Tweet
I just completed a complete rebuild of my AB165. This is my first project of such scale. I added the bias mod, and the phase inverter mod that is pretty common (moving back to aa864 specs). I have attached my layout of the amp so you can see what I am talking about. After I created this layout I added some mods to the bass channel tone stack that aren't on this layout, but I don't think that is critical because the problem occurs on normal channel also.
The amp turns on with no smoke, which is great, and I am hearing sound with no hum, which I thought I would have to battle.
However, it sounds like it has no power (has low output) and it has a lot of tube-sounding distortion (basically sounds like I have a tube screamer on it when I am running straight into it). This happens regardless if I use the bass channel or normal channel. I have double checked what is in the amp to what is on the layout. Does anyone see anything obviously wrong with the layout?
Both tubes are biased to around 39ma. This is what I had it set to before I gutted the amp and rebuilt it, and it was much more powerful then. I have switched around the preamp tubes to make sure that wasn't the problem.
I am thinking the problem lies in the power amp section or phase inverter, but I need some guidance on what to look for. I checked the voltages on power tubes, and they all seem exactly like they were previously. B+ is what it used to be. The only thing that seemed a little out of the ordinary was that the voltage coming off the 470 ohm resistor and going to pin 8 of the PI was around 80V, which seems lower than what it should be. Would this be enough to cause this kind of problem?
I appreciate any help or suggestions you can offer. Thanks! josh
The amp turns on with no smoke, which is great, and I am hearing sound with no hum, which I thought I would have to battle.
However, it sounds like it has no power (has low output) and it has a lot of tube-sounding distortion (basically sounds like I have a tube screamer on it when I am running straight into it). This happens regardless if I use the bass channel or normal channel. I have double checked what is in the amp to what is on the layout. Does anyone see anything obviously wrong with the layout?
Both tubes are biased to around 39ma. This is what I had it set to before I gutted the amp and rebuilt it, and it was much more powerful then. I have switched around the preamp tubes to make sure that wasn't the problem.
I am thinking the problem lies in the power amp section or phase inverter, but I need some guidance on what to look for. I checked the voltages on power tubes, and they all seem exactly like they were previously. B+ is what it used to be. The only thing that seemed a little out of the ordinary was that the voltage coming off the 470 ohm resistor and going to pin 8 of the PI was around 80V, which seems lower than what it should be. Would this be enough to cause this kind of problem?
I appreciate any help or suggestions you can offer. Thanks! josh
Attached Files
This project might motivate me to finally get some more, because it would sure be helpful in tracking down the problem...
Comment