Quad ESL 57 Dummy load

[Bufo Bill]

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.

[snowman_al]

You will need something w a y bigger and with l o t s more heat dissipation than a Gold Flake tin...

[Bufo Bill]

Ahh, I did wonder . . . Any suggestions on containers?
Bill.

[Bufo Bill]

Thought about one of these chaps:-
https://uk.farnell.com/ohmite/tuw15j...w-5/dp/2434184
Bill.

[Bufo Bill]

And maybe a suitably sized one of these?
https://www.cricklewoodelectronics.c...90-x-51mm.html

[Radio Wrangler]

Belling lee connectors are a bit iffy for gambling an original Quad II output transformer on.

David

[Bufo Bill]

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.

[kevinaston1]

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.

[snowman_al]

Originally Posted by Bufo Bill

Thought about one of these chaps:-
https://uk.farnell.com/ohmite/tuw15j...w-5/dp/2434184
Bill.

No too small a wattage. These as a minimum https://uk.farnell.com/arcol/hs50-15...ial/dp/2678677

The diecast box idea is fine. Get the biggest you can afford.

[Bufo Bill]

Thanks very much Al.
Bill.

[Radio Wrangler]

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

[Herald1360]

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!

[Bufo Bill]

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.

[rontech]

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.

[Ted Kendall]

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.

[Herald1360]

It could be interesting applying the 15R 2uF load to some amplifiers! Funnily enough, though, the Quad II isn't bothered.

[Bufo Bill]

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.

[Radio Wrangler]

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

[Bufo Bill]

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.

[rontech]

Originally Posted by Herald1360

It could be interesting applying the 15R 2uF load to some amplifiers! Funnily enough, though, the Quad II isn't bothered.

I seem to recall that QUAD used to state that their amplifiers were unconditionally stable into any load.

Athough I never tried to prove them wrong in the days when I had their valve amps.