Quad 2 Concordant

[Craig Sawyers]

And in 1982 the 405 was well into cooked electrolytics, and the underrated resistors feeding the input IC zeners. So they had a few issues with ohms law and common sense in at least two of their designs.

[GrimJosef]

Is anyone honestly saying that the reason the original Quad II cathode resistor runs hot is because Peter Walker hadn't heard of Ohm's Law ? Honestly ? Hand on heart ? It was down to simple ignorance ?

I'm afraid we're running the risk of making ourselves look daft.

If we want to pick nits off probably the most successful valve amplifier in British history (it's still in production, with a single cathode resistor) then softer targets would be the Hunts capacitors, which cause the large majority of what little trouble there is in the original IIs, and the thinness of the mains transformer HT winding wire, which accounts for much of what (little) is left. Neither involves Ohm's law (which doesn't involve power, of course).

But we're going OT. If we feel that there's mud to be slung then we should start a separate thread.

Cheers,

GJ

[ahankinson]

For anyone interested in a Quad II circuit walkthrough, this one is very good, and may be helpful for the OP: https://www.youtube.com/watch?v=2rQ3llxBR6g

[Ted Kendall]

I've probably said this before, but it seems to me that if a piece of kit is known to have one or two stock faults (405 wirewounds, Revox Rifas, etc), then that is a tribute to its basic soundness of design and construction. Anything less would fail in a far more random fashion. Even Homer nods...and Walker himself reckoned that ten years was a fair life for an amplifier. We're at six times that, and counting.

[PJL]

I have a Beam Echo setup and they show up Quad kit as being built to a price. No gimmicks like potting transformers or patented features, just very solidly built version of Mullard designs like the 5-20 using good quality and safely toleranced parts. Quad did some great stuff but added more than a fair share of marketing hype.

[Ted Kendall]

Quad used ingenuity to get a quart out of a pint pot and actually sold good gear at prices people were willing to pay - for decades. Beam Echo and many others didn't. As for "For the closest approach to the original sound", that's not hype so much as a mission statement. And they walked the walk, too.

[Craig Sawyers]

Without considering the occasional "howler" (for me epitomised by the 405), by and large Quad's products have stood the test of time, and their strapline "For the closest approach to the original sound" is not a bad one.

Let's not forget the astonishment, shock and awe that the ESL57 caused when it was launched. And it is still being made by a German company who bought all Quad's jigs and fixtures. https://www.quad-musik.de/index.php/...atics/esl57-qa

And Quad's superb after sales service and spares inventory is alive and well, and still run out of Huntingdon, for which I have to doff my cap to the Chinese company that own them.

So while I may occasionally bitch and moan, I am well impressed by Quad.

[GrimJosef]

Originally Posted by PJL

I have a Beam Echo setup and they show up Quad kit as being built to a price. No gimmicks like potting transformers or patented features, just very solidly built version of Mullard designs like the 5-20 using good quality and safely toleranced parts. Quad did some great stuff but added more than a fair share of marketing hype.

We shouldn't forget that the Quad II was launched in 1953 and was based to a fair extent on its predecessor (just called the QUAD at the time) which dated back the 1940's. At the time Britain was going through a period of austerity, components were hard to come by and building to a price was the sort of approach that kept you in business.

Potting the transformers isn't really a gimmick. It costs money, so there's no point in doing it if it doesn't bring some benefits. I've just finished working on a beautiful pair of Beam Echo DL7-35s and when I'd finished with them their performance was as good as Mullard's Circuits for Audio Amplifiers said it would be. But the circuit came not out of Beam Echo but out of the hugely well-resourced Philips/Mullard company. And the amps were produced in the 1960's with the benefit of a decade's extra experience of circuit design and component improvement. Despite this Beam Echo used the same Hunts capacitors that Quad did.

Ironically the only irritation with them that I could do nothing about was a slight buzz from their mains transformers. It wasn't really loud, but given the trouble Mullard went to to silence the electronic hum through the speakers, it was a bit disappointing. Of course if Beam Echo had gone the extra mile and potted the transformers then that buzz would have been largely silenced . (I'll bet some 405 owners wish that Quad had stuck with it too.)

More generally my experience with Beam Echo has been patchy. The DL7-35s copied Mullard pretty well. But the SPA11 was an altogether more cheap and cheerful affair. Tim's (Studio263's) comments at posts #5 and #15 in this thread https://www.vintage-radio.net/forum/...d.php?t=147940 list a few issues in more detail. In mine the wiring is a bit crowded and jumbled, and everything runs pretty hot as all of the valves are inside the box with the rest of the components.

Cheers,

GJ

[onewatt]

Hi Folks,
Interesting reading, and yes I've viewed the Vintage Audio Workshop, and will view again I'm sure.

I've done a little more work and noted the following.

Powered up the tx's to see if I'm getting enough volts out albeit with diodes disconnected.
Both tx's providing 360 vac +/- 5vac & heater volts at 6.7vac not allowing for meter error.

GJ, your right! the bias is sitting at about 40v with no anode volts to circuit at this stage.

That's as much as I'm doing before reverting back to the quad II circuit. I might change the Cathode bias to independent, but I'll test my KT66's to see how they match.

I was a bit quick at reviewing the quad22 controller! Yes, it is missing valves, but, it has gained a Quad 33 pcb....More haste less speed needed!

Thank you for assistance, all much appreciated.

Chris

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