Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Solid State => Topic started by: punkykatt on September 21, 2013, 12:46:46 pm
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Hey Guys, my Bass player`s amp (Ampeg BA 115) crapped out last night at the gig. Lucky the line out was still working and coming thru the main PA so we could finish the gig. On the bench I connected head phones in the head phone jack to test and the head phone jack is working. Pulled the chassis, checked the speaker , speaker wires and connectors. All good. Checked all diodes, transistor, and resistors in the power amp section, all good. Did some voltage tests and compared to the schematic. I found that all the +40v and -40v readings to be 5.3v lower at 34.7v. The +16v and -16v a bit higher between 16.5 to 16.9v. I connected my listening amp device and I get signal all through the amp even at the speaker connectors. I rechecked the speaker wires again an tried the speaker with another amp. Would the 5.3 lower voltages in the amp cause this problem? Perhaps the electrolytic caps need replacing the PS? Any help is much appreciated. Punky
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The headphone circuit is tapped into the same point as the speaker so if it works for the headphones it should work for the speaker. However, notice that the speaker ground is switched off when you insert the headphone jack. A faulty switch (or dirty contacts) on the headphone jack would be a prime suspect.
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Sluckey, thank you, thank you, thank you.!!!!!! that was it. I cleaned up the switching ground on the head phone jack and BINGO. Fred our Bass player is going to be very pleased. So simple, a good lesson learned. Thanks again. Punky :worthy1: