I finished building a 5F6a Bassman amp.
The amp works, but I get excessive amount of hum. My other DIY tweed amps are practically hum free.
Here are some indications:
- The volume knobs affect the hum (with pots turned down, the hum is completely eliminated)
- The hum is present with or without the guitar plugged in.
- if I use metal pliers to grab the preamp ground bus and force it to the chassis, the hum is reduced noticeably (still not good enough).
- I tried changing preamp tube: no effect.
I used this layout:
Probably has something to do with the preamp or the input stage (because after volume pots there is no hum). I think it is a ground loop somewhere, but I can't find one.
Any suggestion to what might be causing the hum?
The amp works, but I get excessive amount of hum. My other DIY tweed amps are practically hum free.
Here are some indications:
- The volume knobs affect the hum (with pots turned down, the hum is completely eliminated)
- The hum is present with or without the guitar plugged in.
- if I use metal pliers to grab the preamp ground bus and force it to the chassis, the hum is reduced noticeably (still not good enough).
- I tried changing preamp tube: no effect.
I used this layout:
Probably has something to do with the preamp or the input stage (because after volume pots there is no hum). I think it is a ground loop somewhere, but I can't find one.
Any suggestion to what might be causing the hum?
Well, I see neither a center tap on the heater winding, not a virtual center tap on the 6v wires. Virtual center tap being that pair of 100 ohm resistors that were on a zillion Fender amps. One from each side of the 6v to ground. Typically installed on the pilot lamp socket lugs.
Mine does have a center tap for the heaters.
For my previous amps, I used elevated virtual ground.
But it's okay - I just ditched this layout completely, and went with Ceriatone layout for grounding. The hum is now completely gone. 🙄
Don't know what was wrong with previous one, and don't care 😎
The result:
Bassman head + 12 inch cab with Jensen Blackbird. It also has a half power switch (which sound rather nice).
I also made the cabinets (dovetail jointed pine wood). It's been quite a laboursome project, but well worth the effort.
Mine does have a center tap for the heaters.
For my previous amps, I used elevated virtual ground.
But it's okay - I just ditched this layout completely, and went with Ceriatone layout for grounding. The hum is now completely gone. 🙄
Don't know what was wrong with previous one, and don't care 😎
The result:
Bassman head + 12 inch cab with Jensen Blackbird. It also has a half power switch (which sound rather nice).
I also made the cabinets (dovetail jointed pine wood). It's been quite a laboursome project, but well worth the effort.
Sorry to dig up this month old thread, but where did you source the chrome steel plate for the pots and jacks? And how did you make the custom name plates?
Look BEAUTIFUL!! I'm hoping to do a 5F6A clone this summer. Think I will layout a custom board for it, just for fun.
please post the ceritone layout as I used the above one with the same result. if it fixed yours it may fix mine too.
- Status
- Not open for further replies.