When I got this delivered I plugged it up and got nothing but the power light. So, I cracked it open and started poking around. First off I found signs of overheating on the preamp board along with a resistor that was disconnected on one side. I started taking the board loose so I could examine it better. I disconnected 4 wires. Stopped, and when I started again a week later I forgot which wires I took off from which post.... So now I am stuck. I can't even find the service manual to buy it, let alone find one to download. I'll work on that. When I got the board loose enough to flip it looked terrible. I'll definitely have to clean and re-solder it before I re-apply power to it. I didn't see any burnt traces though. Just a lot of corrosion. I am going to replace the two resistors where it looks burnt. That's all I think it might need. If any one has any schematics or knowledge of this amp I would appreciate the input.
Cheers!
Cheers!
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I don't think I am in to much trouble. I only have three wires disconnected that I need to figure out. The rest I will carefully mark and document. This will be a nice amp when I finish!
Denis, Honestly I had put this one the back burner and forgot about it. I found another one on ebay and bought it so now I have a guide to go by. The Second one I got is working but, it has a "high" , "Tinny" sound to it; Absolutely no bass or lower register whatsoever. So now I have two amps that basically do not work right. I will be diving back into them both in the coming months so I will take any advive or suggestions, and I will post my progress. Cheers!
PA systems as audio
PA amps don't or perhaps didn't always offer a full hi-fi audio range, as old shopping mall sound systems would suggest. It may still require the schematic or reverse engineering to locate any preamp filters that intentionally cut bass and high treble for announcement or background music. Otherwise, the usual treatment of replacing the electrolytic caps, main ones in particular, will restore weak sound with hum that occurs as these dry out with age and heat.
My recollection of old Realistic and similar equipment from the '70s is that that that's how they sounded, so they will be disappointing for home audio use. Mods may help but just how much, is down to the original design. As it appears to be transformer coupled to the speaker system, like most 70 or 100V line systems, there is one big limitation on bass.
PA amps don't or perhaps didn't always offer a full hi-fi audio range, as old shopping mall sound systems would suggest. It may still require the schematic or reverse engineering to locate any preamp filters that intentionally cut bass and high treble for announcement or background music. Otherwise, the usual treatment of replacing the electrolytic caps, main ones in particular, will restore weak sound with hum that occurs as these dry out with age and heat.
My recollection of old Realistic and similar equipment from the '70s is that that that's how they sounded, so they will be disappointing for home audio use. Mods may help but just how much, is down to the original design. As it appears to be transformer coupled to the speaker system, like most 70 or 100V line systems, there is one big limitation on bass.
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Thanks Ian, I was thinking along the same lines; replacing/upgrading some caps. Also I was considering replacing the output transistors. I found identical ones on ebay-- 2PCS D675 2SD675 Audio Power Transistor MOT TO-3 | eBay
But, I was hoping maybe to find a newer cross part with better performance. I will keep looking at datasheets.
But, I was hoping maybe to find a newer cross part with better performance. I will keep looking at datasheets.
try 2N3055
2N3055 STMicroelectronics | Mouser
But the Toshiba made (in red) is better than one posted on the web
2N3055 STMicroelectronics | Mouser
But the Toshiba made (in red) is better than one posted on the web
if there is also an input transformer , a similar schematic on
figure 1-29 push-pull amplifier
PUSH-PULL AMPLIFIERS
there is a missing resistor in the drawn schematics connected to R1
[bias for the two (2) transistors]
Going back to the transistor , the original is not shiny.
figure 1-29 push-pull amplifier
PUSH-PULL AMPLIFIERS
there is a missing resistor in the drawn schematics connected to R1
[bias for the two (2) transistors]
Going back to the transistor , the original is not shiny.
I also have this amplifier. It looks like 2 resistors have been overheated or perhaps cooked as the other poster had the same issue. Looks like R 207 which reads 40 ohms and R 216 which reads 170 Ohms. I wish I knew what the original values are? I cannot see and numbers or resistor band codes. I would like to replace them but their resistance may have changed since being overheated.