionally stable is no idle boast".

I`d be inclined to use a resistor though.

Of course they were only 22.10 in those days.....
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Old 23rd Mar 2020, 8:35 pm   #4
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Default Re: Quad 11 test run

I'd use a load resistor too.

I'd also make sure that in the absence of the 22 I had some other RELIABLE, FAULT-CURRENT CAPABLE, mains earth connected to the II's chassis. Don't rely on the ground of the signal input lead.

It might also be handy to know that if you look at the outside of the mains chassis plug the left pin is wired to the COM terminal on the mains transformer primary and the right one is wired via the mains fuse and voltage selector to the 200/220/240V terminals. So it should be mains neutral to the left and live to the right.

Cheers,

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Old 23rd Mar 2020, 9:33 pm   #5
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Default Re: Quad 11 test run

Quote:
Originally Posted by barrymagrec View Post

Of course they were only 22.10 in those days.....
Or about 630 in today's money.

Which is still about twice what you could pick up a single Quad II for now.
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Old 23rd Mar 2020, 9:59 pm   #6
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Default Re: Quad 11 test run

Thanks for the above info.
This amplifier I built out of parts, many moons ago but is suffered from a sort of motor-boating problem which was in an earlier post of mine several years ago and which I never got to the bottom of..
Now with this enforced isolation, I thought it was high time that I had another go at the beast.I intend to go through it systematically this time and try and find out which section of the amp is causing the problem. Mind you, as soon as her who must be obeyed, senses that I have vanished into my workroom, she will no doubt dream up more mundane jobs for me !!
Mike.
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Old 24th Mar 2020, 8:55 am   #7
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Default Re: Quad 11 test run

I believe Quad called it the Quad II. So though 11 looks similar to our eyes, it'll throw search engines off the trail. One small difference for a man's eyes, one great difference for ASCII

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Old 24th Mar 2020, 9:28 am   #8
sparkymike
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Default Re: Quad 11 test run

If that is so, what do the two capital "I"s stand for ?
Impedance Impeccable ?
I have a plan of action on this amp.
I will start by removing all of the five valves. I will then check out the voltages of the mains transformer and HT and LT from that point onwards.
My intention then is to replace the rectifier and do the same checks. Next will be one of the EF86 valves, then the next etc. and checking all points, as I replace each item. After that I will probably need much advice.!!
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Old 24th Mar 2020, 9:43 am   #9
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Default Re: Quad 11 test run

Quote:
Originally Posted by sparkymike View Post
If that is so, what do the two capital "I"s stand for ?
Impedance Impeccable ?

Mike.
Roman numerals?
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Old 24th Mar 2020, 10:06 am   #10
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Default Re: Quad 11 test run

Quad II to differentiate it from the earlier model of 1951 - very similar to the II but using EF37A instead of EF86, also Octal valves in the control unit.

Quality Unit Amplifier Domestic for those not already aware.
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Old 24th Mar 2020, 10:36 am   #11
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Default Re: Quad 11 test run

Hi Mike, I built an IC pre-amp with active filter using a TL074 https://www.vintage-radio.net/forum/...d.php?t=163597 .The IC is cheap as chips (forgive the pun) and it works a treat on the Quad IIs. The chip contains 4 op amps, 2 for each channel pre-amp and 2 for eachchannel active filter. The volume setting for comfortable listening with a turntable using moving magnet pickup is about halfway to max so I know it isn't producing as much drive as the Quad22, but very useable. The Jones plugs for the AF input to the Quad II are expensive though, especially the ones adapted with a phono socket, although I suppose it depends how deep your pockets are. You can always borrow the plugs from the Quad 22 if you have one. For anyone using the circuit that I posted, note that I experienced instability using the circuit as-drawn and solved it by not using screened cables to the tone controls plus insertion of a 470R stopper resistor between the TL074 output pins and the 330nF coupling capacitor. Cheers, Jerry

Last edited by cathoderay57; 24th Mar 2020 at 10:52 am.
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Old 24th Mar 2020, 12:53 pm   #12
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Default Re: Quad 11 test run

Ok, now got some measurements. The outputs from the main transformer are LT1. 7volts / LT2. 5 volts/ and HT 675volts. I will now insert the rectifier (GZ 32) and see what I get DC volts I get there.
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Old 24th Mar 2020, 12:56 pm   #13
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Default Re: Quad 11 test run

Correct the AC /HT 656 volts.(not as above)
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Old 24th Mar 2020, 1:06 pm   #14
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Default Re: Quad 11 test run

Rectifier now in and pushing out 455 and 457volts DC
What next? Put in one of the EF86 valves , or both ?
Mike.
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Old 24th Mar 2020, 1:45 pm   #15
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Default Re: Quad 11 test run

Checked the main electrolytics. Both slightly over 16 uf.
Now I have found a problem. None of the metal skirts on the valve bases read continuity to earth. I will try a shake-proof washer under the bolt heads. Same problem on the sub chassis for the KT 66 valves. I guess this will be the same on any other metal component bolted to the chassis. Did Quad remove paint from these area to give a good earth ? I don't suppose this will have any effect on final result,who knows, but it is not correct, so must be fixed. My original Quad II reads fine on all these points.
Mike.
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Old 24th Mar 2020, 3:47 pm   #16
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Default Re: Quad 11 test run

I think they just left the metal skirts floating, so if there was a bit of muck from anode or g2 to the skirt and someone touched the skirt with the amp on, it might be a long time before their eyebrows came back round to the front.

There can be similar issues with the American metal-cased octal valves.

For a good earth contact to the skirts you'd have to get creative with a bit of the beryllium-copper spring finger stock. People have made RF UHF sockets out of this stuff for high power disc-seal triodes etc.

David
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Old 24th Mar 2020, 4:19 pm   #17
sparkymike
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Default Re: Quad 11 test run

Hi David,
all the metal points needed was a shake-proof washer under the bolt head.
My original quad had good continuity to earth on all the same points, so now this amp is the same.
I have now inserted one of the two EF86 valves and will check base voltages.
Mike.
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Old 24th Mar 2020, 4:49 pm   #18
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Default Re: Quad 11 test run

I believe you should insert both EF86s to get the biasing correct. 2.2 volts on the cathodes.
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Old 24th Mar 2020, 6:59 pm   #19
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Default Re: Quad 11 test run

Ah, I was thinking of the metal skirted bases on some generations of KT66 and KT88, not the screening can skirts on some valve holders. My mistake.

David
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Old 24th Mar 2020, 9:03 pm   #20
sparkymike
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Default Re: Quad 11 test run

My original post on this fault was in December 2006 and I have just done a search but can't locate it on the forum. From memory, I was originally getting an oscillation which was getting louder by the second. However, that does not seem to be the case now, just getting a 50 hz. mains hum. I understand that the EF 86 can suffer from hum if the valve base is not up to scratch. Maybe next thing to check. I was going to inject a signal from my sig. generator. Am I correct in saying this would be pin 2 on the jones plug ? What range should I use on the sig.gen. ?
Mike.
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