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Old 8th November 2012, 04:12 PM   #1
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Default Quad 22 Wiring

My Quad 22 pre-amp is feeding a David Bogen amplifier rather than the usual Quad II power amps. I have downloaded an instruction manual but what I'm after is the colour code for the cables that normally terminate with plugs 2 and 3. There are 2 brown wires which are connected to a valve (tube) base in the Bogen amp. I'm wondering if this is the heater supply?
I shipped the unit containing the 2 devices from Scotland to Hungary and it no longer works. I have tried an alternative source into the DB amp and that works so I suspect either a fault in the Quad or the wiring. I removed the DB from the main cabinet prior to shipping as it was not too secure and might have bounced around.
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Old 8th November 2012, 10:47 PM   #2
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What?
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Old 9th November 2012, 12:54 PM   #3
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Tinkelbelt,

Not sure whether this what you want.

On the Quad 22 output side there is in each output cable the screened signal wire (one white core, the other blue core). Then red and black wires, feeding the mains to each power amplifier - those branch off at the cable end to a 2-pin flat Bulgin socket on a separate lead. Then one has a blue lead in each cable, one bringing +340V d.c. to the ancillary sockets and the other for the -22 itself, from the power amplifier power supply. Finally there are two brown leads, bringing 6.3VAC to either the above ancillary sockets or the -22 itself. (The 6.3V is centre-tapped in the Quad II transformer.)

I am unfamiliar with the input configuration of the Bogen.
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Old 9th November 2012, 05:03 PM   #4
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Many thanks, Johan, that is exactly the information I needed. The mains and heater connections are OK between the Quad and the Bogen amp but I'm not sure if the HT is present.
What I have is quite unique. It started life as a late '40s RGD 746G radiogram but an ex TV engineer has modified it considerably. He fitted the Quad 22, the Bogen amp, a Quad FM tuner and a Garrard RC88 3 speed turntable to replace the original single speed item.
The Quad heater supply is coming from the Bogen but the HT (blue) wire you mentioned is going into the old RGD power supply. I assume the 340 volts can be measured with respect to the rear panel metalwork of the Quad?
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Old 9th November 2012, 08:40 PM   #5
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Yes.

The +340V is not critical. Anything from 280V upwards will not give an audible difference, but the '22 power capacitors are rated only 350V. Thus, depending, it might get an over-voltage on power-up. (That voltage later drops to about 260V through a resistor after the valves have warmed up.) Not necessarily serious, depending on whether the '22 has been refurbished with new capacitors (I hope it has - but that is another story.) Also note that there is not a separate earth/common/negative lead - that goes through the signal lead screens.
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Old 10th November 2012, 03:31 PM   #6
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I think I have found the problem! I just removed the RGD power supply chassis and realised the UU6 rectifier valve is missing. I had noted the empty valve base but just assumed the valve had been replaced by a silicon rectifier, hidden in the chassis. My memory is not good so it is quite likely that I removed the valve and put it somewhere "safe". If I can't find it, perhaps I could do such a solid state rectifier conversion? I gather that some resistors might be needed to compensate for the greater efficiency of the silicon devices?
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