Hi All
An earlier thread inpired me to dust off the old 555 for a minor tune up. 2 mods were completed with one remaining.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=53551&perpage=35&pagenumber=1
Mod 1 ) Add inrush current limit. This mod is mainly to prevent documented premature failure of the on/off power switch and generally a good thing for larger power amps.
Installed a 3 ohm 15W in series with the Xfrmer primary. Use a 13A NO relay contact to short the resistor when the secondaries come up. The 125 Vdc relay coil senses across both rails of one Amp. Added a 1N4005 free wheel diode on the coil. A 5K resistor drops the +/- 82 V rails to a nominal 120 relay volts.
Mod 2 ) Add film bypass caps across each of main caps (15000 uF 100V 4 places).
I added 2.7 uF 250V mylar film. Some people say to add 100-22 uf electro.
Mod 3 ) Change driver transistors. I still have this to do. I am having trouble finding sources for mje15030/31 TO-220 parts.
Checked digi and mouser so far.
An earlier thread inpired me to dust off the old 555 for a minor tune up. 2 mods were completed with one remaining.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=53551&perpage=35&pagenumber=1
Mod 1 ) Add inrush current limit. This mod is mainly to prevent documented premature failure of the on/off power switch and generally a good thing for larger power amps.
Installed a 3 ohm 15W in series with the Xfrmer primary. Use a 13A NO relay contact to short the resistor when the secondaries come up. The 125 Vdc relay coil senses across both rails of one Amp. Added a 1N4005 free wheel diode on the coil. A 5K resistor drops the +/- 82 V rails to a nominal 120 relay volts.
Mod 2 ) Add film bypass caps across each of main caps (15000 uF 100V 4 places).
I added 2.7 uF 250V mylar film. Some people say to add 100-22 uf electro.
Mod 3 ) Change driver transistors. I still have this to do. I am having trouble finding sources for mje15030/31 TO-220 parts.
Checked digi and mouser so far.
Attachments
Dear Mr DJK,
Thank you for helping me find the driver transistors!
The alternate parts you suggest have about 1/2 the current and x2 voltage. My main concern is the hfe specs are quite different (much lower from Ic=1A on). They are both 50W devices.
Do you think this is OK ?
Also, are SOA specs a good thing to compare for alt. drivers?
FYI I have started to remove the old parts today. Darn Adcom they super glued the thermistor to the TO-220 driver case. I hope a razor between can seperate them. I really don't want to hunt for new thermistors too.
Thank you for helping me find the driver transistors!
The alternate parts you suggest have about 1/2 the current and x2 voltage. My main concern is the hfe specs are quite different (much lower from Ic=1A on). They are both 50W devices.
Do you think this is OK ?
Also, are SOA specs a good thing to compare for alt. drivers?
FYI I have started to remove the old parts today. Darn Adcom they super glued the thermistor to the TO-220 driver case. I hope a razor between can seperate them. I really don't want to hunt for new thermistors too.
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