They do sound pretty good.
See the attached pic of their schematic.
Attachments
On a seemingly unrelated problem R201 the 1K resistor to the base of Q211 was 2K. Changed it....it was probably on its way to going totally open.
Q213 is obviously ok since the amp is working.
I did change it earlier in my repair quest, because of the rounded knee. It would be interesting to know if the original was causing a problem.
In my quest and because I had replacement transistors I also replaced the differential pair Q211 and Q212 along with Q201. I had removed them to test and I had replacements so I used them.
Also replaced Q202 and Q214 since I also removed to test and I had replacements. As it turned out Q202's collector wasn't connected.
I learned quite a bit on this repair. I did alot of head scratching because I did not expect the transistor collector not to be connected to the circuitry. The voltages and amp behavior had me going in circles.
These forums are fantastic!!
It is so beneficial to be able to have another set of eyes and brains on a problem.
Once Again a big thank you to the forum and more specifically Mooly and White Dragon!!!!
I did change it earlier in my repair quest, because of the rounded knee. It would be interesting to know if the original was causing a problem.
In my quest and because I had replacement transistors I also replaced the differential pair Q211 and Q212 along with Q201. I had removed them to test and I had replacements so I used them.
Also replaced Q202 and Q214 since I also removed to test and I had replacements. As it turned out Q202's collector wasn't connected.
I learned quite a bit on this repair. I did alot of head scratching because I did not expect the transistor collector not to be connected to the circuitry. The voltages and amp behavior had me going in circles.
These forums are fantastic!!
It is so beneficial to be able to have another set of eyes and brains on a problem.
Once Again a big thank you to the forum and more specifically Mooly and White Dragon!!!!
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Yup. Appears to be working!
Still gonna put it thru its paces....Test output power @ 200W per side.
Harmonic Distortion and Freq, Response, but I think we'll be good to go!!
Still gonna put it thru its paces....Test output power @ 200W per side.
Harmonic Distortion and Freq, Response, but I think we'll be good to go!!
Somebody had tried to repair earlier and the trace around the collector of Q202 was damaged. There was no connection between the collector and the cct. brd. Q202 collector went to nowhere
I'm very happy to report that the amp is working perfectly after putting it thru the paces.
Over 300W per side individually before clipping. I didn't test both channels simultaneously since it's rated at 200W per side.
Both channels are well within spec for harmonic distortion. Less than .1%. Measured .07%
Both channels within 1 dB on the frequency response 20Hz to 20Khz @2 watts
3.9VAC to 4.0VAC across the dummy load of 8 ohms.
I'm very happy with my purchase of this 45 year old amp.
Replaced all the electrolytic caps except the two main ones as they still tested ok.
The only caps that I replaced that tested poorly were the 10 ufd 150V ones on the input of the rails on the output boards. C206 and C219.
Amazing equipment designed back in the day.
Over 300W per side individually before clipping. I didn't test both channels simultaneously since it's rated at 200W per side.
Both channels are well within spec for harmonic distortion. Less than .1%. Measured .07%
Both channels within 1 dB on the frequency response 20Hz to 20Khz @2 watts
3.9VAC to 4.0VAC across the dummy load of 8 ohms.
I'm very happy with my purchase of this 45 year old amp.
Replaced all the electrolytic caps except the two main ones as they still tested ok.
The only caps that I replaced that tested poorly were the 10 ufd 150V ones on the input of the rails on the output boards. C206 and C219.
Amazing equipment designed back in the day.
Hi gabby. I know this is a 3 year old thread but I am working on one of these amps. Sadly I lost the install manual with clear schematics. The schemas I find online are of rather poor quality and many of the values particularly the voltages are very hard to read. do you know where I can get a better quality schematic. The problem I have is very similar to what you describe here only it is not a bad solder joint.