Threshold 400A

johnsciolino · 28th August 2004, 01:08 AM

I just received a 400A and need some advice on what to do to keeps this thing running another 10years. I know the electrolytics need to be replaced. I read about a tantalum that can self destruct. I have about .075 of DC offset which isnt too bad.
I believe this is not adjustable. What would the bias current set at? Right now it idles at about 2-1/2 amps on the line current side and takes about 10minutes to get really warm. A previous owner informed me of a factory upgrade back in the 80's. Would this of been a circuit mod to the older units? I have the 5 fuse unit with cascode designation.

Nelson Pass · 29th August 2004, 06:50 PM

Simply replacing all the electrolytics is a good step, and none
of them are critical in value and none need more than 50 volts,
as I recall.

The bias should be set so that after the amp warms up the
heat sinks should be at a temperature where you can put your
hand on them for 5 seconds but not 10. (this, by the way, is the
standard formula I use for every amp).

28th August 2004, 01:08 AM	#1
johnsciolino diyAudio Member Join Date: Aug 2004 Location: florida	Threshold 400A I just received a 400A and need some advice on what to do to keeps this thing running another 10years. I know the electrolytics need to be replaced. I read about a tantalum that can self destruct. I have about .075 of DC offset which isnt too bad. I believe this is not adjustable. What would the bias current set at? Right now it idles at about 2-1/2 amps on the line current side and takes about 10minutes to get really warm. A previous owner informed me of a factory upgrade back in the 80's. Would this of been a circuit mod to the older units? I have the 5 fuse unit with cascode designation.

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29th August 2004, 06:50 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	Simply replacing all the electrolytics is a good step, and none of them are critical in value and none need more than 50 volts, as I recall. The bias should be set so that after the amp warms up the heat sinks should be at a temperature where you can put your hand on them for 5 seconds but not 10. (this, by the way, is the standard formula I use for every amp).