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#1
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
The thread title says it all. Hot referring to DHTs of course !
Obviously capacitance plays its part but is there another mechanism at play ? Graham |
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#2
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
On Mar 2, 9:57 am, Eeyore
wrote: The thread title says it all. Hot referring to DHTs of course ! Obviously capacitance plays its part but is there another mechanism at play ? Graham Some general points: 1. Yes, capacitive coupling from the heater to other tube elements is certainly a source of hum. 2. Another in-tube source you do not mention: heater-cathode leakage 3. Another in-tube source you do not mention: heater-cathode emission 4. Another in-tube source you do not mention: the 60Hz magnetic field of the heater modulating/steering the electron flow 5. An out of tube source you do not mention: capacitive coupling from heater wiring under chassis to any high-impedance low-level circuit 6. An out of tube source you do not mention: inductive coupling from heater wiring or filament transformer field to any circuit loop. This can be very insidious because altering layout to remove large-area loops is something that has to be dealt with at design-layout time and is impossible to correct later. 7. Finally there are lots of ways that hum in any power supply could find its way to amplifier output. Tim. |
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#3
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
Hi RATs!
DHT's have no heater-cathode issues ... Some basic premises used in retail amplifier design are not the result of careful design critique, simply quick and dirty ways to get a product out the door and sucking in ill-gotten revenue. I am responding to my medications for a long term sinus infection and feel glee at being able to rant, so: Enjoy! 1. One box is all any amp needs. This is real smart, huh? Power transformers, rectifiers and filter networks really need to be real close to amplifier circuits, because ... it is cheaper! No good reason. Just bean counter power trips. 2. Heaters need to be heated with unfiltered AC, because ... it is cheaper! No good reason. Beans, again ... 3. Heater circuits do not need to be shielded, because ... it is cheaper ... 4. Heater circuits need to be in parallel strings, because ... can you guess? 5. Heaters do not need their own transformers, rectifiers and filter networks, because ... you ought to know by now ... I do not think it is impossible to enjoy music played through a cheap, one box solution. I do think pretending cheap, one box solutions are the only possible design worth considering is a bit silly. Cheap and smart are not synonyms. Only cheap people assume they must be  Smart people look at the evidence, not the bottom line You may get rich, but you can still be stupid ... Happy Ears! Al |
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#4
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
On Mar 2, 12:34 pm, "tubegarden" wrote:
2. Heaters need to be heated with unfiltered AC, because ... it is cheaper! No good reason. Beans, again ... 5. Heaters do not need their own transformers, rectifiers and filter networks, because ... you ought to know by now ... At the same time, having a high-current (several amps) DC filament power supply means that you've got filter capacitors drinking large chunks of current in gulps that are several times larger than the average current. This means a lot of harmonics spiking 60 or 120 times a second, and the OP's point about capacitive coupling is even more relevant to the higher frequency harmonics being generated, because the higher frequencies get more capacitve coupling. Sometimes a clean 60Hz sine wave is truly the right thing to power your filaments with. Simplicity has its benefits and making your power supply more complicated than your amp is surprisingly uninteresting to me! At the same time, getting clean 60Hz out of a wall socket or transformer may prove to be more difficult for some than others :-) Tim. |
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#5
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
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#6
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
In article .com,
wrote: 6. An out of tube source you do not mention: inductive coupling from heater wiring or filament transformer field to any circuit loop. This can be very insidious because altering layout to remove large-area loops is something that has to be dealt with at design-layout time and is impossible to correct later. Can you elaborate on why you say this "is impossible to correct later"? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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#7
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
On Mar 2, 2:24 pm, John Byrns wrote:
In article .com, wrote: 6. An out of tube source you do not mention: inductive coupling from heater wiring or filament transformer field to any circuit loop. This can be very insidious because altering layout to remove large-area loops is something that has to be dealt with at design-layout time and is impossible to correct later. Can you elaborate on why you say this "is impossible to correct later"? If you've laid out the tubes/sockets/transformers to form such a loop, and the loop has a large area, it's nearly impossible to add magnetic shielding to remedy the problem. You pretty much have to start over punching new holes in a new chassis. Same thing happens with magnetic fields and poorly-laid-out solid- state amps (although these do not have filament supplies they still, if AC-powered, have a transformer and in fact larger pulsating 60/120Hz currents). In case you haven't read between the lines: all the above learned from the school of hard knocks, a couple decades ago for me! It's very disappointing to find out that there is NO practical fix to the inductive-loop susceptibility other than starting over. Contrast with capacitive coupling where you can start band-aiding via electrostatic shields etc. Tim. |
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#9
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
On Mar 2, 3:05 pm, John Byrns wrote:
In article om, I don't understand why one can't avoid large area loops in the heater wiring by simply insuring that both wires feeding the heater of any given tube are placed in close proximity to each other, preferably twisted, eliminating any large area loop? The loop I was talking about was not the heater wiring (you're 100% right, run this in twisted pairs and the hum from their loop mostly cancels out) but the susceptibility in loops in non-heater circuitry to 60Hz from power transformers and chokes. The 60Hz transformers (including the heater transformer but also the other ones) on the chassis or even nearby chassis have a pretty good- sized near-field. Make a signal loop in that near-field and you'll pick up hum. One workaround that I neglected to mention, which isn't practical in every case but not as impossible as I was saying!, is toroidal power transformers which will have less field. But it's still better to not have the susceptibility from the get-go. A good sign of a design susceptible to magnetic interference is that they have applied the band-aid of toroidal power transformers :-). Tim. |
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#10
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
5. Heaters do not need their own transformers, rectifiers and filter networks, because ... you ought to know by now ... I do not think it is impossible to enjoy music played through a cheap, one box solution. I do think pretending cheap, one box solutions are the only possible design worth considering is a bit silly. Cheap and smart are not synonyms. Of course bean counting impacts the design. Really smart engineers know how to get great quality from limited budgets. Twisted heater wiring is done to reduce magnetic and electrostatic hum fields. Some amps with preamps use the preamp tube heaters as cathode resistors for the output tubes as an easy and cheap way to get DC heater current for the preamp tube heaters. And they save money they would have to spend on power resistors. Oh, you'll need a bypass electrolytic to keep audio from the output tube from feeding back into the preamp, put that in the "downside" column. And so on. Experienced designers know where they can cut corners and what needs attention. |
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#11
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
On Mar 2, 11:05?am, wrote:
Sometimes a clean 60Hz sine wave is truly the right thing to power your filaments with. Simplicity has its benefits and making your power supply more complicated than your amp is surprisingly uninteresting to me! At the same time, getting clean 60Hz out of a wall socket or transformer may prove to be more difficult for some than others :-) Tim. Hi RATs! Simplicity is wonderful, when it works. The OP was just feeding chum to the sharks, or tadpoles, whatever Making anything more complicated is boring to me, too. Trying to fool consumers is a great hobby, but, so is listening to recordings. If something does not function as you wish, you may modify it until it does. Or, until you die Multiple power transformers are not "more complicated" than one with multiple taps. They just take up more space. Even the SS guys should be able to comprehend that concept I modify stuff for the thrill of physical activity in this rather strange time/space thing. Sometimes I am mortified by failure, once in a while my soul shines brightly. It is a crap shoot Happy Ears! Al PS First rule: No Rules! PPS "Clean" 60 Hz? What planet are you on? |
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#12
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
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#13
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
tubegarden wrote: Hi RATs! DHT's have no heater-cathode issues ... Idiot ! Graham |
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#14
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
John Byrns wrote: wrote: 6. An out of tube source you do not mention: inductive coupling from heater wiring or filament transformer field to any circuit loop. This can be very insidious because altering layout to remove large-area loops is something that has to be dealt with at design-layout time and is impossible to correct later. Can you elaborate on why you say this "is impossible to correct later"? Run the heaters on DC ! Graham |
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#15
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
In article ,
Eeyore wrote: John Byrns wrote: wrote: 6. An out of tube source you do not mention: inductive coupling from heater wiring or filament transformer field to any circuit loop. This can be very insidious because altering layout to remove large-area loops is something that has to be dealt with at design-layout time and is impossible to correct later. Can you elaborate on why you say this "is impossible to correct later"? Run the heaters on DC ! That won't help because the actual problem he was talking about is the field from the power transformer being picked up in the signal wiring. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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#16
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
On Mar 3, 9:43?am, Eeyore
wrote: Idiot ! Graham Hi RATs! Always happy to share the sunshine of tube love with the truly desperate denizens of the Dark Future  Happy Ears! Al |
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#17
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
On Mar 3, 9:42?am, Eeyore
wrote: I know. I was specifically interested in the heater aspect inside the tube alone in isolation. Hi RATs! Some people are so pithy no one can understand them. At least they don't waste too much of our time ... Happy Ears! Al |
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#18
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
John Byrns wrote: Eeyore wrote: John Byrns wrote: wrote: 6. An out of tube source you do not mention: inductive coupling from heater wiring or filament transformer field to any circuit loop. This can be very insidious because altering layout to remove large-area loops is something that has to be dealt with at design-layout time and is impossible to correct later. Can you elaborate on why you say this "is impossible to correct later"? Run the heaters on DC ! That won't help because the actual problem he was talking about is the field from the power transformer being picked up in the signal wiring. No he was talking about the radiated field from the AC heater wiring ! Stray field from the power transformer is quite another issue. Do please try to keep up ! Graham |
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#19
Posted to rec.audio.tubes
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Is hum from the heater circuit capacitively coupled ?
In article ,
Eeyore wrote: John Byrns wrote: Eeyore wrote: John Byrns wrote: wrote: 6. An out of tube source you do not mention: inductive coupling from heater wiring or filament transformer field to any circuit loop. This can be very insidious because altering layout to remove large-area loops is something that has to be dealt with at design-layout time and is impossible to correct later. Can you elaborate on why you say this "is impossible to correct later"? Run the heaters on DC ! That won't help because the actual problem he was talking about is the field from the power transformer being picked up in the signal wiring. No he was talking about the radiated field from the AC heater wiring ! Stray field from the power transformer is quite another issue. Do please try to keep up ! Oh floppy eared one, I suggest it is you who are not keeping up! This thread has more than one branch, and if you read them all my comment should make perfect sense to you. To make it easy for you I will quote what he actually said that I was referring to. "The loop I was talking about was not the heater wiring (you're 100% right, run this in twisted pairs and the hum from their loop mostly cancels out) but the susceptibility in loops in non-heater circuitry to 60Hz from power transformers and chokes." "The 60Hz transformers (including the heater transformer but also the other ones) on the chassis or even nearby chassis have a pretty good- sized near-field. Make a signal loop in that near-field and you'll pick up hum." If you are going to start a thread you would do well to read all the responses before putting your foot in your mouth. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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