Have a question:
I just completed a restoration on an AU-919 that had to have all of the output transistors replaced (modified with NJW3281/1382) because 3 completely shorted. On the channel that blew, one of the drivers shorted as well, so after some research I wound up with TTC004B/TTA004B as substitutes (side note: these require a solder tag/ring to be attached to the collector and the screw feeds through this. MAKE SURE these go in correctly! I didn't do it right at first and couldn't bias the channels. They're the reverse pinout of what came out, so I had to mount them upside down, which for these is fine because they're full-plastic body). And yes, I put in new ones after that, just because.
The amp works great and sounds great. I'm really happy with the work I did on this one in particular. My question is, and I don't know if it's even a big deal, but when I first power it on, it comes out of protection and if I'm measuring the bias voltages, one channel creeps up to about 170mv while the other maintains at around 35mv until the higher one stabilizes and then starts to drop back to normal. Once it gets back to around the 22mv mark the other channel joins in and they both settle between 18-19mv which is basically where I want it.
I did notice it was very touchy getting the bias voltages stable, even with all new trimpots, caps, film caps, transistors... Again, maybe not even an issue, but just wondering if that is normal or if there is something else being funky? First time doing a 919 and it was a bear; the 717 was nowhere near as painful to restore as this was.
I just completed a restoration on an AU-919 that had to have all of the output transistors replaced (modified with NJW3281/1382) because 3 completely shorted. On the channel that blew, one of the drivers shorted as well, so after some research I wound up with TTC004B/TTA004B as substitutes (side note: these require a solder tag/ring to be attached to the collector and the screw feeds through this. MAKE SURE these go in correctly! I didn't do it right at first and couldn't bias the channels. They're the reverse pinout of what came out, so I had to mount them upside down, which for these is fine because they're full-plastic body). And yes, I put in new ones after that, just because.
The amp works great and sounds great. I'm really happy with the work I did on this one in particular. My question is, and I don't know if it's even a big deal, but when I first power it on, it comes out of protection and if I'm measuring the bias voltages, one channel creeps up to about 170mv while the other maintains at around 35mv until the higher one stabilizes and then starts to drop back to normal. Once it gets back to around the 22mv mark the other channel joins in and they both settle between 18-19mv which is basically where I want it.
I did notice it was very touchy getting the bias voltages stable, even with all new trimpots, caps, film caps, transistors... Again, maybe not even an issue, but just wondering if that is normal or if there is something else being funky? First time doing a 919 and it was a bear; the 717 was nowhere near as painful to restore as this was.