Forgotten Amps.

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pre65
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#1 Forgotten Amps.

Post by pre65 »

I was talking online with a fellow enthusiast and it came up in conversation that we both had a pair of Quad 11 amps, and he was saying how nice his pair sound.

So, this morning I set out to find my pair.

Not found them yet, but I did find the KT66 SET monoblocks that were last used to drive the 833a monsters. One is dusted down and in position and the other will follow shortly.

Will I still like the sound ? Let you know later Ron.

Anyone else got long forgotten amps stashed away awaiting a listen ?

PS I will find the Quads before long. :)
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andrew Ivimey
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#2 Re: Forgotten Amps.

Post by andrew Ivimey »

I was surprised to find so many carcasses in the shed including an 'Angela' 300b stereo amp (6sj7 driver) which I dusted down, plugged in and it works.....

Depressing really.
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pre65
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#3 Re: Forgotten Amps.

Post by pre65 »

I thought you might have had an odd amp (or two :wink: ) in your shed Andrew. :)
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#4 Re: Forgotten Amps.

Post by DSJR »

My Quad II's, of which it seems I'm a lifetime custodian, were rebuilt carefully by Glenn Croft pretty faithfully believe. He did put in a twin valve regulator which drops the power output a tad but the rest doesn't look too different from original apart from better caps and resistors. The reason for the full 'Croft' rebuild was that they'd begun to falter, one of them blew panels in the 57's owned by the original keeper and Quad didn't do a thorough enough job in repairing them* - they'd have been dumped otherwise. *It's my opinion that Quad's service dept. do basic repairs only to faulty units and tend to avoid major rebuilds and restorations - maybe they've changed in recent times.

The sound is 'gloriously coloured' in all the classic ways - spacious, gentle and grain-free. Absolute magic into Epos ES14's and Quad 57's at modest volume, driven by a Croft preamp. They come out to play every so often and three of the four KT66's are original.
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pre65
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#5 Re: Forgotten Amps.

Post by pre65 »

When I find mine I may "upgrade" the KT66 cathode resistors to Arcol 50W ones fixed to the chassis. That was a Quad weak point as the original spec resistors are marginal (7W from memory)

As my pair are non original it won't affect the value. :wink:
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#6 Re: Forgotten Amps.

Post by Nick »

That was a Quad weak point as the original spec resistors are marginal (7W from memory)
If I remember they were designed to get hot, unsolder them self and fall out if a valve failed.
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pre65
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#7 Re: Forgotten Amps.

Post by pre65 »

Nick wrote: Sun Dec 03, 2017 11:59 am
That was a Quad weak point as the original spec resistors are marginal (7W from memory)
If I remember they were designed to get hot, unsolder them self and fall out if a valve failed.
I remember some Leak amps had that form of "protection". :)

On the Quad 11s the resistor eventually fails through overheating (ie insufficient dissipation).I think I have replaced them twice in 30 years.

That was the reason I first got into hi-fi forums, the week before the original WAD forum closed down.


I've now found both Quad 11s, and the special cables (phono - xlr) I made to connect them to the pre. I'll take the bases off first to check for spiders etc. :lol:
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#8 Re: Forgotten Amps.

Post by jack »

Use non-inductive Arcol resistors... just add an "N" in front of the part number.

Arcol use something called an Ayrton-Perry Winding ( http://en.wikipedia.org/wiki/Ayrton-Perry_winding ).

The reason that the maximum ohmic value is 25% of the normal range is that with, say, a 10R resistor, they divide it in 2, wind in the Ayrton-Perry style, then connect the two windings in parallel, hence 1/4 of the original value.

Arcol claim that this results in the NHSxxx components having 12% (one eighth) of the inductance of the equivalent HSxxx value.
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pre65
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#9 Re: Forgotten Amps.

Post by pre65 »

What is the benefit of lower inductance cathode resistors ?

I've just got the Quad 11s playing music.

Initial impression is very favourable. There is a bit of difference in the other equipment in the system since they were last played.
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#10 Re: Forgotten Amps.

Post by Mike H »

pre65 wrote: Sun Dec 03, 2017 12:08 pm
Nick wrote: Sun Dec 03, 2017 11:59 am
That was a Quad weak point as the original spec resistors are marginal (7W from memory)
If I remember they were designed to get hot, unsolder them self and fall out if a valve failed.
I remember some Leak amps had that form of "protection". :)

You reminded me of them wirewound resistors used to get in TV sets. Were mounted vertically, and the conductor for the top end (a metal strip) went up the side and had a solder joint halfway up, when it melted the strip would literally spring away from the body. Were ceramic encapsulated, think I've got some somewhere came from Maplin or somesuch, have got the slot in one side where the strip would go, but no metal strip included, as were axial type with normal round wires.


I problee got two or three "carcasses" of amps lying about in storage boxes, I keep threatening to get the 801A amp going again, it's supposed to be getting a SMPS based filament heater supply. Got a netbook power supply module lined up for it. The original transformer based one, plus the regulators that went with it, all got STUPIDLY hot.


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pre65
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#11 Re: Forgotten Amps.

Post by pre65 »

The heater fan resistor module on my Renault van has a similar protection facility.

In the lower speeds the module shunts through resistive coils, and if it overheats a solder joint melts and a part springs away, breaking the circuit.

Better than the Vauxhall way of setting the car on fire. :shock:
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#12 Re: Forgotten Amps.

Post by Neal »

Dug out my old 300B PP.Nice collection of dead spiders and dust inside....very surprised to see the two Ni-Cad batteries still held a charge at 1v.

Must dig out some of the other WAD amps...I recall my KiT88 wasn't very happy last time I powered it up, or the 5881 come to think about it. :shock:
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#13 Re: Forgotten Amps.

Post by Ali Tait »

Might do the same, have a pair of 300b pse tucked away.
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#14 Re: Forgotten Amps.

Post by Ant »

I went back to the el34 amp from the f5, concluded it was shite, and dismantled it.
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#15 Re: Forgotten Amps.

Post by ed »

Ant wrote: Tue Dec 05, 2017 6:46 pm I went back to the el34 amp from the f5, concluded it was shite, and dismantled it.
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