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Old 3rd January 2009, 06:50 PM   #1021
tlanter is offline tlanter  United States
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Default CL-30's

Chas

The manufacturers website shows the CL-30's at your C1 and C2 locations.
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Old 3rd January 2009, 07:12 PM   #1022
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I use either A1 or A2, although C1 AND C2 work as well if your transformer is <500 VA (roughly). The transformer could draw significant inrush current depending on its size and magnetization state on turn on. A1 or A2 are better positions. You could use both if the inrush is really problematic, but you'll have two CL drops.

Your D positions put the limit only on the amplifier draw, but avoids the sources of inrush current. Not sure what I think about the B spots.
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Old 3rd January 2009, 07:22 PM   #1023
AndrewT is offline AndrewT  Scotland
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A1 or A2 limit the inrush current for transformer start up.

B1 and B2 or C1 and C2 limit the charging current feeding the smoothing capacitance.

Use A2 as soft start.
Use the Bs or the Cs if you need a slow charge.
And of course you can use A2 and the Bs or A2 and the Cs for both soft start and slow charge,
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Old 3rd January 2009, 10:13 PM   #1024
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Quote:
the constantly changing current demands of a Class AB amp may not be enough to keep the thermistor hot (and therefore its resistance low).
While I'm not sure about the Class AB(I have a Class-A amp), I use the CL60 at point 'A' with good results.
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Old 4th January 2009, 07:38 AM   #1025
clm811 is offline clm811  United States
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Reviewing GE's data sheet for the thermistors :

Type Res@77degF Imax Res(Ohms)/%Imax

CL-30 2.5Ohms 8A 0.34/2A 0.14/4A 0.09/6A 0.06/8A
CL-60 10Ohms 5A 1.09/1.2A 0.44/2.5A 0.26/3.7A 0.18/5A

The CL30 requires over 2A of steady-state current to reduce the series resistance to 0.34Ohm and 4A for 0.14Ohm(I interpolate that 1A is needed for about 0.6Ohm and 3A for approx 0.2Ohm) . That's a lot of current at idle to minimize the series resistance and resultant voltage drop.

Can anyone here advise what a 10 device Leach(2 channel) amp's typical current draw might be at idle with specified bias current, 40-0-40 transformer and, say, 15- 20,000 ufd of capacitance per rail?

What are pros/cons of having a 0.2-0.5Ohm series resistance there in the power supply circuit?

Thanks for humoring a 'newbie' on a (slightly)off-topic query!

-Chas
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Old 4th January 2009, 08:35 AM   #1026
AndrewT is offline AndrewT  Scotland
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fit a delayed relay bypass across the CLx0. The delay for position A1 or A2 is about 300mS.

But for slow charge in positions B1 & B2 or C1 & C2 you require a much longer delay, maybe 5S upto 10S if the smoothing is very large.
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Old 4th January 2009, 03:49 PM   #1027
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You'll get some modulation of the PSU output with signal. Whether it is audible is an open topic. I don't think I hear mine, but I haven't tried a bypass like Andrew suggested. For the purist approach I'd say bypass it rather than leave it in.
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Old 5th January 2009, 08:22 AM   #1028
clm811 is offline clm811  United States
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Default Delay relay

Quote:
fit a delayed relay bypass across the CLx0. The delay for position A1 or A2 is about 300mS.
Can anyone here specify a relay and simple circuit that will work with minimum parts/cost?

TIA

-Chas
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Old 5th January 2009, 08:24 AM   #1029
AndrewT is offline AndrewT  Scotland
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ESP site or search here.
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Old 5th January 2009, 10:06 AM   #1030
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Chas,
I found a nice enclosed ice cube type relay on ebay with a built in variable timer for about 5 bucks -- nice quality Allen Bradley stuff. You can vary the time delay with an externally mounted resistor across the blade terminals of the relay. It is rated at 10 amps and has worked for several years on my current Leach amp. Just wire it in parallel with the CL-xx and that is it. Or you can use the normally closed contacts which will take the thermistors out of the circuit when the relay closes. It also works good with a protection circuit, but you will have to do a few mods for your particular application.
Tad
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