Tim Schwartz wrote in message
...
On 6/23/2010 3:48 AM, N_Cook wrote:
Just curious about these - how were they used? All that is known is they
came from an audio lab.
About 200 watt, 2.8 ohm vitreous resistors. 200watt estimated, by me,
from
surface area scaling of 2.5 and 6W ones, these are 210 mm long 35mm
diameter. Some sort of multiple series and parallel for 2 ohm etc or
with L
and C for speaker simulation ?
Nigel,
To me 2.8 ohms is an odd value. I have DALE 8 ohm 250 watt, non
inductive winding resistors. With four of them, I have 8 ohms at 250
watts, or 4 ohms at 500 watts. If I had felt the need I could have done
some more complicated switching and also had 16 ohms at 500 watts.
They are very useful as you can hook them up as a dummy load and view
on your scope, and run rather large amp right up to clipping, all while
not having to listen to any of it. It also makes it easy to measure
power at clipping, as long as you also monitor your mains voltage. (At
clipping, you have to watch the voltage drop at your bench outlet, as
you might be feeding the amp a lower mains voltage than it is specified
for, which will reduce power output. I have a VARIAC to correct for
this.)
I have seen one manufactured unit that used 7.87 ohm resistors, as they
figured out the resistance of the wiring and switching. I put together
my own, and did not feel the need for that level of accuracy.
The loads that I have are resistive, so not as difficult to drive as a
speaker might be, but again, good enough for my needs.
You did not specify the make or model of the resistors, or how they
were wired up.
Regards,
Tim Schwartz
Bristol Electronics
Marked neatly on the curve 2R8 +/-5 % and then 87.31 perhaps 31/52 of 1987.
I picked up the last 3 at a hamfest on Sunday, I did not think to ask how
many he had originally.
I'd not googled the Arcol name stamped on the brackets as they did not look
original to the resistor section, thinking it was just a maker of steel
brackets.
Crinkle form type at top of this image
http://www.arcolresistors.com/images...tubular-family.
jpg
but still leaves mystery of 2R8