Opinions on my heater wiring work

[surfsup]

I redid the heaters again. I think I did some good work here, everything is tightly twisted right up to the solder pins except tube 1 where due to the solid core it was hard for me to keep it tight so there's a bit of loosening right at the pin. I redid all the heaters and the runs from the mains to the fuse/switch. Updated pics:

http://chicagocadcam.com/ChrisHahn/amp.html

There is still humming and static when maxxed out. I also built an elevation circuit top left of the circuit board above cap1 which elevates the heaters at 45.8v that ties into a two 100R resistor "humdinger-ish" off the lamp.

I'm all ears for more suggestions if anyone has anything for me to try I would appreciate it!

[Structo]

The key thing about heater wires is to try and keep them away from other signal carrying wires.

That is why the Fender amps have them up in the air and why Marshal chose to put them on the floor in the back corner.

You seemed to have combined those two methods but didn't isolate the heater wires from the others.

In your case I would be tempted to do the heaters like Ken Fischer.
Have them on the floor but a lazy loop to each socket to keep the wires away from more sensitive areas.

The tube on the left is fine but the middle one you have the heater wires running through the middle of everything.

I think if you visualize that the heater wires have a corona around them of electromotive waves you will see what I am hinting at.
Keep things away from heater wires or keep heater wires away from other wires.

Although these wires aren't twisted real tight, notice how they are kept away from the other wires?

[soma_hero]

I just finished an amp that would not stay quiet. Everything i did was still humming. Finally switched to DC on the preamp heaters and everything was dead quiet. I've never had to use DC heaters before except on octal preamps, but in this case it was the only solution.

As structo says, keep the heaters away from all signal wires, especially don't make loops around signal wires.

Failing that, try making a DC heater supply. I just used a full wave rectifier with center tap to ground and a 22,000uF smoothing cap. Put out around 7V with 1N4007 diodes, so I used two diodes per side and that dropped it down to 6.3V under load.

[martin manning]

The tube on the left is fine but the middle one you have the heater wires running through the middle of everything.

See attached clip from the AX84 HO layout diagram.

[surfsup]

Martin, I wired it exactly like that diagram the first time (4 heater wire attempts ago, and that was even more noisy than now) - after those failed, I have tried to go "straight across" the socket as some others suggested, which is what I tried now with tighter twists. I also installed a heater elevation circuit putting the heaters at 45.8V. If I disconnect from the lamp and connect a 9V battery, will that be okay to test the heater hum? or maybe "raise" the resistor up higher off the bottom of the socket? Here's a pic of the elevation circuit (handheld with flash - not the best photo)...

[img1200]http://chicagocadcam.com/ChrisHahn/Elevation_small.jpg[/img]

[Structo]

I wouldn't run 6.3v heaters at 9 volts.

[Cliff Schecht]

I wouldn't run 6.3v heaters at 9 volts.

[xtian]

try making a DC heater supply. I just used a full wave rectifier with center tap to ground and a 22,000uF smoothing cap. Put out around 7V with 1N4007 diodes, so I used two diodes per side and that dropped it down to 6.3V under load.

I want to try this on my SE. Can you show a schematic?

[martin manning]

Martin, I wired it exactly like that diagram the first time (4 heater wire attempts ago, and that was even more noisy than now) - after those failed, I have tried to go "straight across" the socket as some others suggested, which is what I tried now with tighter twists. I also installed a heater elevation circuit putting the heaters at 45.8V.

All I can say is that something else must have been causing the hum when you had the socket wired like the layout, because we know that that works, right? Going across the socket can work too, but then the other wires have to be repositioned accordingly.

Testing with a battery supply for the filaments is a very good way to prove that the problem is with the heater wiring. A 6V lantern battery is nice for doing this, but they are rare now. Can you connect four D-cells together? That should last for a little while anyway. Disconnect both transformer heater wires when you try it.

[surfsup]

I think Ace Hardware carries these (they are still on their website and there's a store a block from my house). I will try and get a 6v battery today.

One question please before i do this, can I just detach the solders at the amp light and connect to the battery? I have the elevation circuit and it runs between the C1+ and - for ground, so I'm thinking I can just disconnect the two green/yellow leads at the lamp and connect to the battery since there's already a connection to ground, right?

Sorry for the basic questions, I don't want to fry anything..

[xtian]

Why not use a "wall wart" to provide 6v dc? Sketchy power source, might introduce ground loop or hum of its own?

[surfsup]

I don't have a 6v wallwart. I'll see if I can find a 6v battery somewhere. I wonder if not Ace Hardware, maybe a sports store that sells camping equipment.

[martin manning]

...can I just detach the solders at the amp light and connect to the battery? I have the elevation circuit and it runs between the C1+ and - for ground, so I'm thinking I can just disconnect the two green/yellow leads at the lamp and connect to the battery since there's already a connection to ground, right?

Sorry for the basic questions, I don't want to fry anything..

You can just disconnect the two filament supply leads from the power transformer, and connect the battery (with clip-leads) in their place. Polarity doesn't matter. The filament circuit will still be elevated as before, but the AC supply will be replaced with the DC from the battery.

A wall wart probably will not be very clean (not well filtered), and you will need around 3A current capability... not many wall warts will do that.

[surfsup]

Okay, I will disconnect the two green leads (btm/middle of photo) that run up to the light and clip in the battery.

I have read probably 300 posts on heater wiring, and watched vids and seen pics. I feel like I know less than before. This one clearly shows toward the middle/end that running around the socket with the brown wire is not a big deal. So it seems there is a lot of contradictory info:

http://www.youtube.com/watch?v=rFghwLDO ... re=related

twist
don't twist, use doubled speaker wire
twist tightly
twist just a little bit
2 100R resistors to artificial CT
2 100R resistors don't do anything
run across the socket
never run across the socket
run around the socket
never run around the socket
Come down straight from an inch above the socket
run along the top plate of the chassis
etc

[xtian]

I'm in the same boat, man. I've built three amps so far, all of them SE, and all feature a little annoying hum. I've tried all the things you mention, too, except using DC heaters, so I'm keeping my fingers crossed for you.