Re: [neonixie-l] VFD Filament Current

[gregebert]

Another thing to consider is when to turn filaments on and off. Having a 
PIR motion sensor to turn-off the segment supply is important, because 
long-term you will see dark regions on the phosphor closest to the filament.

Turning filaments on and off too many times will wear them out from thermal 
cycling. Having series resistance to reduce the peak inrush current will 
help a lot to extend their life. But leaving them on 24/7 might lead to 
wearout as well.

I have the same issue with my NIMO tube clock (I expect to post more 
details and a video in a few weeks). NIMO tubes are basically 
irreplaceable, so burning-out a filament is a death sentence for the tube. 
For now, I have programable timers for 3 states:

cold (filaments off)
warm (filaments on, high voltage off)
on (filaments and HV on) - Tubes are readable

To go from cold-to-warm, the software requires a few seconds of PIR 
activity so that peeking into the room wont trigger it.
Warm-to-on will happen with any PIR activity.

What I dont yet know is how long I should keep the clock in the warm state. 
Too short, and there will be excessive filament cycling. Too long, and it 
leads to wearout. For now, the warm timeout is 100 seconds, and the cold 
timeout is 24 hours. After the novelty of this clock wears off, it will be 
put in standby mode where it's just keeping time and the display is 
disabled.

On Wednesday, September 14, 2022 at 6:35:29 AM UTC-7 Paul Andrews wrote:

> Arghh - I accidentally hit send on that last one. So anyway, if you don't 
> plan to use the grid to turn the tube off, you can wire it to the segment 
> positive voltage and ignore the need for a bias. You still might want to 
> put the series resistor in though. The exact value you use is going to 
> depend on the cold and hot resistance of the filament. Oh, also if it 
> wasn't clear from my second point, the series resistor acts as a voltage 
> divider, so you have to figure out what the total total voltage across that 
> resistor and filament should be.
>
> In my VFD clock I needed two different filament voltages, so I use a buck 
> converter to get the larger of the two and used a series resistor to 
> produce the lower. In retrospect it might have been better to use series 
> resistors for both and have a higher regulated voltage - the resistances 
> are all very small and it would help smooth over any variations in 
> individual tubes and resistors.
>
> So the easiest way to figure out these values is to measure the filament 
> resistance when cold to get an initial value for the series resistor, then 
> start experimenting and measuring.
>
> On Wednesday, September 14, 2022 at 9:25:57 AM UTC-4 Paul Andrews wrote:
>
>> I don't know the specs for these specific tubes, but a resistor in series 
>> with the filament servers a couple of purposes:
>>
>>1. It reduces the inrush current (i.e. when the filaments are cold). 
>>The resistance of the filaments is low when they are cold, so if you put 
>>the steady-state voltage across them in that state, there will be a much 
>>greater current. For this purpose the series resistor value should be 
>> high 
>>enough to drop that current within the specified limits of the filament.
>>2. Putting a resistor between 0V and the filament raises the base 
>>voltage of the filament above 0V. If the tube has a grid, it is typically 
>>specified to be at a negative voltage with respect to the filament so 
>> that 
>>it can be guaranteed to cut off the current when pulled to that voltage. 
>> An 
>>easy way to achieve this negative bias is to raise the filament voltage 
>>above 0V and keep the grid at 0V.
>>3. 
>>
>>
>> On Wednesday, September 14, 2022 at 4:16:12 AM UTC-4 Richard Scales wrote:
>>
>>> I think I already see blunders in my original post - the filament is the 
>>> cathode (I think) at 5V, the segments (individual anodes) at 25V giving a 
>>> 19V difference over the grid which is at 5V.
>>> I am unsure as to the correct value of the series resistor for the 
>>> heaters- 10R has been used by others though I would prefer to know how that 
>>> was calculated and indeed whether there are significant gains to be made by 
>>> moving to an A/C drive for the filaments.
>>> - Richard
>>>
>>> On Wednesday, 14 September 2022 at 09:02:24 UTC+1 Richard Scales wrote:
>>>
 Hello everyone,
 I have just managed to acquire a set of these and would ideally like to 
 drive them the best possible way.
 I had initially though about a 5V for the filament and then 24V for the 
 cathodes and grid.
 The clock would only have segments activated when someone is nearby - 
 the segments will not be left on all of the time.
 Now I read about A/C supply to the filaments and wonder if I should be 
 going that way.
 Would anyone be able to post their findings and/or suggest the right 
 way forward?
 [image: VFDsnip.JPG]

 I just noted that the picture 

Re: [neonixie-l] VFD Filament Current

[Paul Andrews]

Arghh - I accidentally hit send on that last one. So anyway, if you don't 
plan to use the grid to turn the tube off, you can wire it to the segment 
positive voltage and ignore the need for a bias. You still might want to 
put the series resistor in though. The exact value you use is going to 
depend on the cold and hot resistance of the filament. Oh, also if it 
wasn't clear from my second point, the series resistor acts as a voltage 
divider, so you have to figure out what the total total voltage across that 
resistor and filament should be.

In my VFD clock I needed two different filament voltages, so I use a buck 
converter to get the larger of the two and used a series resistor to 
produce the lower. In retrospect it might have been better to use series 
resistors for both and have a higher regulated voltage - the resistances 
are all very small and it would help smooth over any variations in 
individual tubes and resistors.

So the easiest way to figure out these values is to measure the filament 
resistance when cold to get an initial value for the series resistor, then 
start experimenting and measuring.

On Wednesday, September 14, 2022 at 9:25:57 AM UTC-4 Paul Andrews wrote:

> I don't know the specs for these specific tubes, but a resistor in series 
> with the filament servers a couple of purposes:
>
>1. It reduces the inrush current (i.e. when the filaments are cold). 
>The resistance of the filaments is low when they are cold, so if you put 
>the steady-state voltage across them in that state, there will be a much 
>greater current. For this purpose the series resistor value should be high 
>enough to drop that current within the specified limits of the filament.
>2. Putting a resistor between 0V and the filament raises the base 
>voltage of the filament above 0V. If the tube has a grid, it is typically 
>specified to be at a negative voltage with respect to the filament so that 
>it can be guaranteed to cut off the current when pulled to that voltage. 
> An 
>easy way to achieve this negative bias is to raise the filament voltage 
>above 0V and keep the grid at 0V.
>3. 
>
>
> On Wednesday, September 14, 2022 at 4:16:12 AM UTC-4 Richard Scales wrote:
>
>> I think I already see blunders in my original post - the filament is the 
>> cathode (I think) at 5V, the segments (individual anodes) at 25V giving a 
>> 19V difference over the grid which is at 5V.
>> I am unsure as to the correct value of the series resistor for the 
>> heaters- 10R has been used by others though I would prefer to know how that 
>> was calculated and indeed whether there are significant gains to be made by 
>> moving to an A/C drive for the filaments.
>> - Richard
>>
>> On Wednesday, 14 September 2022 at 09:02:24 UTC+1 Richard Scales wrote:
>>
>>> Hello everyone,
>>> I have just managed to acquire a set of these and would ideally like to 
>>> drive them the best possible way.
>>> I had initially though about a 5V for the filament and then 24V for the 
>>> cathodes and grid.
>>> The clock would only have segments activated when someone is nearby - 
>>> the segments will not be left on all of the time.
>>> Now I read about A/C supply to the filaments and wonder if I should be 
>>> going that way.
>>> Would anyone be able to post their findings and/or suggest the right way 
>>> forward?
>>> [image: VFDsnip.JPG]
>>>
>>> I just noted that the picture above shows the connection for the grid 
>>> (pin 9 on H1) connected to 5V and not the 24V as used on the cathodes.
>>> The more I think about it - the less clear this all becomes!
>>> I need to get it right in my head before I go breaking something and 
>>> then I would like to get the best possible result via reasonably straight 
>>> forward means.
>>> Would anyone be able to point me in the right direction and/or share 
>>> proven drive methods?
>>> - Richard
>>>
>>>
>>> On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote:
>>>
 Yes! That's exactly what happens. The current through the center-tap is 
 the sum of the anode (segment) current and the grid current. And the peak 
 current through the filament wires is actually *greater* than just the 
 current to heat the filaments.


 *Tomasz* - As you found out, those VFDs draw a lot of current. I have 
 a future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) 
 and 
 I'm just going to use a high-current filament transformer with the 
 center-tap at GND. Grids will NOT be pure DC; closer to full-wave 
 rectified 
 around 15-16V. Segment anodes will be pure DC around 36-40V with 
 current-regulators and non-multiplexed.

 I actually have an Op-amp summer+ADC+Software to monitor the current 
 thru the center-rap  on my NIMO clock to determine the tube health, though 
 it's orders of magnitude smaller (30uA per tube).

>

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Re: [neonixie-l] VFD Filament Current

[Paul Andrews]

I don't know the specs for these specific tubes, but a resistor in series 
with the filament servers a couple of purposes:

   1. It reduces the inrush current (i.e. when the filaments are cold). The 
   resistance of the filaments is low when they are cold, so if you put the 
   steady-state voltage across them in that state, there will be a much 
   greater current. For this purpose the series resistor value should be high 
   enough to drop that current within the specified limits of the filament.
   2. Putting a resistor between 0V and the filament raises the base 
   voltage of the filament above 0V. If the tube has a grid, it is typically 
   specified to be at a negative voltage with respect to the filament so that 
   it can be guaranteed to cut off the current when pulled to that voltage. An 
   easy way to achieve this negative bias is to raise the filament voltage 
   above 0V and keep the grid at 0V.
   3. 
   

On Wednesday, September 14, 2022 at 4:16:12 AM UTC-4 Richard Scales wrote:

> I think I already see blunders in my original post - the filament is the 
> cathode (I think) at 5V, the segments (individual anodes) at 25V giving a 
> 19V difference over the grid which is at 5V.
> I am unsure as to the correct value of the series resistor for the 
> heaters- 10R has been used by others though I would prefer to know how that 
> was calculated and indeed whether there are significant gains to be made by 
> moving to an A/C drive for the filaments.
> - Richard
>
> On Wednesday, 14 September 2022 at 09:02:24 UTC+1 Richard Scales wrote:
>
>> Hello everyone,
>> I have just managed to acquire a set of these and would ideally like to 
>> drive them the best possible way.
>> I had initially though about a 5V for the filament and then 24V for the 
>> cathodes and grid.
>> The clock would only have segments activated when someone is nearby - the 
>> segments will not be left on all of the time.
>> Now I read about A/C supply to the filaments and wonder if I should be 
>> going that way.
>> Would anyone be able to post their findings and/or suggest the right way 
>> forward?
>> [image: VFDsnip.JPG]
>>
>> I just noted that the picture above shows the connection for the grid 
>> (pin 9 on H1) connected to 5V and not the 24V as used on the cathodes.
>> The more I think about it - the less clear this all becomes!
>> I need to get it right in my head before I go breaking something and then 
>> I would like to get the best possible result via reasonably straight 
>> forward means.
>> Would anyone be able to point me in the right direction and/or share 
>> proven drive methods?
>> - Richard
>>
>>
>> On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote:
>>
>>> Yes! That's exactly what happens. The current through the center-tap is 
>>> the sum of the anode (segment) current and the grid current. And the peak 
>>> current through the filament wires is actually *greater* than just the 
>>> current to heat the filaments.
>>>
>>>
>>> *Tomasz* - As you found out, those VFDs draw a lot of current. I have a 
>>> future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) and 
>>> I'm just going to use a high-current filament transformer with the 
>>> center-tap at GND. Grids will NOT be pure DC; closer to full-wave rectified 
>>> around 15-16V. Segment anodes will be pure DC around 36-40V with 
>>> current-regulators and non-multiplexed.
>>>
>>> I actually have an Op-amp summer+ADC+Software to monitor the current 
>>> thru the center-rap  on my NIMO clock to determine the tube health, though 
>>> it's orders of magnitude smaller (30uA per tube).
>>>


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Re: [neonixie-l] VFD Filament Current

[Paul Andrews]

I spent a long time trying to figure out if an AC filament drive was worth 
it. I tried multiple AC circuits. In the end, they all suffered from the 
same problem - the voltage varied with the load. This was a killer for me, 
as I wanted the circuit to work for multiple VFD types. In the end it just 
wasn't worth trying to develop a regulated AC driver for several reasons.

   1. I was driving single-digit VFDs and I wanted to drive them in 
   parallel so that if one failed, the others stayed lit.
   2. If one failed, the voltage across the filaments of the others had to 
   stay the same (so no circuit whose voltage varied because of the load).
   3. The filament length was relatively short (small tubes), so the 
   voltage gradient was small enough that there was no detectable difference 
   in brightness across the length of the filament.


On Wednesday, September 14, 2022 at 6:26:28 AM UTC-4 David Pye wrote:

> It can indeed.
>
> For single digit tubes the brightness gradient isn't usually noticeable 
> but for the multidigit ones eg the one from the adafruit iceclock, it 
> certainly is.
>
> David
>
> On Wed, 14 Sept 2022, 10:42 Adrian Godwin,  wrote:
>
>> Using DC for the filament means there is more accelerating voltage at one 
>> end than the other and results in a noticeable difference in brightness.
>>
>> I have wondered if it could be solved without a transformer by driving 
>> the filament with a h-bridge. 
>>
>> On Wed, Sep 14, 2022 at 9:02 AM Richard Scales  
>> wrote:
>>
>>> Hello everyone,
>>> I have just managed to acquire a set of these and would ideally like to 
>>> drive them the best possible way.
>>> I had initially though about a 5V for the filament and then 24V for the 
>>> cathodes and grid.
>>> The clock would only have segments activated when someone is nearby - 
>>> the segments will not be left on all of the time.
>>> Now I read about A/C supply to the filaments and wonder if I should be 
>>> going that way.
>>> Would anyone be able to post their findings and/or suggest the right way 
>>> forward?
>>> [image: VFDsnip.JPG]
>>>
>>> I just noted that the picture above shows the connection for the grid 
>>> (pin 9 on H1) connected to 5V and not the 24V as used on the cathodes.
>>> The more I think about it - the less clear this all becomes!
>>> I need to get it right in my head before I go breaking something and 
>>> then I would like to get the best possible result via reasonably straight 
>>> forward means.
>>> Would anyone be able to point me in the right direction and/or share 
>>> proven drive methods?
>>> - Richard
>>>
>>>
>>> On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote:
>>>
 Yes! That's exactly what happens. The current through the center-tap is 
 the sum of the anode (segment) current and the grid current. And the peak 
 current through the filament wires is actually *greater* than just the 
 current to heat the filaments.


 *Tomasz* - As you found out, those VFDs draw a lot of current. I have 
 a future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) 
 and 
 I'm just going to use a high-current filament transformer with the 
 center-tap at GND. Grids will NOT be pure DC; closer to full-wave 
 rectified 
 around 15-16V. Segment anodes will be pure DC around 36-40V with 
 current-regulators and non-multiplexed.

 I actually have an Op-amp summer+ADC+Software to monitor the current 
 thru the center-rap  on my NIMO clock to determine the tube health, though 
 it's orders of magnitude smaller (30uA per tube).

> -- 
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>>>  
>>> 
>>> .
>>>
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>>
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Re: [neonixie-l] VFD Filament Current

[David Pye]

It can indeed.

For single digit tubes the brightness gradient isn't usually noticeable but
for the multidigit ones eg the one from the adafruit iceclock, it certainly
is.

David

On Wed, 14 Sept 2022, 10:42 Adrian Godwin,  wrote:

> Using DC for the filament means there is more accelerating voltage at one
> end than the other and results in a noticeable difference in brightness.
>
> I have wondered if it could be solved without a transformer by driving the
> filament with a h-bridge.
>
> On Wed, Sep 14, 2022 at 9:02 AM Richard Scales 
> wrote:
>
>> Hello everyone,
>> I have just managed to acquire a set of these and would ideally like to
>> drive them the best possible way.
>> I had initially though about a 5V for the filament and then 24V for the
>> cathodes and grid.
>> The clock would only have segments activated when someone is nearby - the
>> segments will not be left on all of the time.
>> Now I read about A/C supply to the filaments and wonder if I should be
>> going that way.
>> Would anyone be able to post their findings and/or suggest the right way
>> forward?
>> [image: VFDsnip.JPG]
>>
>> I just noted that the picture above shows the connection for the grid
>> (pin 9 on H1) connected to 5V and not the 24V as used on the cathodes.
>> The more I think about it - the less clear this all becomes!
>> I need to get it right in my head before I go breaking something and then
>> I would like to get the best possible result via reasonably straight
>> forward means.
>> Would anyone be able to point me in the right direction and/or share
>> proven drive methods?
>> - Richard
>>
>>
>> On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote:
>>
>>> Yes! That's exactly what happens. The current through the center-tap is
>>> the sum of the anode (segment) current and the grid current. And the peak
>>> current through the filament wires is actually *greater* than just the
>>> current to heat the filaments.
>>>
>>>
>>> *Tomasz* - As you found out, those VFDs draw a lot of current. I have a
>>> future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) and
>>> I'm just going to use a high-current filament transformer with the
>>> center-tap at GND. Grids will NOT be pure DC; closer to full-wave rectified
>>> around 15-16V. Segment anodes will be pure DC around 36-40V with
>>> current-regulators and non-multiplexed.
>>>
>>> I actually have an Op-amp summer+ADC+Software to monitor the current
>>> thru the center-rap  on my NIMO clock to determine the tube health, though
>>> it's orders of magnitude smaller (30uA per tube).
>>>
 --
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>> 
>> .
>>
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Re: [neonixie-l] VFD Filament Current

[Adrian Godwin]

Using DC for the filament means there is more accelerating voltage at one
end than the other and results in a noticeable difference in brightness.

I have wondered if it could be solved without a transformer by driving the
filament with a h-bridge.

On Wed, Sep 14, 2022 at 9:02 AM Richard Scales 
wrote:

> Hello everyone,
> I have just managed to acquire a set of these and would ideally like to
> drive them the best possible way.
> I had initially though about a 5V for the filament and then 24V for the
> cathodes and grid.
> The clock would only have segments activated when someone is nearby - the
> segments will not be left on all of the time.
> Now I read about A/C supply to the filaments and wonder if I should be
> going that way.
> Would anyone be able to post their findings and/or suggest the right way
> forward?
> [image: VFDsnip.JPG]
>
> I just noted that the picture above shows the connection for the grid (pin
> 9 on H1) connected to 5V and not the 24V as used on the cathodes.
> The more I think about it - the less clear this all becomes!
> I need to get it right in my head before I go breaking something and then
> I would like to get the best possible result via reasonably straight
> forward means.
> Would anyone be able to point me in the right direction and/or share
> proven drive methods?
> - Richard
>
>
> On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote:
>
>> Yes! That's exactly what happens. The current through the center-tap is
>> the sum of the anode (segment) current and the grid current. And the peak
>> current through the filament wires is actually *greater* than just the
>> current to heat the filaments.
>>
>>
>> *Tomasz* - As you found out, those VFDs draw a lot of current. I have a
>> future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) and
>> I'm just going to use a high-current filament transformer with the
>> center-tap at GND. Grids will NOT be pure DC; closer to full-wave rectified
>> around 15-16V. Segment anodes will be pure DC around 36-40V with
>> current-regulators and non-multiplexed.
>>
>> I actually have an Op-amp summer+ADC+Software to monitor the current thru
>> the center-rap  on my NIMO clock to determine the tube health, though it's
>> orders of magnitude smaller (30uA per tube).
>>
>>> --
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> .
>

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Re: [neonixie-l] VFD Filament Current

[Richard Scales]

I think I already see blunders in my original post - the filament is the 
cathode (I think) at 5V, the segments (individual anodes) at 25V giving a 
19V difference over the grid which is at 5V.
I am unsure as to the correct value of the series resistor for the heaters- 
10R has been used by others though I would prefer to know how that was 
calculated and indeed whether there are significant gains to be made by 
moving to an A/C drive for the filaments.
- Richard

On Wednesday, 14 September 2022 at 09:02:24 UTC+1 Richard Scales wrote:

> Hello everyone,
> I have just managed to acquire a set of these and would ideally like to 
> drive them the best possible way.
> I had initially though about a 5V for the filament and then 24V for the 
> cathodes and grid.
> The clock would only have segments activated when someone is nearby - the 
> segments will not be left on all of the time.
> Now I read about A/C supply to the filaments and wonder if I should be 
> going that way.
> Would anyone be able to post their findings and/or suggest the right way 
> forward?
> [image: VFDsnip.JPG]
>
> I just noted that the picture above shows the connection for the grid (pin 
> 9 on H1) connected to 5V and not the 24V as used on the cathodes.
> The more I think about it - the less clear this all becomes!
> I need to get it right in my head before I go breaking something and then 
> I would like to get the best possible result via reasonably straight 
> forward means.
> Would anyone be able to point me in the right direction and/or share 
> proven drive methods?
> - Richard
>
>
> On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote:
>
>> Yes! That's exactly what happens. The current through the center-tap is 
>> the sum of the anode (segment) current and the grid current. And the peak 
>> current through the filament wires is actually *greater* than just the 
>> current to heat the filaments.
>>
>>
>> *Tomasz* - As you found out, those VFDs draw a lot of current. I have a 
>> future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) and 
>> I'm just going to use a high-current filament transformer with the 
>> center-tap at GND. Grids will NOT be pure DC; closer to full-wave rectified 
>> around 15-16V. Segment anodes will be pure DC around 36-40V with 
>> current-regulators and non-multiplexed.
>>
>> I actually have an Op-amp summer+ADC+Software to monitor the current thru 
>> the center-rap  on my NIMO clock to determine the tube health, though it's 
>> orders of magnitude smaller (30uA per tube).
>>
>>>

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Re: [neonixie-l] VFD Filament Current

[Richard Scales]

Hello everyone,
I have just managed to acquire a set of these and would ideally like to 
drive them the best possible way.
I had initially though about a 5V for the filament and then 24V for the 
cathodes and grid.
The clock would only have segments activated when someone is nearby - the 
segments will not be left on all of the time.
Now I read about A/C supply to the filaments and wonder if I should be 
going that way.
Would anyone be able to post their findings and/or suggest the right way 
forward?
[image: VFDsnip.JPG]

I just noted that the picture above shows the connection for the grid (pin 
9 on H1) connected to 5V and not the 24V as used on the cathodes.
The more I think about it - the less clear this all becomes!
I need to get it right in my head before I go breaking something and then I 
would like to get the best possible result via reasonably straight forward 
means.
Would anyone be able to point me in the right direction and/or share proven 
drive methods?
- Richard


On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote:

> Yes! That's exactly what happens. The current through the center-tap is 
> the sum of the anode (segment) current and the grid current. And the peak 
> current through the filament wires is actually *greater* than just the 
> current to heat the filaments.
>
>
> *Tomasz* - As you found out, those VFDs draw a lot of current. I have a 
> future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) and 
> I'm just going to use a high-current filament transformer with the 
> center-tap at GND. Grids will NOT be pure DC; closer to full-wave rectified 
> around 15-16V. Segment anodes will be pure DC around 36-40V with 
> current-regulators and non-multiplexed.
>
> I actually have an Op-amp summer+ADC+Software to monitor the current thru 
> the center-rap  on my NIMO clock to determine the tube health, though it's 
> orders of magnitude smaller (30uA per tube).
>
>>

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