Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on March 07, 2011, 07:35:00 pm
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When I do my heater wiring, previously I have gone to great trouble from PT taps to last V1 preamp tube to keep the twisted wires seperate to maintain continuity with the identical pin # through the power tubes all the way to the last preamp. In other words like on a 5E3 the same continuous connection for one side 6V6 Pin #7, other 6V6 Pin #7, 12AX7 PI Pin # 4 & 5 and 12AY7 Pre Pin#4 & 5 and on the other 6V6 pin # 2, other 6V6 Pin #2, 12AX7 PI Pin #9 and 12AY7 Pre Pin #9.
I was told today that that was unnecessary. So before I drop this proceedure please verify that it is unnecessary. :undecided: Platefire
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I've been reading a lot of people say it's unnecessary too so I'm interested.
I have also read and seen videos where people say it is very important. Personally, I think it's very easy and can do no harm so I will keep doing it that way.
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http://www.el34world.com/charts/fenderservice4.htm <--- that guy thinks it's important that the power tubes are in phase. :grin: I certainly don't know enough to say one way or the other, but it does "make sense" that they're wired in phase.
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I've never found it to matter. Layout and grounding are much more important. I also used to wire from the xfmr, to the pilot light, to the output tubes, to the PI, and ending at V1. I'm not even certain that matters. I did a split chassis that ended at the pilot light. What does matter is keeping those dirty wires away from the grids. I'd be more inclined to go to DC filaments before worrying about AC polarity.
That's my $0.02
-Richard
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It's not necessary. Looks good though, so don't stop. The girls that worked for Leo didn't care. Nor did the QC people. Look at this original '64 Deluxe Reverb. See what I mean...
http://home.comcast.net/~seluckey/dr01.jpg
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Thanks
Looking at the picture, we try to do our boards and wiring so picture perfect, they sure wasn't worried about that! I got to where I burn all my cloth wiring ends off because I can't stand those fuzzed up ends.
I guess on the heater wiring if you have got it properly grounded, as long as each heater pin gets its 3.15 ACV, it doesn't matter where it comes from!
And like you say, I'll probably keep doing my method because it makes me feel good about it! Platefire
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I've always used 2 colors to wire my heaters, usually green and white, so it's pretty easy to keep them in phase.
Whether it lessens heater hum or not I do not know.
BUT I've learned over the years that working and building things in a consistent manor helps me to see things a little clearer, I like orange wires to my plates, blue wires to the grids and brown to the cathode. and I add a stripe with a black sharpie for the pin 678 side of my twin triodes.
Even if it doesn't help to reduce hum, I think the effort to be orderly will pay off in the long run.
Just the opinion of a less than stellar amp builder,
Ray
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I've never found it to matter. Layout and grounding are much more important. I also used to wire from the xfmr, to the pilot light, to the output tubes, to the PI, and ending at V1. I'm not even certain that matters. I did a split chassis that ended at the pilot light. What does matter is keeping those dirty wires away from the grids. I'd be more inclined to go to DC filaments before worrying about AC polarity.
That's my $0.02
-Richard
I can't imagine how heating the filament one way or the other would matte. I have never noticed a difference.
Butterylicious-I think your order is good and does matter. As you work to the more sensitive stages you have less and less current in the heater wires. By the time you get to V1 you have the least current possible AC heater current & it's less likely to induce noise.
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That is exactly my reasoning, to keep all that dirty current away from V1. On a couple of amps, it has worked out where I was able to "T" off at the pilot light and send 1 pair to the outputs and PI, and the other pair to the preamp tubes. It's just how the layout worked best.
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Let's try to reason this through.
Power amp. The input signal is rather large. I think the mu of a power tube is small, so hum and noise are not big issues. This is because heater hum doesn't get much amplification, and is weak compared to signal strength. Hum and noise in the power amp does not get re-amplified by later stages. Finally in a PP power amp, hum and noise get canceled-out. But in an SE power amp with 2 or more power tubes, maybe heater hum would be a factor? Any experiences here?
Pre-amp. Here hum & noise get re-amplified, the more so if it starts in early stages. With a balanced, ground-referenced heater supply, the heater of ea tube (assuming 12a_7) gets about 3VAC on each side, out of phase, for internal hum cancellation. In the real world, the balance of the heater supply, and thus hum cancellation, will be imperfect. So we're stuck with some heater hum. Let's say that the 2nd preamp tube has its heaters wired in reverse from the first tube. How & why would this affect the increase, if any, of the amplitude of heater hum in the signal path?
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I can't see how the polarity would matter, I do however believe the should be twisted to reduce induced noise. The only way routing (which tube or pilot is hit first) would matter is from a purely electrical stand point , as a electrician , when you wire in your panel you put the largest load at the top of the panel , you do this to prevent lights from flickering when the larger load is applied.
Rock On
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> as a electrician, when you wire in your panel you put the largest load at the top of the panel, you do this to prevent lights from flickering when the larger load is applied.
?? Should not matter.
Certainly not here. I have 400 feet #2 wire from the street, then one foot of fusebox bus comparable to #0 or fatter. Even if I had only 50 feet #0 wire from street, another foot down the bus would be hardly any different. The "flicker" drop is in the long wire, not the short bus.
> say that the 2nd preamp tube has its heaters wired in reverse from the first tube. How & why would this affect the increase, if any, of the amplitude of heater hum in the signal path?
Insufficient data. What is the gain/loss between V1 and V2?
In general: in a gitar amp there will be adjustable gain/loss scattered around V1 V2. While in theory a specific heater unbalance "might" cancel for one specific knobs-setting, it will not cancel for any other knobs-settings.
You can hear this in Ampeg VT-40 PCB amps. The heater lines on the PCB do not field-cancel like twisted wiring tries to do. There is a "hum balance" trim to offset the "center"-tap to match the PCB route unbalance. You can trim it for lower hum.... but then you change a volume or bass knob and the hum comes right back.
No. heater-phase does not matter electrically. It may look better with all the green on left and all yellow on right of each socket. But the main idea is: if you put your eye on a grid or plate pin, and squint, the heater wires should look equally yellow-green, not mostly-green nor mostly-yellow. That means the pin will "feel" both sides equally, and (if center-tap balanced) will feel "no" hum.
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The only way routing (which tube or pilot is hit first) would matter is from a purely electrical stand point , as a electrician , when you wire in your panel you put the largest load at the top of the panel , you do this to prevent lights from flickering when the larger load is applied.
Since the strength of the magnetic field near the wiring is proportional the the current flowing in the wire, I believe the routing is an issue. The current through the filaments will be the same for like tubes. However, the current in the wiring near the tube sockets will be greater in the early part of the parallel run. So I like to have V1 in the last part of the run & power tubes first in the run.
I've seen a nice diagram of this concept in one of Merlin Blencowe's books & it is much more clear than my description.
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While in theory a specific heater unbalance "might" cancel for one specific knobs-setting, it will not cancel for any other knobs-settings.
I don't get heater "balance". I know that adding the 100 ohm resistors to create a "balanced CT" for a non CT transformer often works for me but I don't know why. Can you (or anyone else) explain?
Thanks.
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>?? Should not matter.
Agreed but what Jack described is a standard practice. Panels dress out better with all the larger conductors grouped closest to the feeders. Everything is parallel connected to the bus. If the bus and feeders are adequate, then there shouldn't be any flickering when an air conditioner kicks in, but unfortunately in the dead of summer when the entire electrical grid is taxed, start up surges will momentarily drop the voltage. It doesn't matter where you tap your lighting circuit under this condition. If I add a 50 amp circuit for something to an existing system, I won't shuffle all the 20 amp breakers to put the new load closer to the feeder, but in a new build I will circuit my panel as described.
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While in theory a specific heater unbalance "might" cancel for one specific knobs-setting, it will not cancel for any other knobs-settings.
I don't get heater "balance". I know that adding the 100 ohm resistors to create a "balanced CT" for a non CT transformer often works for me but I don't know why. Can you (or anyone else) explain? Thanks.
There are 2 ways to supply, say, 6VAC to a tube's filament:
1. Unbalanced: 6VAC to one side, and -0- VAC to the other side. This is an unbalanced supply and does not have humbucking.
2. Balanced: 3VAC to each side. The two supply wires carry out of phase 60Hz AC. In an ideal world, when combined the 2X 3VAC adds up to 6VAC and cancels out 50% of the 60Hz hum. (By joining pins 4&5 with 9 on a 12a_7 tube, the internal heaters are wired in series so voltage doubles agains to 12VAC). To get the balanced supply you need either a) a 3-0-3 CT tranny; or b) a two-wire 6-0 tranny with an artificial CT that forces it to behave like a 3-0-3 tranny. Note that a CT is never perfectly centered. So you can get more perfection from an artificial CT using precision or matched fixed resistors, or an adjustable pot.
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(By joining pins 4&5 with 9 on a 12a_7 tube, the internal heaters are wired in series so voltage doubles agains to 12VAC).
Say what? :huh:
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" There are 2 ways to supply, say, 6VAC to a tube's filament:
1. Unbalanced: 6VAC to one side, and -0- VAC to the other side. This is an unbalanced supply and does not have humbucking.
2. Balanced: 3VAC to each side. The two supply wires carry out of phase 60Hz AC. In an ideal world, when combined the 2X 3VAC adds up to 6VAC and cancels out 50% of the 60Hz hum. (By joining pins 4&5 with 9 on a 12a_7 tube, the internal heaters are wired in series so voltage doubles agains to 12VAC). To get the balanced supply you need either a) a 3-0-3 CT tranny; or b) a two-wire 6-0 tranny with an artificial CT that forces it to behave like a 3-0-3 tranny. Note that a CT is never perfectly centered. So you can get more perfection from an artificial CT using precision or matched fixed resistors, or an adjustable pot. "
Thanks jjasilli! That makes sense.
If you have a 12v filament transformer available, you can use pins 4 & 5 in series (without connecting anything to pin 9), and have half the current running through the wires. This may lessen the noise also.
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(By joining pins 4&5 with 9 on a 12a_7 tube, the internal heaters are wired in series so voltage doubles agains to 12VAC).
Say what? :huh:
He means parallel.
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long live dyslexia!