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Filament Wiring? Pin to Pin Specific?

littlejohn

Member
Messages
999
Most of the posts you read on Filament wiring talk about ways to do it, lead dress, but I just finished watching the Tube Depot video and there is not much mention of landing on the specific pin at the next tube or tubes down the line...does it matter. Fender used to wire all their heaters with two solid green twisted wire I suppose, and you'll see the same on new tweed builds now all the time by the kit builders that keep cropping up, which I assume is just random running tube to tube as I never see any left over sharpie marks or anything on the heaters where they meet the tubes? I can't see Fender worrying/taking time about this years back either when the ran the green pairs.

So, does it matter if say you leave pin 7 of a 6v6 tube and land on pin 2 at the next one?...or leave a pin 9 and go to pin 4/5 the tube?..with the other wire in the twist, or is it all just one big circuit of 3 volts per side? I mean did Fender worry about this years back before say the BF amps, but then why go to the different colored wires, Black/White, etc, for each heater wire in the twist?

Is there a phasing? scenario that comes into play regarding the hum cancellation, wondering if it even matters, just voltage going from tube to tube?

Maybe I've just been lucky as my few tweed builds are very quiet and I've never bothered to tone out/mark one of the green wires when I go to land it at the next pin/tube over?
 

SatelliteAmps

Member
Messages
6,170
Yes it can matter, if the wiring is done right.

Just because Fender did something, does not mean it is the best way to do things. All it takes is a basic meter and you can follow filament wiring regardless of color of wire. You can even test Fenders out to find out if they followed it or not.
 
Messages
826
It does matter for push-pull power stages. You should connect one 'colour' heater wire to the same number pin on every power tube. Any hum pick up from the heater inside the tube will then be 'in phase' for all the power tubes. The push-pull connection will then cancel that hum.
 

RiftAmps

Member
Messages
207
I connect them like so:

Filament wire #1 - Octal power tubes pin 2 - Noval preamp tubes pin 9

Filament wire #2 - Octal power tubes pin 7 - Noval preamp tubes pin 4+5

As mentioned above, it's all about keeping it in phase so any hum can then be cancelled.
 

axpro

Member
Messages
628
I tend to use 2 different coloured wires in a tight twist when wiring filaments. that way i can wire all the tubes the same. There were times i didn't take the time to do it, and to be honest i don't remember there being any issues whatsoever. but I prefer the neat and tidy way i do it now.
 
Messages
826
I tend to use 2 different coloured wires in a tight twist when wiring filaments. that way i can wire all the tubes the same. There were times i didn't take the time to do it, and to be honest i don't remember there being any issues whatsoever. but I prefer the neat and tidy way i do it now.
I agree. When I am building an amp, if there are two (or more) ways of doing something, I always try to work out which way is 'right' or 'better', even if it probably makes little difference.

That way, if you do get more hum than you want (for example), you have at least already eliminated some of the possibilities, when you start to track it down.
 

littlejohn

Member
Messages
999
Thanks for the replies on this, sounds like it's best to tone out and wire them correctly , at the very minimum for the power tubes. Good stuff...
 
Messages
232
Decide on the length you'll need, and pull twice that much wire. Find the middle by doubling it over and run a black marker down one half of the wire to make a long black line on your presumably green wire. Now put the two sides back together and use your power drill or crank drill or whatever you use to twist the wire. Then use your method of choice for connections and it'll be easy for anyone (including you) to take one look and know exactly what you did.
 

Diablo1

Member
Messages
620
Heater wire polarity doesn't matter on the input stages, but as has been posted above, can reduce hum on push-pull output stage. More important is to make sure your heater wires connect first from the PT to your output tubes and then on the string to the input tubes. This minimizes the current draw in the wires near the sensitive input stage. Output tube heaters draw significantly higher current than 9-pin preamp tubes.
 

EFK

Silver Supporting Member
Messages
1,107
They don't need to be "twisted" which - depending upon how tightly they are twisted - can add a lot of unnecessarily extra wire. The two wires simply need to be closely adjacent to each other. Many a vintage 40s or 50s off-brand amp simply run the two filament wires in a pair right next to each other (i.e., side by side) and have no more filament hum than a typical Fender or Marshall. Especially in the preamp sections, I don't see any reason to tightly spin 6 or 8 inches of wire when a single short 1" or so piece ***carefully routed perpendicular to the grid and plate wiring*** will serve to link tubes. Like they say in real estate, Location location location!
 

Geetarpicker

Member
Messages
3,024
I worked on a mid 60s Bassman head last week that had miswired filaments from day one. It hummed (even with all the preamp tubes and PI tube removed) and probably always did to an extent. The short story was the filament phase (wiring) does matter at least for the output tubes...

In that Bassman head the output tube filaments swapped phase between the two. That said, the output tubes should be wired pin to pin the same. Then any hum in the two output tubes cancels out in the OT since it's a push pull setup. On that amp the filaments on the 6L6s were actually out of phase (wiring swapped between the two) so the natural hum cancelling properties did not work. Swapping the wires on one of the output tubes fixed the hum. A little tricky to spot since the filaments were all the same color green wire. Anyway I've heard that the correct Fender wiring is the to keep the polarity the same for the outputs and PI tube, then swap phase at each preamp tube from there on up to v1. That said, on the amp I worked on every tube from the 6L6s onward swapped polarity, even the PI. I tried also putting the PI in phase, and the rest swapped (just to see what would happen) but it didn't have any effect and was just as quiet either way. In the end though, specifically having the 6L6 filaments wired pin for pin identical was essential for the least amount of hum.
 

guiltless

Member
Messages
1,494
I always run the pre's in parallel. It's dead quiet and much easier. I also angle the sockets to accommodate. I run the power in twisted because it's easier and it's dead quiet.

That's the goal. The easiest way possible and ensuring that it's dead quiet.

I also make sure I am consistent from pin to pin. I have never tried not doing it. The inconsistency itself would bug me even if it didn't make a noise difference. Plus, with the parallel wiring, it's automatic.

Here are a couple of pics of my XB-1 model.




Sent from my iPhone using Tapatalk
 

swiveltung

Senior Member
Messages
14,485
Some old Fender amps are wired correct and some are not. I always look when I'm in there. It doesn't seem to make a lot of difference I guess as some of these amps have been used for 50 years as they are. But I do like to have them correct.
 

larsjm

Member
Messages
52
Oh ****, here we go....

{insert snake oil here}
Exactly. It seems the more vintage tube amps you look at, the more opinions of how to wire the heaters there are. Yet, if these opinions were actual solutions, then they should work at least 75% of the time. In my experience, that isn't even close to the case. Twisted wires, no guarantees. Ground elevation, no guarantees. DC heater circuit for your preamp tubes, no guarantees. Change the grounding scheme on the entire amp, no guarantees. These are really all just guesses that people carve into stone as if they're laws of amp building. You can end up wasting a bunch of time trying everything and none of it gets rid of the hum.
I've seen some of the cleanest, nicest guts of tube amps where every filament wire is perfectly twisted and laid out, and the amp hums. Then there will be an old amp where it looks like they didn't care where any of the wires went, and they did everything "wrong", and the amp is dead-quiet. The original heater wiring on a vintage 5E3 was a complete "No-No" according to "expert boutique amp builders", yet from the video clips I've watched, an original Deluxe works perfectly fine (and do you really want to take an iron and go hacking up the wiring scheme on an all-original '57 Deluxe? Not likely).
Personally I think it all comes down to your power transformer. Some are junk, and some are outstanding. The good ones are built in such a way that they don't bleed a bunch of noise into your heater winding to begin with. The bad ones bleed so much noise onto the heater winding that no amount of the typical guesses is going to fix it. Maybe that "death cap" was actually in there for a reason???
 

PushedGlass

Member
Messages
734
Speaking of which, with respect to vintage Fender amps is there a thing about leaving the shield disconnected on one of the reverb tank cables?
 

xtian

Gold Supporting Member
Messages
2,582
I think it all comes down to your power transformer. Some are junk, and some are outstanding. The good ones are built in such a way that they don't bleed a bunch of noise into your heater winding to begin with. The bad ones bleed so much noise onto the heater winding that no amount of the typical guesses is going to fix it.
All of the lead dress best practices you mention are just best practices. You may find other solutions that work for you, but that's no reason to toss out best practices.

Consider that ALL power transformers radiate 60Hz hum that can be coupled into the output transformer, and you will hear that hum at the speaker. Proper orientation and placement of the PT and OT is required to avoid this audible hum. The PT is NOT bleeding noise into the heater winding...the heater winding is 60Hz AC, which by definition IS hum.
 






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