Fender Bassman AB165/AA864 issues (120hz, attack, lows)

[RainEnsemble]

Hey forum!
!Short questions in the end of this post!
So i've got a problem with my amp. Originally it was an AB165 blackface bassman with some minor mods (like cut 220k feedback and some 0.01 (?) caps). I didn't like the sound because of HUGE amount of highs, amp always set to treble 0, bass 8.

Then i bring it to an amp tech. He screw the amp a bit. It sounded better on a bass channel, but have a strong 120 hz (100 actually, but it doesnt matter cuz i have 50hz in my country) buzz/hum, whatever you call it. It doesnt change with any volume and disappears with pulling out an output tube

So i opened it up, cut 220k resistors feedback - noise disappeared. Now i have a question - why it was there? Maybe that's a key for another question.

Ok, so i made an Andy Ruhl mod. There started another (and still MAIN) problem: when i hit strings hard, amp pushes a speaker, and it makes low pop, or boom, or whatever. Something like your amp want to breakup, but it told to stay clean. It happens mostly on bridge single pickup of my strat with 3rd string. Also when it happens, the 6l6's are glowing blue. I know thats normal, but it happens mostly when speaker pushed forward by amp.

Also i cut two wires from the bottom of the board: one from 0.1 cap in PI, and another from 47k resistor in PI (according to a chematics). That gave me a bit more volume and overall sound, but the problem is still here

I wanted to bring amp to the basics - AB165, but i dont have needed parts for now, and i think the problem is not that mod. Maybe i'm wrong. who knows

Things that have been done:
1. Changed caps
2. Changed resistors
3. Changed output tubes
4. Cleaned sockets
5. Tested all kinds of cables and guitars
6. Changed diodes
7. Added mid knob for normal channel (just for my taste)

Once again, my main questions:
1. Why there was a 120 (actually 100) hz noise/buzz, when 220k feedback resistors was connected?
2. What can cause the bass pop-boom (also pushing the speaker which looks really scary) and staying clean instead of breaking up when i hit my strings REALLY hard (not touching magnets thou) , mostly on bridge pickup? Could it be a burned ele-cap in a doghouse (and i dont know its dead or something)? Maybe some wrong wiring under the board, which is too hard to fix? I don't know, help me please ;D

Thanks for your posts, guys. I have seen same problems from other guys, but they havent found the answers. Maybe you can help not only me, but also this folks.

[PRR]

Welcome.

It is a mystery.

Me, I would go back to a DEAD-Stock AB165. It wasn't a bad amp. That includes checking ALL resistors, caps, and inspecting ALL solder joints. There's been a lot of work inside there, and bad solder joints are a very "popular" fault, which can cause mysterious troubles.

The AB165 may not be the "perfect" amp. There are several related amps, one of which may suit you better. But I would go back to *exactly* what Fender intended in this chassis, get it to work RIGHT, before messing with "mods" or conversions.

[RainEnsemble]

Welcome.

It is a mystery.

Me, I would go back to a DEAD-Stock AB165. It wasn't a bad amp. That includes checking ALL resistors, caps, and inspecting ALL solder joints. There's been a lot of work inside there, and bad solder joints are a very "popular" fault, which can cause mysterious troubles.

The AB165 may not be the "perfect" amp. There are several related amps, one of which may suit you better. But I would go back to *exactly* what Fender intended in this chassis, get it to work RIGHT, before messing with "mods" or conversions.

Thanks for your reply!
I'll try to get the resistors and caps for stock version (the tech take them out). Maybe that will work. I'll post here anyway about results
But.. May the issue be in a transformers? Or bad caps in a doghouse?

[RainEnsemble]

So... I made my amp look like a AB165 in a PI. Problem with strange attack and bass pop have disappeared, but amp sound a bit thin and trebly. But i think i can fix this changing some resistors
Still don't know where the problem was.

[guitardude57]

Sounds like a cap value is wrong somewhere...  Like a .1 uF accidently replaced with a .01 perhaps...
Compare signal and bypass caps with the schematic.