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Old 23rd December 2012, 07:50 PM   #81
Bigun is online now Bigun  Canada
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Quote:
Originally Posted by Antoinel View Post
Electrons boil off the Wolfram wire, form a mobile sheath/cloud around it, and contribute to its classical solid state resistance. A hypothesis maybe that hot electrons may impart a "better" sound than cold ones meandering through a luke warm wirewound or Carbon composition power resistor.
I think you'd better lay off the egg nog :
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Old 23rd December 2012, 08:15 PM   #82
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Quote:
Originally Posted by Antoinel View Post
A hypothesis maybe that hot electrons may
impart a "better" sound than cold ones meandering through a luke warm
wirewound or Carbon composition power resistor.
The light bulb definitely imparts one characteristic - in the midrange the
filament has a resonance which creates a slight bump to the output.

Interestingly, many years ago I was puzzled to see a Julian Hirsch
(Stereo Review for you tadpoles among us) review in which the Levinson
ML-3 amplifier had a bump-up in the midrange. Now I realize that perhaps
they were trying to simulate the light bulb.

I like the lightbulbs. They are cheap and contribute an organic quality to the
whole enterprise.

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Old 23rd December 2012, 09:30 PM   #83
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Quote:
Originally Posted by Nelson Pass View Post
The light bulb definitely imparts one characteristic - in the midrange the
filament has a resonance which creates a slight bump to the output.

Interestingly, many years ago I was puzzled to see a Julian Hirsch
(Stereo Review for you tadpoles among us) review in which the Levinson
ML-3 amplifier had a bump-up in the midrange. Now I realize that perhaps
they were trying to simulate the light bulb.

I like the lightbulbs. They are cheap and contribute an organic quality to the
whole enterprise.

Thank you Mr. Pass for the information above, and thank you Bigun for responding. I'll have egg nog tomorrow. What if the incandescent light load [wrenchone's or that of Rothacher's V.1 SIT amp] is the filament of a vacuum tube; for example KT88? Its cathode heater uses 1.6 A, and the tube has a maximum plate current of 140 mA. In a next step, I am in a position to bias this tube normally [wrenchone's +45 Vdc is/maybe ground for tube]. Apply a grid signal that is either in and or out of phase with that at the amp's input. Will this hypothetical setup work, and further influence the sonics of the parent amp [tube not biased]?
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Old 23rd December 2012, 10:39 PM   #84
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I suppose it depends on the actual resistance of the heater. You are looking
for something on the order of 20 ohms.

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Old 24th December 2012, 12:35 AM   #85
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Quote:
Originally Posted by Nelson Pass View Post
I suppose it depends on the actual resistance of the heater. You are looking
for something on the order of 20 ohms.

Thank you Mr. Pass. The heater voltage for KT88 is 6.3V pushing 1.6 A. By contrast, the dual heaters in 12AX7 connected in parallel require 6.3 V which pushes ~ 0.3 A to give a heater resistance of ~20 Ohms. Will a signal on its grid or cathode modulate heater current; due to proximity; also noting that the maximum sum current of its plates add up to a meager 2.4 mA? If this is possible, then one has an Active and Functional incandescent load.
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Old 25th December 2012, 04:14 PM   #86
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I have been thinking about using tube heaters as well! I have a very very large pile of non usable for audio tubes that need uses!
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Old 25th December 2012, 05:17 PM   #87
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Quote:
Originally Posted by Zero Cool View Post
I have been thinking about using tube heaters as well! I have a very very large pile of non usable for audio tubes that need uses!
Lucky you; I only have four 12AX7s. I'll work with them this week and share the findings. Happy holidays.
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Old 27th December 2012, 11:16 PM   #88
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I checked out my hysteretic buck converter last weekend (I started up the circuit cold into a current source load and checked the inductor current vs. output voltage), and the performance (to me) was not acceptable. I basically want an ironclad current limit, but that's not happening, possibly because the hysteresis I'm programming is too small and the comparator is too slow. I have a possible solution for this, but before I discard the old design, I'd like to try a dodge where the programmed hysteresis is adaptive. In specific, I'd like to program a lot of hysteresis in cases where the input to output voltage difference is high - in other words, startup and overload/short circuit. In these cases, the output inductor of the regulator needs some time to discharge before the next switching cycle so that the output current doesn't ramp up out of control. I have a way to do this that I can hack into the existing circuit, and I might try it this weekend. It would be nice to get an acceptable solution with a crappy comparator like the LM393.

This is turning out to be interesting in the Chinese meaning of the term (may you live in interesting times...). There are no obvious single chip solutions I can apply to this problem, so it's up to me...
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Old 28th December 2012, 12:54 AM   #89
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Default This must be contagious

Quote:
Originally Posted by Zero Cool View Post
I have been thinking about using tube heaters as well!
I have been working on this for a few weeks. The diagram isn't labeled for parts values but the tube is a 12K5 space charge tetrode and the setup is very straightforward. The sound was very good I thought, but this one was dismantled and another constructed in its place utilizing a 15CW5 and MJ15003 with a single 30 volt supply. When biased for 1/2 supply at midpoint you get the requisite 300 ma through the filament (heater). The sound is very good (to me). I worried about crazy feedback and/or regeneration effects possibly showing up but I can't recognize any sonic problems with this. Apologies to Pete Millett and his "Starving Student" headphone circuit. This was not intended to be a ripoff, I was just curious one night and it happened to work, before I stumbled on his circuit. I was looking for something "hybrid" for a table radio project that is ongoing. There is hardly anything new under the sun. Just posted this to confirm it does work. And works well IMHO.

Cheers,
Terry
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Old 28th December 2012, 03:56 PM   #90
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Quote:
Originally Posted by Parasonic View Post
I have been working on this for a few weeks. The diagram isn't labeled for parts values but the tube is a 12K5 space charge tetrode and the setup is very straightforward. The sound was very good I thought, but this one was dismantled and another constructed in its place utilizing a 15CW5 and MJ15003 with a single 30 volt supply. When biased for 1/2 supply at midpoint you get the requisite 300 ma through the filament (heater). The sound is very good (to me). I worried about crazy feedback and/or regeneration effects possibly showing up but I can't recognize any sonic problems with this. Apologies to Pete Millett and his "Starving Student" headphone circuit. This was not intended to be a ripoff, I was just curious one night and it happened to work, before I stumbled on his circuit. I was looking for something "hybrid" for a table radio project that is ongoing. There is hardly anything new under the sun. Just posted this to confirm it does work. And works well IMHO.

Cheers,
Terry
Terry, It is contagious, and love the circuit you showed. I am also working on a circuit which I'll share ASAP. Kind regards.
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