kasbah512
Member
I started trying to repair this receiver, and I'm concerned for a few reasons. Primarily that there is no DC bias adjustment, and considering I had some blown transistors, including the outputs that I replaced (for some with a 50% higher gain).
For the most part, everything is functional, except the fact that when there is no load on the speaker output I get the volume indicator showing that there is some output. I'm also waiting on new capacitors for this unit, and I'm assuming that since we may have had some over voltage issues, it may fix that issue...
I have read that there wont be an increase in power output from increasing gain of output transistors, but this doesn't quite make since to me.... I've read that the "entire circuit determines the output" but i suppose something isn't clicking. I could understand maybe a safety issue related to this, but not a failure to increase power. I tried to match the replacement transistors on the pre-driver and power amp as close as possible to gain, but they aren't exact replacements. The outputs are what scare me most I suppose. The gain on the originals was reading 98 hFE and the new ones are around 150. While I could find exact replacements for them, I really don't want to throw more money at this thing. It was a goodwill find.
1) Have I done something that may affect dc bias, as this unit has no adjustment?
2) Have the changes I've made posed a safety risk?
This amp is for a friend of mine so I definitely don't want it to go up in smoke. I want them to have a quality receiver that will hopefully last until the new caps go bad. This beast is at least 125 WPC, but I'm convinced its putting out more.
For the most part, everything is functional, except the fact that when there is no load on the speaker output I get the volume indicator showing that there is some output. I'm also waiting on new capacitors for this unit, and I'm assuming that since we may have had some over voltage issues, it may fix that issue...
I have read that there wont be an increase in power output from increasing gain of output transistors, but this doesn't quite make since to me.... I've read that the "entire circuit determines the output" but i suppose something isn't clicking. I could understand maybe a safety issue related to this, but not a failure to increase power. I tried to match the replacement transistors on the pre-driver and power amp as close as possible to gain, but they aren't exact replacements. The outputs are what scare me most I suppose. The gain on the originals was reading 98 hFE and the new ones are around 150. While I could find exact replacements for them, I really don't want to throw more money at this thing. It was a goodwill find.
1) Have I done something that may affect dc bias, as this unit has no adjustment?
2) Have the changes I've made posed a safety risk?
This amp is for a friend of mine so I definitely don't want it to go up in smoke. I want them to have a quality receiver that will hopefully last until the new caps go bad. This beast is at least 125 WPC, but I'm convinced its putting out more.
