Craig, I remember repairing Marantz receivers where the speaker protection relay would arch when the and burn up. It was caused by a diode in the bias circuit that was intermittent and caused the dc to slam to the minus or plus rail. When the relay opened, it provided a short to the speaker and a good path to ground for the arch.
Thanks for the clamp down boards, they are very nice. I am also glad you posted a picture of the pl14 board. I would have gotten Q1 and 2 reversed had I not taken a close look. A couple tips: Change out C6 with a 470 1W capacitor for better, deeper, bass response. Also, bridge the legs of C6 with 2 IN4148 diodes, in opposite direction to each other. This is known as the Geppeto mod, and helps prevent latchup and oscillation. Joe of White Oak Audio can explain the technical aspects of this mod. Once again, thanks for the great video.
Excellent presentation. I rebuilt a Dynaco Stereo 400 last year, and it was a very satisfying project. Your ability to design and add PCB for upgrades is impressive.
I bought a used one sometime ago that was dead, I changed out the fuses because they were blown but I have not even powered it up lol.... I guess haven't really been curious about whether it works or not until now.
If the speaker fuses were blown.. don't bother testing it. You've got something shorted somewhere. I find most often it's a pre-driver failure. It won't always cook the output devices, BUT I recommend you check every transistor on the main board, and all of the outputs. The first TO-3 output transistors (RCA 410's) are drivers for the main outputs. Those usually don't go bad. If it's just the main fuse that went bad, it may have been inrush current trying to reform the old filter caps. Bring it up slowly on a variac or use a dim bulb to limit current. You'll likely need new filter caps. Easy to do and easily available.
Dear Sir, I would like to ask a question about your protection circuit. What is the electrical current specification for the 1.75uH inductor? Or if you made it yourself, what is the AWG, number of turns, and diameter? I would be very grateful if you allow me to use your design to add to my amplifier. Thank you very much.
Fantastic! I admire your approach of attempting to maintain the original design with tasteful enhancements. When and where can we buy the pcb’s you built and incorporated!?!?!? Thanks again for sharing 👍
Great video. I'd be interested if you would be selling the unpopulated protection board. I'm restoring 2 PL400's, and really like your design. Thanks Richard
Yes they did, and they are a bit more popular and command more money . I have a 700b myself that I am doing all the white oak and a few other upgrades .
Craig, I remember repairing Marantz receivers where the speaker protection relay would arch when the and burn up. It was caused by a diode in the bias circuit that was intermittent and caused the dc to slam to the minus or plus rail. When the relay opened, it provided a short to the speaker and a good path to ground for the arch.
Thanks for the clamp down boards, they are very nice. I am also glad you posted a picture of the pl14 board. I would have gotten Q1 and 2 reversed had I not taken a close look. A couple tips: Change out C6 with a 470 1W capacitor for better, deeper, bass response. Also, bridge the legs of C6 with 2 IN4148 diodes, in opposite direction to each other. This is known as the Geppeto mod, and helps prevent latchup and oscillation. Joe of White Oak Audio can explain the technical aspects of this mod. Once again, thanks for the great video.
Excellent presentation. I rebuilt a Dynaco Stereo 400 last year, and it was a very satisfying project. Your ability to design and add PCB for upgrades is impressive.
Yea, It was a fun project.
really like the format of this video. No fluff, all business. thank you.
I have an old SAE I would like to have it put back online. I really miss listening to it.
I bought a used one sometime ago that was dead, I changed out the fuses because they were blown but I have not even powered it up lol.... I guess haven't really been curious about whether it works or not until now.
If the speaker fuses were blown.. don't bother testing it. You've got something shorted somewhere. I find most often it's a pre-driver failure. It won't always cook the output devices, BUT I recommend you check every transistor on the main board, and all of the outputs. The first TO-3 output transistors (RCA 410's) are drivers for the main outputs. Those usually don't go bad. If it's just the main fuse that went bad, it may have been inrush current trying to reform the old filter caps. Bring it up slowly on a variac or use a dim bulb to limit current. You'll likely need new filter caps. Easy to do and easily available.
Hi from Belgium ! Good job !! Did you adjust the bias on the control board ? Do you sell protection board for speakers ?? thank you.
I show bias check at 20.23 into the video. Offset was around .3 volts. I have a couple unpopulated protection boards left.
Dear Sir, I would like to ask a question about your protection circuit. What is the electrical current specification for the 1.75uH inductor? Or if you made it yourself, what is the AWG, number of turns, and diameter? I would be very grateful if you allow me to use your design to add to my amplifier. Thank you very much.
It's 10 turns #14 enamel wound on 3/4 dia PVC pipe as a form.
Fantastic! I admire your approach of attempting to maintain the original design with tasteful enhancements. When and where can we buy the pcb’s you built and incorporated!?!?!? Thanks again for sharing 👍
I may have a couple extra blank PCB's around here. You would need the ability to solder SMD parts.
Great video. I'd be interested if you would be selling the unpopulated protection board. I'm restoring 2 PL400's, and really like your design. Thanks Richard
I'll check an see how many boards I have left.
@@CIRCUITDESIGNER thanks!
@@Sunnbobb I have 4 boards available.
@@CIRCUITDESIGNER Thanks, I sent an email.
just curious to know why you felt you had to give the LED's DC, they would work just as well with AC
Too dim with AC. They only glow during half the cycle.
Cant remember, but i seem to think that they made a 700 as well.
Yes they did !
Yes they did, and they are a bit more popular and command more money . I have a 700b myself that I am doing all the white oak and a few other upgrades .
Wow...this amp brought back memories as I had it back in the day,
beautiful work!
Very nice !
#00000110110 #true400RMS..
#0001110000001.
#power7
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