1965 Bassman Noise 🤷‍♂️

Jasonpatrick

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Also. Just one thing with the hum. Did you ever adjust the hum balance? I’m sure you know this but in the ab165 it’s not a bias pot . Its to balance the signal. Maybe I missed that you tried that.
 

CodySorgenfrey

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Yes. Don’t use that schematic for the power section. That is missing a bias grid resistor for a power tube. If you are gonna take off the noise suppression oscillation cbs additions from the power section then use the aa864 Bassman schematic for the power side then use the ab165 for the preamp.
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.
 

CodySorgenfrey

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And just some unsolicited advice, whenever I’m having a problem tracking something down in a modified amp, I always always wire it back up as per the schematic for that specific amp and then go from there. Happy turkey day!
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. In the end I don’t have an iron big enough to solder to the chassis like the original calls for so I’m trying to get close without that. Maybe I should see if I can get the AB165 circuit to even work quietly without changing anything. The only reason I’m thinking of doing the AA165 power section is because it’s a lot simpler so hopefully that’ll make this easier and not more complicated.

Happy thanksgiving all!
 

Jasonpatrick

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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. In the end I don’t have an iron big enough to solder to the chassis like the original calls for so I’m trying to get close without that. Maybe I should see if I can get the AB165 circuit to even work quietly without changing anything. The only reason I’m thinking of doing the AA165 power section is because it’s a lot simpler so hopefully that’ll make this easier and not more complicated.

Happy thanksgiving all!
I noticed you don’t have a big iron. What you can do since this isn’t gonna be a collector piece, drill holes in the chassis in front of the brass plate and attach some of them ground tabs. In fact, use them for wherever you need to ground to chassis. They will fit under the power tube screws and on the power transformer studs. #6 I think it is… anyways, then you know you have a secure connection to ground. See how they did it on this for example.
 

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Jasonpatrick

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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. In the end I don’t have an iron big enough to solder to the chassis like the original calls for so I’m trying to get close without that. Maybe I should see if I can get the AB165 circuit to even work quietly without changing anything. The only reason I’m thinking of doing the AA165 power section is because it’s a lot simpler so hopefully that’ll make this easier and not more complicated.

Happy thanksgiving all!
Also also, I know many folks will tell you to remove the noise suppression/ oscillation stopper set up on the power tubes and hum balance on the ab165, but there is a reason Fender added them. Just food for thought:)
 

CodySorgenfrey

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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 improvement over all!

I rebuilt it 100% back to fender spec for the AB165 except for no soldering to the chassis (instead I used lugs on bolts in similar locations), then after finding the issue was resolved I went forward with installing some mods.
1. A humdinger pot with resistors to balance and lower heater voltage.
2. A pot for bias level.
3. A master volume pot.

Thank you everyone for the help, I really appreciate it!

IMG_3216.jpg
IMG_3219.jpg
 

chas.wahl

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Glad to "hear" it.
That camera has serious fisheye, no? It looks like your knobs at the extremes are being sucked into competing black holes.
 




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