i have acquired a dynaco 150, she in a bit of a sorry state due to the previous owners tinkering, it runs but has intermittent noise in one channel, so instead of the usual recap and rebuild i was wondering if anyone had used the chassis and transformer and built something completely different inside, maybe a leach? not really interested in the update my dynaco path. so fire away, who has done what and what are some ideas. cheers.
I like the $3 absolute protection against blowing my $600 retail speaker with DC, the output capacitor. The transformer is single winding, so leach or any split supply speaker burner is not possible. With DIY construction, 20000 hour life without a solder joint letting go is highly unlikely. One joint lets go in the wrong place, DC is inevitable.
I've done one side of my ST120 with an Apex AX6, much better low wattage sound with fewer parts. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html
The other side I left with the undamaged PC14, but improved the low wattage crossover distortion with the djoffe idle bias current control. https://www.diyaudio.com/forums/solid-state/156627-dynaco-stereo-120-beautiful.html
Output transistors upgraded to MJ15003, still located on the heat sink remote from the driver board. I included more heat sink. A Pentium II heat sink would be ideal, but I only salvaged 1 which I used for the DC voltage regulator. Repaired PC15 regulator was not compatible with modern high gain transistors, was current tripping at 2 amps instead of OEM 6.5. OEM heat sink was capable of only the 1 hour FTC test, and blew the output transistors run at 10 w/ch into 4 ohms for 3.5 hours. DC is regulated to 70 v, which can produce 75 w on 2 channels for 5 seconds into my 8 ohm speakers.
Of the two sides the AX6 is more reliable. djoffe board has blown the current sense transistor twice, going to 200 ma idle bias current as a result. Fans prevented damage. Both sides sound equivalent up to 75 w/ch with my .03% HD CS800s. I use top octave solo grand piano and tinkly bells (Martin Denny Hawaii) as test tracks. ST120 uses less electricity than CS800s.
I've done one side of my ST120 with an Apex AX6, much better low wattage sound with fewer parts. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html
The other side I left with the undamaged PC14, but improved the low wattage crossover distortion with the djoffe idle bias current control. https://www.diyaudio.com/forums/solid-state/156627-dynaco-stereo-120-beautiful.html
Output transistors upgraded to MJ15003, still located on the heat sink remote from the driver board. I included more heat sink. A Pentium II heat sink would be ideal, but I only salvaged 1 which I used for the DC voltage regulator. Repaired PC15 regulator was not compatible with modern high gain transistors, was current tripping at 2 amps instead of OEM 6.5. OEM heat sink was capable of only the 1 hour FTC test, and blew the output transistors run at 10 w/ch into 4 ohms for 3.5 hours. DC is regulated to 70 v, which can produce 75 w on 2 channels for 5 seconds into my 8 ohm speakers.
Of the two sides the AX6 is more reliable. djoffe board has blown the current sense transistor twice, going to 200 ma idle bias current as a result. Fans prevented damage. Both sides sound equivalent up to 75 w/ch with my .03% HD CS800s. I use top octave solo grand piano and tinkly bells (Martin Denny Hawaii) as test tracks. ST120 uses less electricity than CS800s.
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Looking at the PC36 schematic, there are 2 fuses, plus and minus. There is a ground input to the board. That indicates dual winding transformer. Sorry, I did not look. Better install a protection board suitable for disconnecting the speakers with a relay if DC on speakers occurs. Or use $50 throwaway speakers.