Gr8Scott
Wookieologist
All I need to do at this point is bias the amp and put it back together. It's as blackfaced as I'm going to be able to make it. The new board went in without much of a hitch. If I had taken a bit more caution in putting it in, it would look a little better (the wire running from the feedback circuit to the speaker out has a wire nut on it). There is another wire nut on a 400+ volt wire that doesn't belong in the AA864 circuit that was used in the AA371 circuit to make it cleaner sounding. I just bent the wire back on itself and put the nut on there to prevent shorts. I'll hot glue the end of it so it won't come undone. Same with the feedback wire I guess, though I should probably do something more professional looking like shrink tube it or something. I did solder the wire before I wire nutted it together. I just wanted something other than solder and twisted wire holding that connection together. When I fired it up, I got a spark off the 1K resistor in the bias circuit which should have been changed to a 470 ohm resistor, but I forgot. I changed that plus removed the extra resistor in line between the bias pot and ground and replaced that with solid wire. Then I fired her up and got sound (I was SOOO happy). Unfortunately, I was getting very little volume and I knew the tubes weren't bad. That meant my wiring was bad, so I set about trying to figure out what I had missed. I could plug into the extra speaker and get low volume sound (it sounded pretty good though) and if I plugged into the regular speaker jack I got uncontrollable microphonic squealing like you wouldn't believe. It's the most annoying/frightening noise anything could ever make. Someone should use it in a horror flick at the moment when the monster attacks. I figured that I must have something in the wiring of the output tranny and the feedback circuit wrong 
mg:. I was way right. The AA371 has the OT outputs wired in reverse to the AA864. I reversed the wires and SHAZZAAAAM!!! :beerchug: Sweet sweet loud volume and no smoke, no squealing and that bass channel sounds really good now. It is really useable for a change. This whole board is night and day better than the original. I might wire in a 1 ohm resistor temporarily to see what the bias is for now until I can get in two test probe points and 1 ohm resistors to put in permanent bias test points. No sense in stopping until I've really given this girl all the trimmings. Speaking of trimmings, she now has all the standard blackface accoutrements. She has the blackface logo and the blackface faceplate to match her blackface style grillcloth.
IMHO - If you have an AA371 circuit like I did. Do what I did and replace the whole board. It's not frightfully easy to do and it requires a bit of time to get the project done, but the changes you would have to make to the AA371 circuit to make it even a passing resemblance to the blackface circuit is just too much work with limited returns. This amp went from zero to hero in a few days time. I got my parts Friday and had it running on Monday night. I also managed to party at a friend's house Saturday night and eat dinner with my parents on Sunday night along with doing my job on Friday/Monday. I also watched Chuck/Heroes/Life last night before completing the amp. Total hours spent working on the amp at this point would be 20 not counting the obsessive scheming to get to this point. :beerchug:
mg:. I was way right. The AA371 has the OT outputs wired in reverse to the AA864. I reversed the wires and SHAZZAAAAM!!! :beerchug: Sweet sweet loud volume and no smoke, no squealing and that bass channel sounds really good now. It is really useable for a change. This whole board is night and day better than the original. I might wire in a 1 ohm resistor temporarily to see what the bias is for now until I can get in two test probe points and 1 ohm resistors to put in permanent bias test points. No sense in stopping until I've really given this girl all the trimmings. Speaking of trimmings, she now has all the standard blackface accoutrements. She has the blackface logo and the blackface faceplate to match her blackface style grillcloth.IMHO - If you have an AA371 circuit like I did. Do what I did and replace the whole board. It's not frightfully easy to do and it requires a bit of time to get the project done, but the changes you would have to make to the AA371 circuit to make it even a passing resemblance to the blackface circuit is just too much work with limited returns. This amp went from zero to hero in a few days time. I got my parts Friday and had it running on Monday night. I also managed to party at a friend's house Saturday night and eat dinner with my parents on Sunday night along with doing my job on Friday/Monday. I also watched Chuck/Heroes/Life last night before completing the amp. Total hours spent working on the amp at this point would be 20 not counting the obsessive scheming to get to this point. :beerchug:
