So the other day on another forum there was an active thread about the costs of buy vs. build and amplifiers. This one I spent a bit more on than I probably should for sentimental reasons...but at the end of the day I have a beast of a 100WPC amp for under $200. It would be hard to buy transformer and case for that.
The amp is an SAE 2200, early production. Solid-state all bipolar transistor design with a pretty cool symmetric circuit design. It came not working, advertised as having new output devices.
Repairs included:
1. Replacing the fake output transistors.
2. Replace bias networks....(completely blown, previous attempt at repair were wrong values, wrong parts, installed badly, so they blew up.)
3. Replace driver transistors on one channel...one transistor had failed shorting base to collector. Oops.
4. Re-do power connection of previous repair. V- was shorting to chassis.
45 picture album SAE 2200 - Album on Imgur
Video of operation https://www.youtube.com/watch?v=otXPoGcZnNE
Scott
The amp is an SAE 2200, early production. Solid-state all bipolar transistor design with a pretty cool symmetric circuit design. It came not working, advertised as having new output devices.
Repairs included:
1. Replacing the fake output transistors.
2. Replace bias networks....(completely blown, previous attempt at repair were wrong values, wrong parts, installed badly, so they blew up.)
3. Replace driver transistors on one channel...one transistor had failed shorting base to collector. Oops.
4. Re-do power connection of previous repair. V- was shorting to chassis.
45 picture album SAE 2200 - Album on Imgur
Video of operation https://www.youtube.com/watch?v=otXPoGcZnNE
Scott
Its hard enough fixing a amplifier with the right components never mind wrong ones.
I bought an old Maplin 1980's 50 watt amplifier that was faulty.
I replaced some missing transistors with modern equivalents.
It didn't work so I checked every component on the pcb and they were fine.
All the transistors gave expected readings.
What I didn't take in to consideration was transistor p and n types.
Turned out someone had put in a pnp instead of an npn and it upset the circuit.
I couldn't read the transistors number as it was worn off so I did have half an excuse for not finding it.
I also bought in a 1980's Maplin 225WRMS amplifier with missing output transistors.
So I bought in transistors with the same number and they amplifier oscillated badly.
Turned out the new transistors had much higher gain. So I increased the VAS capacitor a bit to compensate and the amplifier worked great.
I bought an old Maplin 1980's 50 watt amplifier that was faulty.
I replaced some missing transistors with modern equivalents.
It didn't work so I checked every component on the pcb and they were fine.
All the transistors gave expected readings.
What I didn't take in to consideration was transistor p and n types.
Turned out someone had put in a pnp instead of an npn and it upset the circuit.
I couldn't read the transistors number as it was worn off so I did have half an excuse for not finding it.
I also bought in a 1980's Maplin 225WRMS amplifier with missing output transistors.
So I bought in transistors with the same number and they amplifier oscillated badly.
Turned out the new transistors had much higher gain. So I increased the VAS capacitor a bit to compensate and the amplifier worked great.
Thank you!
Hi,
Im also working on a 2200.
Your pics and video helped me immensely, thank you!
I have a couple of quick questions if your still around these forums.
Cheers
Cam
Hi,
Im also working on a 2200.
Your pics and video helped me immensely, thank you!
I have a couple of quick questions if your still around these forums.
Cheers
Cam
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