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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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27th May 2020, 5:47 pm | #1 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
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Quad ESL 57 Dummy load
I was thinking of building a dummy load for my Quad II. I have two old test records from the same era as my setup, they say to use a dummy load and measures taken with a voltmeter!
Got to look into it more, but it sounds fun doesn't it? I would enjoy building a dummy load anyway, just for something to do. Is there anything unusual to bear in mind? I was wondering about earthing in particular. I had planned to contain it in an old tobacco tin, because it looks nice. I was going to put some old Belling Lee style sockets on it. Daft I know, but fun. Cheers from Bill. |
27th May 2020, 6:41 pm | #2 |
Octode
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Re: Quad ESL 57 Dummy load
You will need something w a y bigger and with l o t s more heat dissipation than a Gold Flake tin...
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27th May 2020, 6:47 pm | #3 |
Heptode
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Re: Quad ESL 57 Dummy load
Ahh, I did wonder . . . Any suggestions on containers?
Bill. |
27th May 2020, 6:57 pm | #4 |
Heptode
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Re: Quad ESL 57 Dummy load
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27th May 2020, 7:27 pm | #5 |
Heptode
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Re: Quad ESL 57 Dummy load
And maybe a suitably sized one of these?
https://www.cricklewoodelectronics.c...90-x-51mm.html |
27th May 2020, 7:36 pm | #6 |
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Re: Quad ESL 57 Dummy load
Belling lee connectors are a bit iffy for gambling an original Quad II output transformer on.
David
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27th May 2020, 7:40 pm | #7 |
Heptode
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Re: Quad ESL 57 Dummy load
David, I'm very much learning as I go here, could you give me a little more information or maybe suggest something more suitable?
Thanks from Bill. |
27th May 2020, 7:52 pm | #8 |
Hexode
Join Date: Aug 2014
Location: Featherstone, West Yorkshire, UK.
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Re: Quad ESL 57 Dummy load
For my dummy load, I built a wooden frame about 0.2 X 0.6 X 1 metre. I calculated the length of various enamelled copper wires to give 8 ohms, and wound them accordingly (tapped for 4 and 2 ohms).
Worked fine for me for many years. The largest amplified I had was a QSC of around 2.8kW per channel, which ran for 4 hours flat out; small temperature rise of the coils, but I could hear the music as the coils rattled away. |
27th May 2020, 7:55 pm | #9 | |
Octode
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Re: Quad ESL 57 Dummy load
Quote:
The diecast box idea is fine. Get the biggest you can afford.
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27th May 2020, 8:12 pm | #10 |
Heptode
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Re: Quad ESL 57 Dummy load
Thanks very much Al.
Bill. |
27th May 2020, 9:58 pm | #11 |
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Re: Quad ESL 57 Dummy load
Belling lee connectors mate two dissimilar metals. Many aerial fitters don't even bother soldering the inner pin and rely on capacitive coupling at UHF.
Valve amplifiers do not take kindly to running off load, and even less kindly to a bad connection instantly going open for a moment. The high voltage transients can break down insulation in output transformers. Quad IIs have particularly complex output transformers with added windings for the cathodes, not just the anodes. The coupling of these at high frequencies is critical to keeping the things stable. So a bad speaker connection on a valve amp is bad, and if the transformer at risk is irreplaceable... What would I use? Something similar to what you have on the power amp would be an easy suggestion, a pair of stout binding posts would be another. Knowing the anguish an output transformer would create, I'd go for stout binding posts with a rottweiler and a machine-gun nest to keep an eye on it. David
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27th May 2020, 10:11 pm | #12 |
Dekatron
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Location: Leominster, Herefordshire, UK.
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Re: Quad ESL 57 Dummy load
Get one of these:
http://www.arcolresistors.com/resist...elled-resisto/ You can mount it on anything from a nice polished mahogany base to a tatty old chassis. Don't use it to pick up the load too soon after running it hard Though it won't get that hot with only a Quad II to tickle it!
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27th May 2020, 10:22 pm | #13 |
Heptode
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Re: Quad ESL 57 Dummy load
Hi David, thanks for your response. I think I've got my wires crossed, I'm talking about the wee belling lee banana type connections that these amps were originally fitted with. I see from a search that Belling Lee is the aerial connector, not at all what I meant sorry.
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28th May 2020, 9:28 am | #14 |
Heptode
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Re: Quad ESL 57 Dummy load
I imagine a QUAD 2 would deliver approximately 15 watts maximum. So a couple of 33 ohm 15W or 20W resistors in parallel should be OK as a 15 ohm resistive load.
However I believe an ESL 57 is a complex load with a capacitive component to its impedance. Not sure how to accommodate that in a dummy load.
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28th May 2020, 10:01 am | #15 |
Dekatron
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Re: Quad ESL 57 Dummy load
The usual formula used to be 15 ohms in parallel with 2uF, for reviewing purposes anyway, but in this case a straight resitive load is all you need.
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28th May 2020, 10:44 am | #16 |
Dekatron
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Re: Quad ESL 57 Dummy load
It could be interesting applying the 15R 2uF load to some amplifiers! Funnily enough, though, the Quad II isn't bothered.
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28th May 2020, 4:55 pm | #17 |
Heptode
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Re: Quad ESL 57 Dummy load
Guys, thank you so much for your help, you teach me more every day.
Cheers from Bill. PS The voltage calculation voltage = square root of wattage x resistance gives just over 58V, is this correct? Is this the sort of voltage a Quad ii puts out or am I totally wrong there? Cheers from Bill. Last edited by Bufo Bill; 28th May 2020 at 5:19 pm. |
28th May 2020, 7:39 pm | #18 |
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Re: Quad ESL 57 Dummy load
Watts = volts times amps
Ohms = volts/amps We can swap that last one around two ways: so amps = volts/ohms and volts = amps times ohms We can now use these in the first one and get Watts = volts times volts / ohms or Watts = amps times amps times ohms. Whichever you fancy, they are all true at once. So we can move em around again to get what we want volts times volts = watts times ohms. volts times volts is volts squared in other words. So if we get a number for volts squared and want just straight volts, we need to take the square root. Volts = square root of (watts times ohms) Note that you take the square root of the product of watts and ohms. The way some people write it without the brackets can have you rooting only one part. lessee.... 15 watts and 15 ohms gives us 225 take the square root of 225 and we get 15v RMS 21.21v peak or +/- 21.21v at the positive and negative peaks 42.42v peak-to-peak. That should cover all bases. David
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28th May 2020, 7:45 pm | #19 |
Heptode
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Re: Quad ESL 57 Dummy load
Wish i had you in algebra class! Thanks so much, it must take some time to answer my posts, I am very grateful to have your ear.
Cheers from Bill. |
28th May 2020, 8:57 pm | #20 | |
Heptode
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Re: Quad ESL 57 Dummy load
Quote:
Athough I never tried to prove them wrong in the days when I had their valve amps.
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