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1: On the schematics there is a .05 μf capacitor from the fuse to ground. I assume that this is no longer needed with a three wire power cord. I took about a 10 year vacation from building due to "life". I have several unfinished builds and some finished. I know that I didn't use the cap on any of them but I forget why and am assuming this is the reason. Am I correct?
2: I have a 5F1 that I thought was OK but I 'think' I have a 120 cycle hum... I've been talking with a boutique builder in my area and from what I've told him, he thinks that is what I have. He is on vacation and I am not going to bother him so I'll ask here. Am I correct in assuming that a 120 cycle hum is DC and therefore coming from somewhere post rectifier? The PT is a New Sensor and I noticed that I accidentally burned a little insulation off both the black with white writing wires coming from the PT, one to the fuse and one to the volume/switch. The place on the wire to the fuse is pretty bad, the place on the wire to the pot is minimal, maybe not all the way through. I am going to use some high quality electrical tape to fix the skinned places... but I am not sure if this will suffice. What do you think?
Also, I took a shortcut on grounding. I grounded the power cord to a lug on the PT, I ran all the other grounds to another lug, using star washers... I think this was a mistake. I am going to pull all the grounds and make a 22AWG solid wire grounding bus, like someone else posted on this forum. I'll run the grounding bus from the first input jack to the chassis, then back across toward the switch and fuse... I wish I could remember who posted this idea, but thanks! So, I'll use short leads to the grounding bus.
I am going to add the 25uf cap parallel with the 1.5k cathode resistor.
I also twisted the 6.3v wires from the pilot to pins 2 and 6 of the 6V6 but neglected to twist them from there to the 12AX7. I'm thinking I should remove them and add twisted wires. I'll run them close to the outside of the chassis, as opposed to close to the board. Does this sound good?
Please comment on anything and everything. I have already checked the filter caps, I have no voltage.
I guess mostly I need to know what of these things is likely to induce a low hum. It is not a buzz but a hum, it is low. It gets louder as I increase the volume and plugging into either of the jacks changes nothing, plugging in a guitar and touching the strings changes nothing re the hum. I have a SF Champ I set in the same spot and plugged into the same outlet, both amps facing the same way and the SF is quiet while the 5F1 has the hum. ALSO.. there seems to be a definite decrease in the volume of the 5F1. The SF is at least twice as loud, maybe more. Another thing that was mentioned to me is that it is possible that the PT is bad.
All these other things really need to be fixed so I will try them first. Then if it isn't right I'll swap out the PT. I think I have another one just like it NIB. I have a couple of other PTs that are different brands too. OH, I have swapped the tubes twice just to be sure.
So thanks for any ideas!
Julien
2: I have a 5F1 that I thought was OK but I 'think' I have a 120 cycle hum... I've been talking with a boutique builder in my area and from what I've told him, he thinks that is what I have. He is on vacation and I am not going to bother him so I'll ask here. Am I correct in assuming that a 120 cycle hum is DC and therefore coming from somewhere post rectifier? The PT is a New Sensor and I noticed that I accidentally burned a little insulation off both the black with white writing wires coming from the PT, one to the fuse and one to the volume/switch. The place on the wire to the fuse is pretty bad, the place on the wire to the pot is minimal, maybe not all the way through. I am going to use some high quality electrical tape to fix the skinned places... but I am not sure if this will suffice. What do you think?
Also, I took a shortcut on grounding. I grounded the power cord to a lug on the PT, I ran all the other grounds to another lug, using star washers... I think this was a mistake. I am going to pull all the grounds and make a 22AWG solid wire grounding bus, like someone else posted on this forum. I'll run the grounding bus from the first input jack to the chassis, then back across toward the switch and fuse... I wish I could remember who posted this idea, but thanks! So, I'll use short leads to the grounding bus.
I am going to add the 25uf cap parallel with the 1.5k cathode resistor.
I also twisted the 6.3v wires from the pilot to pins 2 and 6 of the 6V6 but neglected to twist them from there to the 12AX7. I'm thinking I should remove them and add twisted wires. I'll run them close to the outside of the chassis, as opposed to close to the board. Does this sound good?
Please comment on anything and everything. I have already checked the filter caps, I have no voltage.
I guess mostly I need to know what of these things is likely to induce a low hum. It is not a buzz but a hum, it is low. It gets louder as I increase the volume and plugging into either of the jacks changes nothing, plugging in a guitar and touching the strings changes nothing re the hum. I have a SF Champ I set in the same spot and plugged into the same outlet, both amps facing the same way and the SF is quiet while the 5F1 has the hum. ALSO.. there seems to be a definite decrease in the volume of the 5F1. The SF is at least twice as loud, maybe more. Another thing that was mentioned to me is that it is possible that the PT is bad.
All these other things really need to be fixed so I will try them first. Then if it isn't right I'll swap out the PT. I think I have another one just like it NIB. I have a couple of other PTs that are different brands too. OH, I have swapped the tubes twice just to be sure.
So thanks for any ideas!
Julien
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