Heater Wire Ground

[R.G.]

actually power rheostat 5W is the best, but R.G. is stating that we need veery precise resistors, lets hear from him why.

You're trying to put words in my mouth again. What I actually said was:

(1) And the heater center taps are sometimes not too accurate. A couple of resistors may well make a better center tap, with lower induced hum.

What part of "sometimes not too accurate" and "may well make a better center tap" did you misunderstand?
I see neither "veery" nor "precise" in there.
If you read the measurements and technical reference reply, you could have gotten a little understanding of why heater windings are not always accurate and by how much. Does it happen on every transformer? Nope, didn't say that. Yet it can happen, and in that way, and I've seen it, and found that resistors, even imprecise ones, can get you closer to balanced.

This brings up the issue of how balanced is enough. If you have an amp that leaks some AC current, you can - crudely, at least - buck out some of the hum by using a resistor network to imbalance the heater voltages in a way that cancels it to some degree. That is, in fact, the idea behind the "humdinger" hum balancer setup. Have you ever seen one of those?

[pdf64]

(1) And the heater center taps are sometimes not too accurate. A couple of resistors may well make a better center tap, with lower induced hum.

Why do you think that the minimum hum is on the middle of very- too much precision- resistors ? Give us some technical reference and measurement.

I've no citation or measurement sorry, but to me, it seems a given that the better the balance between opposing polarity currents being carried by a twisted pair, the better the cancellation of the radiated EM fields will be.
Hence the 'less induced hum' statement seems reasonable.

However, I cant see that the accuracy of the balance will affect buzz etc due to leaky h-k insulation within early stage valves.
Heater DC elevation is good simple mitigation for that.

[R.G.]

It's not for the actual heater currents. It's in case the CT is grounded and one heater wire breaks or otherwise gets shorted to the chassis or signal ground.

I've been doing this stuff since '65 and have never witnessed such a failure. Have you? This just sounds like one of those new age theoretical exercises where you fuse everything just because it 'may' happen. In reality you can be over cautious to the point where the fuse becomes more of a liability than the circuit it was meant to protect.

.
I hit tube equipment in about '68. I have seen one incident, in an expensive bit of military kit at school in '70.
Does it happen often? No.
Can it overheat/burn a PT if it does happen? Yes.
Is it worth the added expense and time to put protection in? Deep question.
The heart of it is - what is worth protecting, and will/can you get away with not protecting it? Half-heater shorts are rare. Not even all of them will kill the PT. So yeah, it could be more trouble than it's worth. I've been driving since '66. Never needed a seat belt, even back when there weren't seat belts.
And you are right - it is a balancing act between the cost of the protection, the cumbersomeness of having the protection (we all hated and laughed at seat belts when they were forced on us), and the cost of replacing whatever might get lost. If a PT is easily and cheaply replaceable, sure, why bother with fuses? If a PT is thought of as an irreplaceable "original" and maybe especially if someone thinks it is a valuable part of their "tone", it might make sense to worry about protecting.
It's a balancing act. Some people like suspenders and a belt. Some are happy to base-jump.

[sluckey]

I just think about the millions of top name amps that never fused the filaments. And I also remember the first new car I bought in the '60s... lap seat belts were optional, and you had to pay extra!

[R.G.]

I just think about the millions of top name amps that never fused the filaments.

You're right about that. In fact, even the military (per my experience) didn't. It depends on your objectives. If you want to prevent certain losses, there are often technical ways to do that. If you're OK with sustaining the infrequent loss (the insurance biz calls this "self insuring") it's fine to skip the prevention.

To a manufacturer, an amp that runs way beyond warranty is a problem, not an advantage. I have heard rumors that the insiders at what passes for Fender these days views their major competitor to be their decades-old amps. The MBA holds that products failing and wearing out is a good thing, viewed the right way. So yeah, millions of amps never put in transformer fuses. Why add the cost when we want repeat customers, and we think most of the PTs will get past warranty?

I got on this buzz a few years ago when I wondered whether it was possible to mitigate against predictable losses in tube amps. I had this concept of the "immortal amplifier". They're pretty good already, as witness the '50s and '60s that still exist. But we know that over time, the electrolytics are going to rot. Tubes will fail - that's why they're in sockets. But there might be ways to minimize the damage. Tubes fail. OK. But if a tube fails in a way that takes out the PT or OT, that's another thing entirely. We used to do an engineering exercise back at work where we took the costed bill of materials for a product, and sorted by highest cost first. Doing this on a guitar amp usually turns up the enclosure first, in competition with the PT and OT. An &deity forbid some cheap thing racks up high warranty labor costs.

[bepone]

That's not bad for the high voltage windings, as a turn more or less doesn't make as big a proportion of voltage on the winding. But on heaters, half turns can matter.
Example: say you have picked a core which needs two turns per volt on the primary to keep the magnetizing inductance high enough and hence the magnetizing current low enough. If you're trying to make 6.3V... oops, you can pick 12, 13, or 14 turns for it. 12 turns gets you 6V, 13 gets you 6.5V, and 14 gets you 7V.

There is no half turn in transformer heater winding
For heaters you need to make very low number of the turns, and all the time you start and finish the turn on the same place..also is easy to make 3.15-0-3.15 , you are winding actually full number very close to the voltage (not to decimal point) actually it is 3.3-0-3.3 if you count losses with full current draw..
And there are in the same line, and winding geometry is the same, so it is the voltage..

But all of this doesnt matter because minimum hum is not on the half

[bepone]

I've no citation or measurement sorry, but to me, it seems a given that the better the balance between opposing polarity currents being carried by a twisted pair, the better the cancellation of the radiated EM fields will be.
Hence the 'less induced hum' statement seems reasonable.

However, I cant see that the accuracy of the balance will affect buzz etc due to leaky h-k insulation within early stage valves.
Heater DC elevation is good simple mitigation for that.

ok for the lifted heaters.. but with humdinger pot you can see that hum is depending of the heater construction in the tubes and for all the preamp, mixed tubes is variable.. you can see where is minimum on the turn

[wpaulvogel]

When winding a transformer the lowest voltage winding sets the ratio of primary to secondary. Yes we want the 6.3 volt and 5.0 volt windings to be 100% correct at loaded output of 5.0 volts and 6.3 volts but the tolerance of the tubes is enough that perfection isn’t critical. My transformers actually come in at about 2% accuracy and I’m excited about this. 11 turns for 5.0 volt and 14 turns for 6.3 on 256 turns 120 volt primary is perfect when loaded. It’s easy to adjust the HT secondary to get your projected voltage because the number of turns required to get the high voltage is at least 2-3 times the primary. Heater balance is important but the low level noise produced by the heater circuit is minimal and usually only relevant when the amp idles with volume controls set to 0. If you’re hearing heater hum at any other time than that, the problem is most likely in lead dress, grounding or you need a different transformer supplier. Heater hum isn’t a problem over here and I don’t do anything special with wiring it. Fusing is a good idea but I don’t do it. Maybe I should but I’ve never burned a winding after a completed build.

[R.G.]

There is no half turn in transformer heater winding
For heaters you need to make very low number of the turns, and all the time you start and finish the turn on the same place..also is easy to make 3.15-0-3.15 , you are winding actually full number very close to the voltage (not to decimal point) actually it is 3.3-0-3.3 if you count losses with full current draw..
And there are in the same line, and winding geometry is the same, so it is the voltage..

I can see that you just didn't understand what I wrote. Try reading it again. If you want me to re-write it in simpler language, I will give that a go. Other than not understanding my post, I can't see why you would try to say say back to me what I said, and try to imply that it's wrong, but when you say it, it's right. That's just weird.

You got the first part right - as I said originally, it's a low number of turns. But you missed several of the points on turns, or perhaps misinterpreted what I wrote.

I have both made the mistake myself and seen others make the mistake of not starting and finishing a full turn. In an E-I winding, it's possible to go through one window and not the other. This causes an unbalanced flux on the core. It is possible to take a center tap out halfway around the core and not unbalance the magnetic flux in the special case of both sections of the winding being equally loaded and low current in the tap without unbalancing the core flux. As I pointed out, there are reasons not to do this.
You missed the point on volts per turn. Volts per turn is fixed. With a low number of turns, you practically only have the option to get the closest number - I kind of think that's what you're trying to say here. In fact, if you actually read what I wrote, I went through an example of picking the nearest higher number of turns, and referenced the losses due to high current.

You are also skipping over the possibility of the winder making a mistake and simply putting one more turn on one of the halves of the heater winding. This can't happen with bifiar winding - which no one does for heaters - but it can, and has happened with two separate windings wound one after the other to make a "center tapped" winding. It doesn't happen much any more with commercial power transformers wound on automated equipment, but it can and does happen on hand wound stuff, including commercial transformers from back in the days when the winding machines were manually controlled. I have both measured what is probably a one-turn error in commercial transformers, and accidentally made the mistake myself when I was learning to wind them.

But all of this doesnt matter because minimum hum is not on the half

Hmmm. Are you trying to say that minimum hum is >never< when the heaters are exactly balanced, or just trying to start an argument?

Hum comes from lots of causes, as you should know. Even with pure DC heaters, there is still hum. I pointed out why an adjuster pot lets you use offset heater hum to cancel out hum from other sources to some extent. Did you not read that part of my post, or not understand it?

[R.G.]

ok for the lifted heaters.. but with humdinger pot you can see that hum is depending of the heater construction in the tubes and for all the preamp, mixed tubes is variable.. you can see where is minimum on the turn

That is, you're re-stating what I said: hum comes from lots of places, and you can use a resistor setup to cancel some of the other sources.

[bepone]

R.G. it is almost impossible to wind differently heater winding halves, how did you manage to make that? if you want centre tap, it will be exactly on the centre

[bepone]

just a note for you because youre spending too much words for nothing i wound maybe several hundreds pts in my life and projected another several hundred ..

[R.G.]

R.G. it is almost impossible to wind differently heater winding halves, how did you manage to make that? if you want centre tap, it will be exactly on the centre

bepone, it's an easy mistake to make. I've both done it on my earliest winds, and seen other beginners do it when they're learning. I've seen experienced winders do it when they're bored. It's not almost impossible; your experience is not universal.

[R.G.]

just a note for you because youre spending too much words for nothing i wound maybe several hundreds pts in my life and projected another several hundred ..

And as a note for you, you are wasting your time and words too.

You''re back to the argument that "well, I've seen this, and therefore, that's all that exists." I've designed transformers from the equations on up through winding design and then hand fabricated prototypes that were then put into production for commercial products, for both line frequency and high frequency switching transformers. I suppose it's possible you've done something similar, but your posts don't display that kind of background.

And it's particularly telling that you echo back to me what I just posted, and try to use that to say I'm wrong. Sad, really.

[R.G.]

@ Magnatron: Sorry for the flurry from bepone. It can get confusing when people get off into bickering over minutae. That little back and forth didn't help you much, I think.

Did you get anything useful to answer your question?