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Hey everyone! Great news! The rebuild went really well and the issue has been resolved! It must have been the conductive boards! There is still the tiniest amount of hum but I'm gonna chock that up to not completely replacing the boards and the weird off brand power transformer. But a huge...

I’m still working on this. It’s taking a while to get back together as work has been really busy.

Thanks I hadn’t really looked at the 864 much since I don’t want to do that level of changing the preamp circuit. Wiring it up as per the schematic makes sense, even just for a sanity check. It’s tough getting advice from a bunch of sources, some say do this some say don’t and it contradicts...

Thanks yeah I forgot to add that resistor back in there. I’m using the power amp section from the AA165 since it’s closer to the AB165.

Ok here are those cleaned up boards! This is the modified layout I'm planning to use to rebuild. Does anyone have any suggestions or see any potential issues?

Ok so I cleaned the boards off with a scotch bright pad and iso alcohol. I let them dry and they were looking good as new, all nice and evenly grey colored. Then I put them in the oven at 175°F for an hour so far and they’ve gotten a lot darker grey and kinda splotchy in some areas. I took one...

You'd think right! The closest one is about 30 minutes away, and they don't have much for projects like this, mostly just little 1/4-watt resistors and little caps. They may have the correctly rated diodes, but I wouldn't put money on it. A little update on progress... after testing the board...

Well the shipping for 7 diodes is a lot more than the diodes themselves so if I have to order anything else for the build I’ll get them swapped out but if not I’m gonna let them ride.

I have the amp completely ripped apart right now and going to rebuild after cleaning the boards. That resistor is the grid bias resistor and I had it replaced with a 1.5K resistor and a 25k pot for adjusting the bias.

You can look at the scope output here. It looks like ~50mV idle. It's pretty obnoxious. I have played another BF Bassman before and it was nothing like this, this amp is clearly broken somehow.

I feel like I've ruled this out. I have all new tubes, and the hum is the same as the old tubes and any combination of tubes in various sockets. I don't have another amp or tube tester that will allow me to be 100% sure a tube is good, but I think I'd be very unlucky to have 2 complete bad sets...

Thanks for the advice! I didn't realize the tricky part of asking for help online would be deciding what to try next 🤣. I'm pretty sure you're the only one so far on my threads that doesn't think what I have for grounding is absolute ****! Although there is that ground loop... I'll take good...

I will be taking the whole amp apart, testing the boards for conductivity, and cleaning or replacing them. I'll put it back together according to Fender's stock layout to avoid any ground issues I may have introduced. I tried to get some solid photos of the whole amp and closeups of key areas...

Yeah it's solid, it's just hard to see in the photo.

I can switch the OT primaries if that 100% eliminates this as an issue. The OT is the original 125A13A listed on the schematic so the colors should match. Just to clarify, the hum is not in the power section. when V4 (Phase inverter) is removed the amp is silent. So that makes me think this...

Ok I'm continuing to work through various possible solutions here. Again, I really appreciate everyone's help! I have double checked, and the capacitors are good, no current leaking. Although I do get DC voltage reading to ground. Is this normal? See my previous post for values. I tried...

Ok so this morning I got some time to monkey with this amp again. I pulled V1 & V2 together and the noise is still there but it's at ~50% volume. I lifted one end of each of these caps and measured the DC to ground. Here's what I found: C03 0.040V / 212V = 0.02% (new silver mica) C04 0.147V /...

I’ll give isolating those jacks from the chassis a try and report back.

Yeah the switches do make good contact. I wish this was the fix! But I only attached the bus to the ground tab of the bass channel jack. It’s attached to the switch tab only on the normal channel jack. Although the input circuit is quiet complicated at the jacks so if I missed something and it...

Thanks for the suggestion! All the resistors are new and tested so that’s unfortunately not our noise maker.

Hey Antony thanks for taking the time to go over this and help! It’s a 1965 Bassman, AB165 circuit (with a few mods like bias level pot, switchable NFB loop and humdinger heater pot). The schematic I linked is accurate to what’s in the chassis. The noise is a hum. It sounds to me like 60Hz...

Hey everyone! I'm looking for some experienced members to help me sniff out what is going on with this amp, any help would be greatly appreciated, however I have tried a lot of different things already so please read the long story! The long story not so short. I got this amp on Ebay for a...