I used LEDs as voltage references and bias elements in solid state designs in the early 1980s, and applied them to tubes considerably later, but before 2000. I also used and continue to use a variety of other diodes for bias. Never heard of the site you mentioned, have never made any claims to originality, and I think it's pretty likely that a lot of other people came up with the idea independently over time. (I'm also an EE)
you live a sheltered life.
https://courses.physics.illinois.ed...hall/R_Marshall_P498POM_Final_Report_Sp10.pdf
i use them exclusively on my SRPP layouts, Long tail pair, single diode bias for boot-strapped cathode follower stage, and along with para-feed drive for the power stages....
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This is the hifi forum which may be why many of us have not heard of valve junior. I would imagine more of the guys over in instruments and amps will have heard of it.
I have used led bias, fixed grid bias and battery bias in SRPP and did consider diode bias in cathode followers, but back when I used them I generally directly coupled them to the preceding stage - that did require consideration of filament to cathode insulation issues of course.
These days I use high transconductance triodes and pentodes connected as triodes either driving transformers or loaded by a cascode current source / followers. System is now a rather odd mix of hybrid, all tube, and solid state. I am a big proponent of fixed bias in all forms. There are no auto-bias gain or power stages in any of my current designs.. LOL
I have used led bias, fixed grid bias and battery bias in SRPP and did consider diode bias in cathode followers, but back when I used them I generally directly coupled them to the preceding stage - that did require consideration of filament to cathode insulation issues of course.
These days I use high transconductance triodes and pentodes connected as triodes either driving transformers or loaded by a cascode current source / followers. System is now a rather odd mix of hybrid, all tube, and solid state. I am a big proponent of fixed bias in all forms. There are no auto-bias gain or power stages in any of my current designs.. LOL
Yes. I don't build guitar amps any more, many for those reasons. I did build surface amplifier, mostly for my own personal use. I am thinking of starting another project, using 2 EL-34 per channel, single ended, for 18 watts per channel. But before I do, there are couple more experiments I want to do on my current build, before I start my next project......
I hope you'll share your amplifier project here when the time comes.. Considering triode connection (18W implies probably not) UL or pentode?
I noted long ago that the triode curves of the EL34 looked pretty good, and while I have built many DHT based SE amps over the years I am still waiting to get to that SE EL34 amp.
I noted long ago that the triode curves of the EL34 looked pretty good, and while I have built many DHT based SE amps over the years I am still waiting to get to that SE EL34 amp.
Yes, sir. I certainly will.
Don't know about UL mode. If I did, it would be on a variable control, not a toggle switch. More like driving the screen tap with the second power tube, running in triode mode... and adding some type of another gain stage to drive those power tubes really hard..... and would still move forward with para-feed drive, given it sounds just so lovely.......
is still based on Surface amp approach, meaning the amp is driven from headphone jack of laptop, or tablet computer, or iPhone, and no volume control...(too redundant) I'd call it a Rock-o-la, but that name already taken.......
-g
Don't know about UL mode. If I did, it would be on a variable control, not a toggle switch. More like driving the screen tap with the second power tube, running in triode mode... and adding some type of another gain stage to drive those power tubes really hard..... and would still move forward with para-feed drive, given it sounds just so lovely.......
is still based on Surface amp approach, meaning the amp is driven from headphone jack of laptop, or tablet computer, or iPhone, and no volume control...(too redundant) I'd call it a Rock-o-la, but that name already taken.......
-g
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I must admit, I have better things to do than to research every obscure student project at every obscure university...
Good lord are you still flogging that dead horse? LED bias bas been around for as long as LEDs have been around. And no one else is trying to 'take credit for it', they're just using it like any other well-known electronics tool.
No, I don't think you understand my question.
Let's say Case 1 I need cathode bias of 4V. I drop 3V across the LED and 1V across the resistor from LED to ground.
Case 2 I pump additional external current through the LED and resistor for better LED performance. My bias still needs to be 4V total with 3V on the LED and 1V on the resistor. The resistor will be smaller, but the dc voltage across it will be still 1V. That 1V now pumps more dc current into the secondary, as the resistor to the secondary is much smaller.
Let's say Case 1 I need cathode bias of 4V. I drop 3V across the LED and 1V across the resistor from LED to ground.
Case 2 I pump additional external current through the LED and resistor for better LED performance. My bias still needs to be 4V total with 3V on the LED and 1V on the resistor. The resistor will be smaller, but the dc voltage across it will be still 1V. That 1V now pumps more dc current into the secondary, as the resistor to the secondary is much smaller.
Say you have 1 volt at that junction, regardless of how much current is going through the LED/resistor combination- across a 1K feedback resistor to the secondary, this will be current limited by the feedback resistor, and develop negligible voltage across the secondary. The feedback resistor and the speaker form a voltage divider, so assuming a 1k feedback R and an 8R speaker you'll have .008 volts across the secondary. Quite insignificant.
Cathode resistor in the tube circuit does provide a little local immediately (not loop) corrective feedback, albeit at a loss in gain. The LED does not allow much in the way of this kind of feedback since it fixes the cathode voltage. If you need all the gain you can get, then the diode is the way to go.