You're right they're both shortingWhat you have is a complementary pair class B push-pull output audio amplifier.
Usually the cause of a blown fuse is one or two bad output transistors, T7 and T8.
Unsolder both T7 and T8, making a note of where each transistor belongs.
Using an ohmmeter at the lowest resistance range, measure for conductivity between collector and emitter of the transistor with the meter leads one way and again with the leads reversed. You may find one or both of the transistors to be shorting.
With both T7 and T8 still off the board, disconnect the loudspeaker from the amplifier. Replace the fuse.
Apply power measure the +40V and -40V supply voltages at C12 and C13.
Measure the voltage at the loudspeaker output LS+ and at R5, R6, R16, R17, R19, R20.
The datasheet says up to 200khz. I'm using this to find at what frequency I can drive plasma tubes and a large air transformer at optimally.. From there can get a more specific power amp designed.. I'm open to any amp designs you know about around the 100khz 200watt range. It'll come in handy. Alternatively I'm not even sure I need 200 watts. Point was to use something like this to narrow the power requirements and frequency.Much more likely that it is to do with slow output transistors that can't switch off fast enough, leading to a shoot-through condition. Don't try that with an amplifier with a darlington output stage. A MOSFET amplifier might manage it.
Although lag-compensation (C4, C5) on the VAS in addition to dominant-pole compensation does suggest a designer struggling with a bit of instability!
Well so much for that. But yea I did notice huge drops as I increased frequency. Literally every documentation I found on this amp before buying said 3-200khz. But I'm sure it wasnt claiming full power. Can you tell what power to safely expect at 75khz from this thing?If SPICE is to believed, then it can just about manage full output at 12kHz, before it goes into slew-rate limiting.
This is its attempt at 75kHz. Note the huge DC offset due to unequal slewrates.Well so much for that. But yea I did notice huge drops as I increased frequency. Literally every documentation I found on this amp before buying said 3-200khz. But I'm sure it wasnt claiming full power. Can you tell what power to safely expect at 75khz from this thing?
The application requires a specific signal. Kind of a cut and paste waveform, but that waveform to my knowledge is only made by an arbitrary waveform generator. I guess thats definitely the easiest way.. So I have to amplify a arb signal generator.Why don't you just drive it with a squarewave, using something like a IR2153?
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by Steve Arar
by Jake Hertz
by Jake Hertz