Elevated Heaters + LED Pilot Light

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FourT6and2
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Elevated Heaters + LED Pilot Light

Post by FourT6and2 »

Amp's LED pilot light is powered by the AC Heater circuit (6.3v). I'd like to elevate the heaters by referencing to a spot on the B+ line. Probably about 460v or so. Will probably raise the heater ground reference to 45VDC or so. Will this pose a problem to the LED pilot light? If all I need to do is change the voltage limiting resistor in series with the LED, cool. But will the LED function?
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Re: Elevated Heaters + LED Pilot Light

Post by xtian »

Your tubes want 6.3v for the heaters. Even if you "elevate" the heater voltage, the heaters still see 6.3v, and so will your LED. No change needed.
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Re: Elevated Heaters + LED Pilot Light

Post by FourT6and2 »

xtian wrote: Wed May 31, 2017 11:17 pm Your tubes want 6.3v for the heaters. Even if you "elevate" the heater voltage, the heaters still see 6.3v, and so will your LED. No change needed.
That's what I was thinking (and hoping) lol. Thanks. I didn't know if LEDs react differently or not.
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Re: Elevated Heaters + LED Pilot Light

Post by pompeiisneaks »

Yeah LED's need a specific voltage range, a lower limit or they won't power on, and a max voltage, but on top of that they need a resistor to limit current. If all of that is already right, and you just elevate the heaters, you get the same net voltage drop. Also, you could just do the elevation post led. I.e. 6.3v PT to LED, to a rectified board that then also introduces the elevated voltage into the 'ground' of that part.

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FourT6and2
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Re: Elevated Heaters + LED Pilot Light

Post by FourT6and2 »

pompeiisneaks wrote: Wed May 31, 2017 11:37 pm Yeah LED's need a specific voltage range, a lower limit or they won't power on, and a max voltage, but on top of that they need a resistor to limit current. If all of that is already right, and you just elevate the heaters, you get the same net voltage drop. Also, you could just do the elevation post led. I.e. 6.3v PT to LED, to a rectified board that then also introduces the elevated voltage into the 'ground' of that part.

~Phil
Well it's the power transformer that's getting the elevated DC reference on its center tap for the heaters. And the LED is just run in parallel off that. If the LED will work fine (all else being equal), then I think leaving it alone is the easiest thing to do.

Now I just gotta figure out what limiting resistor to use for the LED I'm going to try. Good thing I found this: http://www.ohmslawcalculator.com/led-re ... calculator
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Re: Elevated Heaters + LED Pilot Light

Post by JazzGuitarGimp »

Why do you want to elevate the heaters all the way to 460V? If you're using standard tubes like 12AX7 and pretty much all the usual suspects for output tubes, they have a max heater to cathode voltage of 200V, and sometimes as much as 300V. Exceed that, and you'll set up a condition for arcing inside the tube, which equates to NFG.

Also, most LED's don't like to see reverse voltage, so you would be advised to use a 1N 4148 diode in series with the LED to block the reverse voltage.
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Re: Elevated Heaters + LED Pilot Light

Post by FourT6and2 »

JazzGuitarGimp wrote: Thu Jun 01, 2017 3:10 am Why do you want to elevate the heaters all the way to 460V?
I don't...
If you're using standard tubes like 12AX7 and pretty much all the usual suspects for output tubes, they have a max heater to cathode voltage of 200V, and sometimes as much as 300V. Exceed that, and you'll set up a condition for arcing inside the tube, which equates to NFG.
Yep, I know that. Maybe there's a miscommunication here? The input for the voltage divider (for DC Elevation) is around 460v. But the divider will create an output voltage (above 0v/ground) of about 45v or so. That is what the heaters will see as an elevated ground reference.
Also, most LED's don't like to see reverse voltage, so you would be advised to use a 1N 4148 diode in series with the LED to block the reverse voltage.
Awesome, thanks! Does it matter what type of LED I use? Somewhere else recommended a 1N4007. And do I just put it in series with the voltage-limiting resistor for the LED?

Also, I have a few LEDs that have built-in diodes. I'm not sure if that's the same thing or not. Here's one example: http://www.mouser.com/ds/2/50/UV5TZ-XXX-XX-881074.pdf

It says "includes a protective zener diode" built into the LED. Probably for something else? Says it's for ESD, so maybe it's not the same thing. It's really hard to find purple/violet LEDs!
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Re: Elevated Heaters + LED Pilot Light

Post by Stevem »

Just put this circuit on your first preamp tube, having elevated heaters buys you little on all the otter tubes!
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Re: Elevated Heaters + LED Pilot Light

Post by FourT6and2 »

Stevem wrote: Thu Jun 01, 2017 10:09 am Just put this circuit on your first preamp tube, having elevated heaters buys you little on all the otter tubes!
Very cool, thanks!

The amp, stock, uses this DC scheme on V1 and V2 already. I am weighing my options to use this or elevated heaters. Transformer has an unused 5v tap. I suppose I could try either:

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Re: Elevated Heaters + LED Pilot Light

Post by JazzGuitarGimp »

FourT6and2 wrote: Thu Jun 01, 2017 10:00 am
JazzGuitarGimp wrote: Thu Jun 01, 2017 3:10 am Why do you want to elevate the heaters all the way to 460V?
I don't...
If you're using standard tubes like 12AX7 and pretty much all the usual suspects for output tubes, they have a max heater to cathode voltage of 200V, and sometimes as much as 300V. Exceed that, and you'll set up a condition for arcing inside the tube, which equates to NFG.
Yep, I know that. Maybe there's a miscommunication here? The input for the voltage divider (for DC Elevation) is around 460v. But the divider will create an output voltage (above 0v/ground) of about 45v or so. That is what the heaters will see as an elevated ground reference.
Also, most LED's don't like to see reverse voltage, so you would be advised to use a 1N 4148 diode in series with the LED to block the reverse voltage.
Awesome, thanks! Does it matter what type of LED I use? Somewhere else recommended a 1N4007. And do I just put it in series with the voltage-limiting resistor for the LED?

Also, I have a few LEDs that have built-in diodes. I'm not sure if that's the same thing or not. Here's one example: http://www.mouser.com/ds/2/50/UV5TZ-XXX-XX-881074.pdf

It says "includes a protective zener diode" built into the LED. Probably for something else? Says it's for ESD, so maybe it's not the same thing. It's really hard to find purple/violet LEDs!
Yes, definitely a miscommunication.....on the receiving end :-) After re-reading your original post, I see I missed the part about 45V elevation. My apologies.

As for LED protection, the part you linked needs no further protection; the built-in zener is fine. Also, now that you are considering DC powered heaters, the additional diode won't be necessary if you power the LED from the DC heater supply; it's only needed if you're powering the LED from an AC supply. If you do choose to use a standard (no zener) LED with an AC supply, connect the protection diode (1N4148 or 1N400x) in parallel with the LED, but in reverse: LED anode to 1N4148 cathode and LED cathode to 1N4148 anode. The addition of the protection diode won't affect the LED current limit resistor calculation.
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Re: Elevated Heaters + LED Pilot Light

Post by Stevem »

My first concern is having minimum of semiconductors to rely on and have fail .
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
FourT6and2
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Re: Elevated Heaters + LED Pilot Light

Post by FourT6and2 »

JazzGuitarGimp wrote: Thu Jun 01, 2017 3:37 pm
FourT6and2 wrote: Thu Jun 01, 2017 10:00 am
JazzGuitarGimp wrote: Thu Jun 01, 2017 3:10 am Why do you want to elevate the heaters all the way to 460V?
I don't...
If you're using standard tubes like 12AX7 and pretty much all the usual suspects for output tubes, they have a max heater to cathode voltage of 200V, and sometimes as much as 300V. Exceed that, and you'll set up a condition for arcing inside the tube, which equates to NFG.
Yep, I know that. Maybe there's a miscommunication here? The input for the voltage divider (for DC Elevation) is around 460v. But the divider will create an output voltage (above 0v/ground) of about 45v or so. That is what the heaters will see as an elevated ground reference.
Also, most LED's don't like to see reverse voltage, so you would be advised to use a 1N 4148 diode in series with the LED to block the reverse voltage.
Awesome, thanks! Does it matter what type of LED I use? Somewhere else recommended a 1N4007. And do I just put it in series with the voltage-limiting resistor for the LED?

Also, I have a few LEDs that have built-in diodes. I'm not sure if that's the same thing or not. Here's one example: http://www.mouser.com/ds/2/50/UV5TZ-XXX-XX-881074.pdf

It says "includes a protective zener diode" built into the LED. Probably for something else? Says it's for ESD, so maybe it's not the same thing. It's really hard to find purple/violet LEDs!
Yes, definitely a miscommunication.....on the receiving end :-) After re-reading your original post, I see I missed the part about 45V elevation. My apologies.

As for LED protection, the part you linked needs no further protection; the built-in zener is fine. Also, now that you are considering DC powered heaters, the additional diode won't be necessary if you power the LED from the DC heater supply; it's only needed if you're powering the LED from an AC supply. If you do choose to use a standard (no zener) LED with an AC supply, connect the protection diode (1N4148 or 1N400x) in parallel with the LED, but in reverse: LED anode to 1N4148 cathode and LED cathode to 1N4148 anode. The addition of the protection diode won't affect the LED current limit resistor calculation.
So, while I'm building one of these for myself, I do already have one of these amps already built from Ceriatone. V1 and V2 use DC Heaters (the schematic I posted above). The rest of the heaters are regular AC. And the LED in the amp is powered from the AC Heaters (referenced to ground). And there is no diode. Hasn't been a problem with it in the years I've had it. Is the diode just a safety thing or what?
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Re: Elevated Heaters + LED Pilot Light

Post by JazzGuitarGimp »

FourT6and2 wrote: Thu Jun 01, 2017 5:43 pm
JazzGuitarGimp wrote: Thu Jun 01, 2017 3:37 pm
FourT6and2 wrote: Thu Jun 01, 2017 10:00 am

I don't...



Yep, I know that. Maybe there's a miscommunication here? The input for the voltage divider (for DC Elevation) is around 460v. But the divider will create an output voltage (above 0v/ground) of about 45v or so. That is what the heaters will see as an elevated ground reference.



Awesome, thanks! Does it matter what type of LED I use? Somewhere else recommended a 1N4007. And do I just put it in series with the voltage-limiting resistor for the LED?

Also, I have a few LEDs that have built-in diodes. I'm not sure if that's the same thing or not. Here's one example: http://www.mouser.com/ds/2/50/UV5TZ-XXX-XX-881074.pdf

It says "includes a protective zener diode" built into the LED. Probably for something else? Says it's for ESD, so maybe it's not the same thing. It's really hard to find purple/violet LEDs!
Yes, definitely a miscommunication.....on the receiving end :-) After re-reading your original post, I see I missed the part about 45V elevation. My apologies.

As for LED protection, the part you linked needs no further protection; the built-in zener is fine. Also, now that you are considering DC powered heaters, the additional diode won't be necessary if you power the LED from the DC heater supply; it's only needed if you're powering the LED from an AC supply. If you do choose to use a standard (no zener) LED with an AC supply, connect the protection diode (1N4148 or 1N400x) in parallel with the LED, but in reverse: LED anode to 1N4148 cathode and LED cathode to 1N4148 anode. The addition of the protection diode won't affect the LED current limit resistor calculation.
So, while I'm building one of these for myself, I do already have one of these amps already built from Ceriatone. V1 and V2 use DC Heaters (the schematic I posted above). The rest of the heaters are regular AC. And the LED in the amp is powered from the AC Heaters (referenced to ground). And there is no diode. Hasn't been a problem with it in the years I've had it. Is the diode just a safety thing or what?
It really depends on the LED. Some LED's are sensitive to reverse voltage, some not. Have a look at the attached datasheet and you will see an absolute maximum reverse voltage of 5V. When connected to an AC supply, the reverse voltage seen by the LED will be the peak AC voltage. So in a 6.3V circuit, you will have a peak reverse voltage of 6.3x1.414=8.9V, which is well outside the absolute maximum rating. Not knowing whether the LED might be replaced by someone down the road, it's good engineering practice to add the protection diode.

http://www.mouser.com/ds/2/90/cree.C503 ... 310350.pdf
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FourT6and2
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Re: Elevated Heaters + LED Pilot Light

Post by FourT6and2 »

JazzGuitarGimp wrote: Thu Jun 01, 2017 6:06 pm
FourT6and2 wrote: Thu Jun 01, 2017 5:43 pm
JazzGuitarGimp wrote: Thu Jun 01, 2017 3:37 pm

Yes, definitely a miscommunication.....on the receiving end :-) After re-reading your original post, I see I missed the part about 45V elevation. My apologies.

As for LED protection, the part you linked needs no further protection; the built-in zener is fine. Also, now that you are considering DC powered heaters, the additional diode won't be necessary if you power the LED from the DC heater supply; it's only needed if you're powering the LED from an AC supply. If you do choose to use a standard (no zener) LED with an AC supply, connect the protection diode (1N4148 or 1N400x) in parallel with the LED, but in reverse: LED anode to 1N4148 cathode and LED cathode to 1N4148 anode. The addition of the protection diode won't affect the LED current limit resistor calculation.
So, while I'm building one of these for myself, I do already have one of these amps already built from Ceriatone. V1 and V2 use DC Heaters (the schematic I posted above). The rest of the heaters are regular AC. And the LED in the amp is powered from the AC Heaters (referenced to ground). And there is no diode. Hasn't been a problem with it in the years I've had it. Is the diode just a safety thing or what?
It really depends on the LED. Some LED's are sensitive to reverse voltage, some not. Have a look at the attached datasheet and you will see an absolute maximum reverse voltage of 5V. When connected to an AC supply, the reverse voltage seen by the LED will be the peak AC voltage. So in a 6.3V circuit, you will have a peak reverse voltage of 6.3x1.414=8.9V, which is well outside the absolute maximum rating. Not knowing whether the LED might be replaced by someone down the road, it's good engineering practice to add the protection diode.

http://www.mouser.com/ds/2/90/cree.C503 ... 310350.pdf
Thanks for all the help :)
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