12v heater?

Quite a few Funsters have some form of heating in their van over the winter in the mistaken belief that this somehow will prevent or combat damp when in fact it's just a waste of energy and cost.
The key to avoiding damp is to have some airflow through the van and by cracking open two vents as far apart as possible is all that is needed. However, this may not be the reason you are making the enquiry so I will go further to say running heating from solar power during the winter months whilst feasible is not worth the effort. You would need a shed load of solar and no doubt a large battery bank if running the heater continuously and further to that I'm not convinced a 12 Volt heater would raise the temperature inside a camper by more than 1-3 degrees anyway. I could be wrong though.

For more 12v Tubular Heaterinformation, please contact us. We will provide professional answers.

Subscribers  do not see these advertisements

Contact us to discuss your requirements of Resistive Heating. Our experienced sales team can help you identify the options that best suit your needs.

I have my heater connected, what do I do now?

This is where it gets dangerous. If you’re not comfortable with high voltage, this is a good time for you to say “well this has been a fun learning exercise, I should probably stop now so I don’t get hurt.” I will reiterate this point multiple times, as it frankly can’t be said enough. The voltages present in tube amps and even in tube pedals CAN KILL YOU and will hurt the whole time you’re dying. I don’t want this to feel like gatekeeping, but I can’t emphasize enough that if you aren’t comfortable taking the necessary safety precautions, you really shouldn’t be working on high-voltage circuits. It doesn’t matter how much experience you have, you should always keep in mind how possible a painful death is when dealing with high voltage.

So how can I keep myself safe while working on high-voltage circuits?

There are a couple precautions I recommend when working on high-voltage circuits:

• The one-hand rule. When working on a live circuit like probing voltages during operation for debugging, etc., I keep one hand behind my back. It’s become a reflex now, when my right hand gets close to the circuit, my left hand goes behind my back. I’ve known some techs that stick one hand in their pocket. Anything you can do to avoid having both hands in the circuit at the same time. If you discharge high voltage into your hand it will absolutely hurt and you may get burns, but it won’t kill you. If you have both hands in and the high voltage gets a chance to jump across your heart, you will absolutely die.
• Treat every circuit as though it is energized until proven otherwise. It doesn’t matter how long it’s been unplugged, you avoid touching ANYTHING inside the circuit until you’ve measured anything and everything that could store high voltage. I recommend using one clip lead and one probe lead on a multimeter to measure things. You can use the clip for negative and clip it to the chassis so you can probe voltages with one hand behind your back. ALWAYS check EVERYWHERE before you touch ANYWHERE.
• Respect the circuit. Working on pedals and amps is fun, but when high voltage is involved it’s time to get serious. You should always be at least a little bit afraid, because being too confident can lead to carelessness.
• If you don’t want to follow these steps, please don’t work on high-voltage circuits. Again I don’t want to be the gatekeeper of tube circuits, I’m not the high-voltage police, but even if I’m not legally responsible I don’t want to be morally responsible for someone getting hurt. If you’re not comfortable enough to be safe, please don’t do it. No great tone is worth dying for.

Okay, I understand the risks and I am going to be completely safe. Where do I start?

We already talked about the heaters for the tube, so your tube is heated up and ready to pass some signal. For the real meat, you’re going to need some high voltage for your tube’s plates. As we discussed earlier with tubes, the plate resistor goes between the high voltage supply and sets the gain of the circuit.

Where does the high voltage come from?

There are generally two options for high voltage, transformer or switched-mode power supply (SMPS). We’ll start with transformers as it’s simpler (though probably more likely to kill you if you’re not careful). In amplifiers you need a lot of current, so a transformer is the best option for voltage conversion. You’ll need a rectifier with your transformer, as unlike the heater, the plate needs DC. If the high-voltage secondaries of your power transformer don’t have a center tap, you’ll need a bridge rectifier, like this:



If your power transformer has a center tap on the high voltage secondaries then you can get away with a full-wave rectifier like this:



You will absolutely need to filter this high voltage DC line with some nice big capacitors, and full amplifiers (and more complicated preamps) will have RC filters for each stage of power to isolate them, but the details of how to go about with that is a bit outside the scope of this, so I’ll post some links at the bottom for further reading on power supply filtering.

In pedals where we already have a DC input, it makes sense from a size, cost, and complexity standpoint to use a switched-mode power supply (SMPS) for high voltage. I won’t get into the mechanics of how a SMPS works, but I’ll post a link at the bottom for those that like to understand things. For all points and purposes you can think of SMPS as a voltage regulator that operates more efficiently than a linear regulator (like L78** etc) which means it loses less power in the form of heat. SMPS come in two varieties, buck (step-down) and boost (step-up). We need to take a 9-12V input and kick out some serious high-voltage, so it will not surprise you that we will be using a boost SMPS.

The supply I (and countless others) use for high voltage in pedals is known famously as the “nixie supply” as it was originally used to provide the high voltage for hobbyist nixie tube projects. This is the configuration I use:



C1 needs to be big but the exact value isn’t critical, I’ve since dropped to 100uF for size. I’ve been told the inductor value isn’t critical either, but 100uH inductors aren’t hard to find, so I’ve always stuck with them. Most drawings recommend a 2A or larger inductor, I use 1.8A as they are easy for me to find in a good size package and reasonably priced.

P1 on this drawing is a 5k trimpot, and this is what sets the high voltage. I recommend setting this right around the middle before supplying power, then when power is supplied measure (with one hand behind your back, never put both hands in the circuit at the same time, per the warnings earlier) the output and adjust the trimpot slowly until it gets to the desired value. You’ll have to figure out the best way to do this for you, personally I put a test point on my boards that is a large enough through-hole that I can stick the multimeter probe into it and it will stay there, which frees up my right hand (my left hand stays behind my back at all times) to use a small screwdriver and turn the trimpot.

What ratings do the SMPS components need to be?

You really aren’t seeing the high voltage until you get past the rectifier, so there’s no point in using massive components for the whole things. All resistors can be 1/4W (or even 1/8W), and C7 and C6 can be 50V capacitors. C1 needs to be sized based on your expected input voltage, I use 16V rated caps but higher is of course great. The rectifier diode needs to be an “ultra-fast rectifier” like UF4007, simple rectifiers like 1N4007 will not work.

C2 just needs to be sized for the high voltage that you are planning to run the circuit at.

How high should I run the voltage?

The SMPS schematic posted above is capable of providing around 500V maximum, and you really shouldn’t run a tube preamp that high, your tubes won’t like it. The 12AX7 datasheet recommends a plate voltage between 100 and 250V, but keep in mind that the plate resistor in your circuit will drop the voltage a bit so the plate won’t see the full voltage of the supply (unless it’s a cathode follower, we’ll cover that in another chapter), and even then tubes are generally forgiving devices, and it’s common to exceed the maximum voltages and get away with it.

I still run most of my preamps around 230-240V on the supply, and I use 250V capacitors. Fortunately for us the SMPS is very stable and the voltage doesn’t swing around, so we don’t need a huge margin above the supply voltage. SMPS have a regulated output, which means the output voltage is independent of the input voltage. If I set my regulator for 235V with a 9V then plug a 15V input into it I will still get 235V from the SMPS.

I think that’s pretty much it for power, let me know if there’s anything I missed covering and I can address it. Until next time, this has been “semi-coherent ramblings of a non-expert that has built a couple things with tubes.”

More reading on power supply filtering in amps:

More reading on SMPS:

My previous post on tube preamp design:

This is where it gets dangerous. If you’re not comfortable with high voltage, this is a good time for you to say “well this has been a fun learning exercise, I should probably stop now so I don’t get hurt.” I will reiterate this point multiple times, as it frankly can’t be said enough. The voltages present in tube amps and even in tube pedals CAN KILL YOU and will hurt the whole time you’re dying. I don’t want this to feel like gatekeeping, but I can’t emphasize enough that if you aren’t comfortable taking the necessary safety precautions, you really shouldn’t be working on high-voltage circuits. It doesn’t matter how much experience you have, you should always keep in mind how possible a painful death is when dealing with high voltage.There are a couple precautions I recommend when working on high-voltage circuits:We already talked about the heaters for the tube, so your tube is heated up and ready to pass some signal. For the real meat, you’re going to need some high voltage for your tube’s plates. As we discussed earlier with tubes, the plate resistor goes between the high voltage supply and sets the gain of the circuit.There are generally two options for high voltage, transformer or switched-mode power supply (SMPS). We’ll start with transformers as it’s simpler (though probably more likely to kill you if you’re not careful). In amplifiers you need a lot of current, so a transformer is the best option for voltage conversion. You’ll need a rectifier with your transformer, as unlike the heater, the plate needs DC. If the high-voltage secondaries of your power transformer don’t have a center tap, you’ll need a bridge rectifier, like this:If your power transformer has a center tap on the high voltage secondaries then you can get away with a full-wave rectifier like this:You will absolutely need to filter this high voltage DC line with some nice big capacitors, and full amplifiers (and more complicated preamps) will have RC filters for each stage of power to isolate them, but the details of how to go about with that is a bit outside the scope of this, so I’ll post some links at the bottom for further reading on power supply filtering.In pedals where we already have a DC input, it makes sense from a size, cost, and complexity standpoint to use a switched-mode power supply (SMPS) for high voltage. I won’t get into the mechanics of how a SMPS works, but I’ll post a link at the bottom for those that like to understand things. For all points and purposes you can think of SMPS as a voltage regulator that operates more efficiently than a linear regulator (like L78** etc) which means it loses less power in the form of heat. SMPS come in two varieties, buck (step-down) and boost (step-up). We need to take a 9-12V input and kick out some serious high-voltage, so it will not surprise you that we will be using a boost SMPS.The supply I (and countless others) use for high voltage in pedals is known famously as the “nixie supply” as it was originally used to provide the high voltage for hobbyist nixie tube projects. This is the configuration I use:C1 needs to be big but the exact value isn’t critical, I’ve since dropped to 100uF for size. I’ve been told the inductor value isn’t critical either, but 100uH inductors aren’t hard to find, so I’ve always stuck with them. Most drawings recommend a 2A or larger inductor, I use 1.8A as they are easy for me to find in a good size package and reasonably priced.P1 on this drawing is a 5k trimpot, and this is what sets the high voltage. I recommend setting this right around the middle before supplying power, then when power is supplied measure (with one hand behind your back, never put both hands in the circuit at the same time, per the warnings earlier) the output and adjust the trimpot slowly until it gets to the desired value. You’ll have to figure out the best way to do this for you, personally I put a test point on my boards that is a large enough through-hole that I can stick the multimeter probe into it and it will stay there, which frees up my right hand (my left hand stays behind my back at all times) to use a small screwdriver and turn the trimpot.You really aren’t seeing the high voltage until you get past the rectifier, so there’s no point in using massive components for the whole things. All resistors can be 1/4W (or even 1/8W), and C7 and C6 can be 50V capacitors. C1 needs to be sized based on your expected input voltage, I use 16V rated caps but higher is of course great. The rectifier diode needs to be an “ultra-fast rectifier” like UF4007, simple rectifiers like 1N4007 will not work.C2 just needs to be sized for the high voltage that you are planning to run the circuit at.The SMPS schematic posted above is capable of providing around 500V maximum, and you really shouldn’t run a tube preamp that high, your tubes won’t like it. The 12AX7 datasheet recommends a plate voltage between 100 and 250V, but keep in mind that the plate resistor in your circuit will drop the voltage a bit so the plate won’t see the full voltage of the supply (unless it’s a cathode follower, we’ll cover that in another chapter), and even then tubes are generally forgiving devices, and it’s common to exceed the maximum voltages and get away with it.I still run most of my preamps around 230-240V on the supply, and I use 250V capacitors. Fortunately for us the SMPS is very stable and the voltage doesn’t swing around, so we don’t need a huge margin above the supply voltage. SMPS have a regulated output, which means the output voltage is independent of the input voltage. If I set my regulator for 235V with a 9V then plug a 15V input into it I will still get 235V from the SMPS.I think that’s pretty much it for power, let me know if there’s anything I missed covering and I can address it. Until next time, this has been “semi-coherent ramblings of a non-expert that has built a couple things with tubes.”More reading on power supply filtering in amps: http://valvewizard.co.uk/smoothing.html More reading on SMPS: https://en.wikipedia.org/wiki/Switched-mode_power_supply#Explanation My previous post on tube preamp design: https://forum.pedalpcb.com/threads/tubes-101-intro-to-tube-preamp-design.10625/

Are you interested in learning more about Self-Regulation Ptc Element Heater? Contact us today to secure an expert consultation!