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Classe CA-100 Soft Start Help Needed

Has anyone tried to bias this amp not knowing what they are doing? You may want to turn down the bias all the way to zero before starting it back up (after you replace the resistor). I believe some of these points are used to bypass the breaker for startup. These transformers tend to hum if bias is too high.
 
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avionic said:
Any documentation provided would be helpful. Or is this hear say? Procedure ?
Click to expand...

I know if you read the SM it talks about a soft start procedure to bypass the relays? I don’t have an amp open to look at it though. One of my CA-100 amps had a little hum coming from the transformer the first time I powered it up. Bias was way up but once I set it correct the hum went away.
 
avionic said:
Any documentation provided would be helpful. Or is this hear say? Procedure ?
Click to expand...

I am all wet here Dave, as usual! Just glanced on the SM and you have to connect on the voltage selector PCB for a soft start.
 
stoutblock said:
I am all wet here Dave, as usual! Just glanced on the SM and you have to connect on the voltage selector PCB for a soft start.
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Thanks guys! Yes, I have tools. But is def. R240 (see pic) that smoked. All four of the 4A rail fuses burned too.

I didn't think about the bias being an issue for the XFormer hum. I wish I had tried that first. I love this amp but I'm pretty gun shy now. The power config on this amp is much more complicated than on the Hafler's I've rebuilt and modded.

IMG_9426.JPG
 
I downloaded the Service Manual from HFE only to find no schematic of the input/driver stages. I'm guessing that's where R140 and R240 are. Where's the schematic?

Craig
 
R240 would be the same as R140. Whats the color code on R140? Looks like 39 something. 3.9,39,390 ?:dunno:
 
I have found you should power these up exactly like the SM says (variac etc). Also run at reduced bias for a couple of days and then balance the average of the resistors and set bias to results. Then let it run with signal and load for several days until it stabilizes.
 
stoutblock said:
I have found you should power these up exactly like the SM says (variac etc). Also run at reduced bias for a couple of days and then balance the average of the resistors and set bias to results. Then let it run with signal and load for several days until it stabilizes.
Click to expand...

Stout- Do you think the bias alone (with me turning the power of and on many times quickly) would cause the burn of R240 or is there something upstream I also need to check before replacing R240 and trying again?

Here's the SM I have...
 

Attachments

Do you have a schematic that shows R140 and R240? All of the schematics that I have found do not include the input/driver schematic, hard to troubleshoot and/or answer questions without it.

Craig
 
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