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Old 8th August 2006, 12:35 AM   #1
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Default Question about BOSOZ Thermistor

I have 2 CL30s. Can these be used instead of the CL60?

Thanks,

Vince
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Old 8th August 2006, 05:28 PM   #2
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No clue, huh.
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Old 9th August 2006, 03:16 AM   #3
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I understand that CL60 has a cold resistance of 10 ohms while CL30 of 2.5 ohms. If two CL30s are applied in a series, the total cold R would be 5 Ohms, which I think useful for the inrush current control on the primary side of the transformer.
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Old 9th August 2006, 04:01 AM   #4
lgreen is offline lgreen  United States
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Hi vdi_nenna

As you know, BOSOZ has a CL-60 from ground to the 3rd prong of the AC plug, not for current inrush on the xformer primary; so I don't think that the prior post is on-topic (though its the most common use of a CL-60)

My non-expert opinion is that a CL-30 or two would be OK here. In fact you could just omit them and use a wire as many people do. I think I used one in my 1st version but not in my 2nd version....but I forget.

On other threads this is a controversial saftey issue here at diyaudio.com. Think about it, if your chassis goes "live" do you want any built in resistance from the case to the 3rd prong ground?

This is why a few of people say not to use anything from ground to 3rd prong but many others say its no big deal and helps with ground loops. Others even put in a 10-200 ohm resistor instead of a thermister. whoa. I've seen a discussion of this before but I think it would be tough to locate it with the search engine.

Perhaps the "safe" thing to do would be to omit it and use a direct connection from gnd to 3rd prong, and see if you have any hummmmm. If you do try a CL-30 in series, if still there try the other one in series.
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Old 9th August 2006, 04:55 AM   #5
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Quote:
Originally posted by lgreen

. . . not for current inrush on the xformer primary; so I don't think that the prior post is on-topic (though its the most common use of a CL-60)



Hmm . . . quite negative words.
Of course . . . i could misunderstand the question . . .

Anyhow, having the thermistor on the primary side of the bosoz is no harmful at all. I have it. Thanks to it, when I power on any one first of my pre or F1, I do not hear any "pop" noise. I am happy with the result.

If you just argue that it is no need, it would be your choice.
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Old 9th August 2006, 02:37 PM   #6
lgreen is offline lgreen  United States
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Quote:
Originally posted by Babowana

Hmm . . . quite negative words.
Of course . . . i could misunderstand the question . . .
Not intended to be negative at all. As I said the most common way of using one of these CL-60's is like you have done- inline with the primary though its not in Nelson's circuit diagram like this. Heck, I've got 2 of them there in series (with a delay circuit) to soft start mine too.

However, with all due respect, when someone asks about the cl-60 in the bosoz I take that to mean the cl-60 that appears in Nelson's bosoz schematic at the 3rd prong of the power connector.
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Old 9th August 2006, 02:55 PM   #7
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O, thanks, Lgreen.

I feel shame on me.
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Old 9th August 2006, 03:27 PM   #8
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If one CL30 will work, I'll run with it. I was worried that there would be too little resistance to ground. In other words, if the CL30 heats up too fast and the resistance drops...what will happen?

Thanks for the help.

Vince
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Old 10th August 2006, 09:22 PM   #9
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As is supposed to happen, the fuse in the primary will do it's job.

Cyclotronguy
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Old 10th August 2006, 09:40 PM   #10
steenoe is offline steenoe  Denmark
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Normally a Thermistor is not needed for a preamp! So you can safely forget about it

Steen
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