Heater Wire Question


Not So Mediocre Member
I'm planning out my SET amp build. A question I have is there any value in shielding the heater wires? I'm not worried about EMI effecting the heaters but the opposite. Would passing the heater wires through some grounded copper braid help to reduce the potential for noise? I know about tightly twisting the leads as well as running the wires along the sides and deep into the corners.
Are you talking about the output tube filaments or driver stage heaters?

Output tube heater wiring will be raised above ground by the bias voltage if self-biased. This will reduce hum field radiation greatly.

Now, the driver tube heater wiring, if AC, should also be biased relative to ground for the same reason, particularly since SE amps will not cancel hum.

Pick 20V or so off of the B+ supply through a voltage divider and elevate the heater wiring above ground instead of shielding it.

Watch the heater to cathode voltage rating of the driver tube(s), but 15-20V should be OK for any tube.
Joe, elevating the heater supply for your driver tube might reduce hum (not necessary in any of my amps) but it can also affect the sound quality. Each time I have done an A/B comparison of elevated vs direct ground reference, I have preferred the sound quality of the grounded heater supply. Of course if you need an elevated supply due to heater-cathode voltage, that’s another story, but for all other situations I prefer the grounded supply.
Maybe you're right, but it is hard to come up with an explanation for your findings. Do you have one?

Did you measure more hum with the non elevated heater line or not? If you have any induced hum, this would seem to negate any improvement thanks to directly grounded heaters, although I wonder whether a small, generally imperceptible level of hum might not lend a certain positive character to the sound?

Also, as mentioned above, a self biased directly heated output tube will have an elevated heater line anyway, so that curse remains.

For a novice constructor who would even ask the OPs question, I say elevate the heater line. One could use shielded twin conductor for the heater line, but I never had to resort to that. Shielded signal input wiring to the first tube might not be a bad idea though.

A hum balance pot may or may not be adequate to reduce hum, depending on the specific build, tubes etc. I used to do it all the time, then switched to a few volts bias on the heater wiring as standard practice.
I don’t have any measurements or a technical explanation for why the grounded heater supply sounds better. My meter doesn’t have a “Sounds Better” setting.

As for hum, I have to use my 46 SE amps as a test bed because my PP amps are all dead quiet even with AC heaters throughout. My 46 amps are also AC heated for both the 46 outout and the 417a input/driver, and they do have a very slight hum over my 98 dB sensitivity speakers. I can hear the hum when there is no music playing and I am within a foot of the speakers, but I can’t hear it at all if I am further away. That low hum is due to the 46 outputs so if the AC heater supply for the input tube is adding any hum I wouldn’t know it. But as I said my PP amps don’t have any audible hum and they have AC heaters on the input tubes.
My meter doesn’t have a “Sounds Better” setting.

Yuk, yuk.

As you may know, I am a staunch critic of the kind of naive objectivism that passes for knowledge and wisdom on some forums.

i approach these questions as an anthropologist, specializing in philosophy of science and social construction of knowledge systems, although I usually only switch into that mode online when confronted with arrogant fools overstepping the boundaries of their understanding.

In academic philosophy, a very useful distinction to be made between knowing that and knowing how. Most of our practical knowledge is of the knowing that variety. We only have to know what things do in order to use them, rather than understanding how they do it in great explanatory detail. Even in science, many things are not fully understood but if there is predictability, then we can use it.

An example is cathode physics. There is a book on the oxide coated cathode, written in the late 50s, at the end of the tube era by a British professor. Paraphrasing, the first sentence of the book is along the lines of "The mechanism of the oxide coated cathode is not fully understood." The fact that there were competing models for the cathode action and no resolution did not seem to hamper the manufacture of billions of tubes up until that point! A few years later, nobody cared anymore. No grant money in it.

I recognize it as perfectly valid knowledge to recognize that something happens even if there is no handy empirical explanation for it.

Yet, concerned as I am with understanding the audio experience, even if valid technical explanations can be hard to muster, there must be some experiential sonic correlate of the implementation that we are singling out to prefer.

I 'm progressively more lazy now but I used to build and do meticulous experiments all day long. I've heard a lot of hum.

My current position on this, conditioned by ten years of working with super, super quiet tube gear on speakers up to 115 dB speakers, is a new working theory on what hum might do.

First reaction to really quiet, very very low distortion, all direct coupled tube gear is that it might sound a little boring compared to the 1930s/1940s style DIY projects I liked to build with oil caps and whatnot.

Really, after learning the results of this sort of program, where everything is optimized on Audio Precision gear and built using the best possible parts and tubes, DC supplies and double regulated B+ with impedance optimized capacitance multiplier decoupling everywhere, I have to say that it is far higher resolution than the usual run of old school tube amps, far wider dynamic range, much better presentation of complex musical signals.

Still, to me, a little something is missing from my modest home builds, aside from affordability.

What is missing might be hum modulation, which on an non-intrusive level might have positive characteristics, in the same way a bit of vibrato or tremolo enhances the emotional impact of a tenor's voice and electric guitar....any instrument really.

In other words, what is an electronics problem, might not be so much a problem for listening, even for some very experienced listeners. In fact, it might sound better in certain ways!

In any case, listening creates its own universe of truths for each listener. Often this will exceed our capabilities to explain what we think we know about what we're hearing. We can leave it right there and just do it.

Or, in the quest for better understanding of ourselves and our art, we can try to at least try to come to grips with what in the audio musical experience we are responding to. There might not be easy explanations but there has to be something in the "signal" that is to some degree qualifiable if not easily quantifiable that we are responding to.

It is often difficult to talk about this sort of thing because we don't have language to describe subtle sonic effects. Usually metaphor is called into play, which is very tricky ground for analysis.

All this from the guy who introduced the term "psychedelic" into the review lexicon, right?

I believe that we can learn to understand what we are responding to, if not how it all works out on paper.

So, I disagree that your meter doesn't have a "Sounds Better" setting...it does and your meter is your brain.
Interesting ruminations Joe. I only have two comments.

First, I totally understand the quandary between knowing how and knowing that. I came to grips many years ago with the fact that I would never have satisfying scientific explanations for some of the sonic observations that I have had over the years. More importantly, I realized that trying to find scientific explanations for all experiential observations can result in blinders that cause one to become unable to appreciate true sonic differences. You won't hear a difference if you already "know" there can't be one. An easy example is wire. If you start with a scientific analysis and conclude that the only factors that could affect the "sound" of wire are resistance, capacitance and inductance, then you may talk yourself into a conclusion that all wire sounds the same provided these electrical properties do not have measurable effects in the audio range. Yet my ears tell me that analysis is wrong. Different types of wire can sound very different even when they are just a short link between two connections in an amplifier or two connections in a speaker crossover. I would rather approach my listening with an open mind and not wear blinders that prevent me from hearing all there is to hear. However, I also can't stand it when someone presumes to know why A sounds different from B based on analytical tools. For example, someone might say that the reason a 4.7uf cap has "more bass" than a 3.9uf is that the -3db point is a few tenths of a Hz lower when actually it is just the caps are different types.

Second, concerning hum, I had a real eye opening experience when I was using 300B SE amps which I built with AC on the heaters. The hum was annoying initially but I found that by changing the wiring layout I was able to reduce the hum significantly, not just once but several times as I tried different layouts. What I ended up with was a hum level that was much lower than when I started and mostly acceptable even on high efficiency speakers. When I switched over to the 46, I kept the same type of layout and the hum was then no longer a factor at all.
Wire is a classic example. RLC only blah blah blah.

Well, while in an argument with some EE pinhead on another forum, yeah about wire. I asked how his BA in EE actually qualifies him to say anything on the subject. After all, my partner at Silbatone has a PhD in solid state physics and electrical materials and he is the one ordering silver litz by the kilometer.

I went to Google scholar and did a few searches on keywords like "boundary+effects-copper" annealing stress conductivity copper" diamagnetic conductor paramagnetic conductor etc and found literally tens of thousands of scientific journal articles that looked beyond RLC in electrical conductors.

The dude didn't have a clue this vast world of scholarship on electrical materials existed. You know know what you don't know, as the old saying goes.

Fittingly, Dick Olsher just wrote a review of magnetic cables in Stereophile and it begins with a tirade based in philosophy of science, mirroring some of what we are talking about here! What are the chances that I would get that link in my box this afternoon?


Is this finally the time for audio community to catch up with the last 100+ years of intellectual history?

Enough of TV repairmen and guys who learned how to fix radios in the Navy lecturing the rest of us about SCIENCE.

I tell them that the logical postivism they espouse as scientific method was entirely discredited and abandoned by its main adherents, the Vienna Circle, before WWII, but I don't think they read any of the links I provided for further education on the topic.

Last edited:


Staff member
Fittingly, Dick Olsher just wrote a review of magnetic cables in Stereophile and it begins with a tirade based in philosophy of science, mirroring some of what we are talking about here! What are the chances that I would get that link in my box this afternoon?

I fully agree with everything in your post, but one point of clarification regarding the Dick Olsher piece, it's a reprint of an article originally appearing in Stereophile in February 1991.

I remember that piece well, and my local dealer actually had the Lindsay Geyer interconnect cable available for take-home demo in one's own system.
Actually to be honest, I only read the first few paragraphs! Once Olsher got past from the philosophical intro, my attention waned.

And here I thought we were on the verge of a major paradigm shift!

By 1991, I had long given up on high end mags and was trying to put together my own having nothing to do with high end audio, except to smash it. I was also not about to walk into a high end shop. I was totally fried on the upscale audio world after working in retail for a couple years, then started building all my own stuff, fixing up and surveying vintage gear, studying books and mags from the 40s and 50s. Went my own way.

I picked up a copy of the latest Stereophile at the DC Audiofest last year and I swear I read that exact issue in 1990 or so!:tongue:

They all look the same, read the same.

Isn't there somebody else hawking a new magnetic cable this year? I read about it somewhere but wasn't paying that much attention. Perhaps that's why JA reprinted the article?
Last edited:

Golden Gate ER

Senior Member
3 twist per inch is standard. All you really need to do is that and keep the wires tightly pushed up against the metal chassis and you wont have any problems.


Señor Member
I think a philosophy of science thread wouldn't be a bad thing.

I am saying that as a scientist who is (almost) as interested in the philosophy of the scientific method (and its implications, for better or for worse, in how "Western Man" formulates and tests hypotheses) as I am in the nuts and bolts of "doing science".

... I have done me some science in my time.
The problem is that once human aesthetic perception is involved, it isn't science anymore.

It is social science or human science...totally different knowledge conditions from the hard sciences.

In fact, as Olsher intimates, and the great weight of 20th century thought agrees, even the hard sciences are fundamentally sociocultural activity....because that is the only way people can apprehend and work in the world.

One big problem for audio forums is that almost all engineers never learned any of this stuff. They were too busy taking EE and math requirements to get a well rounded education in intellectual history in school.

I took all of the philosophy of science and philosophy of social science graduate classes offered at two major universities and I never saw an engineer in class. In fact, hardly anybody was in those classes, 3-6 students, and they were usually longhair philosophy students. Anthropologists, who really should know this stuff, are also woefully under-educated in this field. They also sometimes seem to have difficulties recognizing the limits of science but much of this problem has been purged due to rejection of logical positivist paradigms since the 1950s. It lingers here and there because this is what we all learned as "science" in high school.