jhoyt
Incomprehensible space llama
I got the work done (mostly) on my new Akai combo, AM-2800 and AT-2600.
First, the tuner was wrenched on: I nearly totally rebuilt the power supply, increasing the power filtering caps, and replacing a troublesome diode pair. I also replaced the caps around the output op-amp, which unfortunately is an obscure piece that I can't easily replace with a modern piece. I also added a coax connector on the back.
With the amp, I replaced all the electrolytics in the preamp section, and the input caps in the amp. Interestingly, the preamp used electrolytics all the way down to .1uF! I used Panasonic ECQ series polypropylene film caps for all sizes under 1uF, and Elna Silmic II for above. I also used Panasonic FC caps for power filtering in the preamp and power amp. Unfortunately, I forgot to order a couple cap sizes, so I will have to go back in at some point and change out the 3.3 and 33 uF caps.
When I got the amp, the right channel was blown--evidently it had been overdriven. So the power transistors in both channels were replaced with ON-Semi MJ21193/4, and some cooked resistors were replaced. Then I discovered the pre-drivers were also blown. I replaced them with a transistor pair I had on hand, a pull from a Kenwood parts unit, with very similar specs. Now, both channels have new pre-drivers also, ON-Semi TIP31C/32C.
Bias set very nicely, and I am pumped! This set is VERY nice looking, and is in great shape.
Here's what I learned:
1. Dim-bulb testers are a fuse's best friend.
2. Poly-film caps are big--and don't fit into the space of a tiny 'lytic very easily!
3. Triple-check your schematics, circuit board diagrams, and by all means look at what cap values you are removing. The schematic was going to have me put 47uF caps into the preamp signal path! What a difference a decimal point makes...
Enjoy the pics!
First, the tuner was wrenched on: I nearly totally rebuilt the power supply, increasing the power filtering caps, and replacing a troublesome diode pair. I also replaced the caps around the output op-amp, which unfortunately is an obscure piece that I can't easily replace with a modern piece. I also added a coax connector on the back.
With the amp, I replaced all the electrolytics in the preamp section, and the input caps in the amp. Interestingly, the preamp used electrolytics all the way down to .1uF! I used Panasonic ECQ series polypropylene film caps for all sizes under 1uF, and Elna Silmic II for above. I also used Panasonic FC caps for power filtering in the preamp and power amp. Unfortunately, I forgot to order a couple cap sizes, so I will have to go back in at some point and change out the 3.3 and 33 uF caps.
When I got the amp, the right channel was blown--evidently it had been overdriven. So the power transistors in both channels were replaced with ON-Semi MJ21193/4, and some cooked resistors were replaced. Then I discovered the pre-drivers were also blown. I replaced them with a transistor pair I had on hand, a pull from a Kenwood parts unit, with very similar specs. Now, both channels have new pre-drivers also, ON-Semi TIP31C/32C.
Bias set very nicely, and I am pumped! This set is VERY nice looking, and is in great shape.
Here's what I learned:
1. Dim-bulb testers are a fuse's best friend.
2. Poly-film caps are big--and don't fit into the space of a tiny 'lytic very easily!
3. Triple-check your schematics, circuit board diagrams, and by all means look at what cap values you are removing. The schematic was going to have me put 47uF caps into the preamp signal path! What a difference a decimal point makes...
Enjoy the pics!
