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Amplifier techs step in please.

T

Truck

Member
Dec 18, 2012
68
3
18
KY
Guy brought me his x200 and output is about 50 percent of what it was. I immediately thought the transistors were bad, at least one of them. I could feel that one of them was getting hot, so I thought there is my imbalance. I replaced it. No change. Replaced the other 2879, and no change. Replaced the 2290 driver and no change. What else could hurt performance by 50 percent. Thanks for any advice.
vRKG5We.jpeg
 

Does this amp have a variable knob on the front? If so, most likely that variable potentiometer has gone fault, and it's limiting your input to the 2290. Let us know if it has a variable in the front.



~Cheers~
 
It does have a variable. But that's the first thing I tried. Then I noticed the final transistors were hot.
 
for future reference a pill thats getting warm is a working pill .you want to feel for cold pills when using the touchy feely method
 
Try the capacitor across the output transformer on the 2290. Then also check the one across output transformer on the pair of 2879's. You may have to check the final capacitor near relay as well. It should be a 150pf.
 
FYI...in that type of amp, if a 2879 goes bad you have no output. If the 2290 driver goes down, there will be no output.
 
Well, I value your opinion physco, but I have to object. I've replaced several individual pills in X Force amps where output was down but not totally dead. Maybe I have misunderstood you. Please explain if I have.
 
Crusher said:
Try the capacitor across the output transformer on the 2290. Then also check the one across output transformer on the pair of 2879's. You may have to check the final capacitor near relay as well. It should be a 150pf.
Click to expand...

Crusher, I bypassed the driver pill and output fell to just under 100w pep from the 2 2879 pills. That tells me it is after the driver circuit. I lifted the ground leg of the cap right after the transformer on the 2879. I didn't have a replacement but I figured that if that cap was defective then output should have came up when I removed it from ground. It did not. The only cap is see near the relay is on the input side. I will try removing it next.
 
Crusher, It was the 150pf final cap at the relay. I wonder what would cause this to fail. I have a suspicion that the owner keyed a radio or amp into it backwards. Would this had caused it? Thanks
 
Was the capacitor a mylar, or a ceramic disc? The mylar caps are known to fail if they get close to their rated voltage. I'd recommend installing (2) 300pf 2kv ceramic disc caps in series to replace the 150pf failed cap. Putting 2 in series will give you 150pf @ 4kv. Plenty for that amp. Those will probably never fail in the lifetime of the amp. Good luck!


~Cheers~
 

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