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Phoenix Gold XS 2500
Phoenix Gold XS 2500
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Old 27th December 2010, 02:14 AM   #1
mike49504 is offline mike49504  United States
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Join Date: Sep 2006
Default Phoenix Gold XS 2500

Replaced all the outputs in this amp. When amp is idling it idles good for 20 secs then starts drawing excessive current and the outputs heat up.

Do i need to turn the bias pots in the output section fully counter clockwise then set the bias?
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Old 27th December 2010, 03:48 AM   #2
Perry Babin is offline Perry Babin  United States
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Location: Louisiana
Were the outputs clamped tightly to the heatsink?
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Old 27th December 2010, 06:03 AM   #3
1moreamp is offline 1moreamp  United States
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Join Date: Dec 2005
Location: Northern California
Perry is correct and that you must keep these clamped to the sink due to the bias they normally operate under.

Usually when these blow outputs the circuitry in front of the outputs takes a hit also.
There will be leaky mpsa06 and 56 devices and you must verify all resistors and diodes and six of them are zeners. 6.0 X 4 and 2 X 12.0 volts respectively.
If you miss anything before the outputs being defective, when the amp gets pushed to full power it will fail the outputs again, and that is if it does not go into bias runaway just standing and idling. Look for a steady rise of current draw with no load and no signal, just idling.
They only have about $6.00 in parts in each channel, and sometimes it is necessary to rebuild it completely to get normal operations.
Gate resistors are 10 ohms.
The bias adjustment is attached to the 2sc2389 input pair and the minus 34 supply and the 339 protection circuitry 5.1 volt source. this is very unlike anything you will likely have ever seen before. It also explains the delay before the thermal runaway sets in as bias is controlled by input from the protection circuitry. Once the protection has cleared bias is allowed to commence for each channel, this is also input muting
New outputs should not mean re-cal of bias, so once you have it sinked properly you must watch for climbing current draw at idle as a sign of other damaged components. reducing channel bias will not fix climbing bias issues. it will just make it take longer before the bias runs away and smokes another set of outputs.

Last edited by 1moreamp; 27th December 2010 at 06:12 AM. Reason: Zener values
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