Using Nixie tube DC high voltage power supply for tube based pedal builds?

[Rambozo96]

Hello all I had an idea of building just the tube based preamp circuit of the old Maestro EP-2 Echoplex in a stompbox and wondered if these Nixie tube power supply boards that takes a 12VDC supply and steps it up to a higher voltage was suitable for stompbox use. Here's the unit I was looking at

https://www.ebay.com/itm/SIP-Lockdown-Sale-Genuine-NCH6100HV-High-Voltage-DC-Power-Supply-for-Nixie-Tubes/174190647774?pageci=91b4915c-4726-4283-9311-c6ff4a36f1f6

[Marcos - Munky]

It'll probably work. The thing with smps is they could induce some noise, depending on the switching frequency and the board layout. Since those boards are made for nixie tubes, and nixie tubes don't need to worry on noise, the board may or not be noise free for audio applications. You'll have to test it or find somebody that made the test to check if this exact board is noise free.

I've built a few tube circuits (preamps and small amps) and powered them using this smps, which is noise free:


This is a verified layout, if you want to give it a try:

[peterc]

Hi Marcos

How much current can you draw from that Design?

Thx Peter

[GibsonGM]

Hi Marcos

How much current can you draw from that Design?

Thx Peter

I've done the same exact thing, and right now I'm running 2 12AX7's with it, no problem whatsoever, and know many others doing the same...they have quite a mild draw, just a few mA's per triode...can you post your echoplex preamp schematic?  More for curiosity  

[vigilante397]

+1 to what Marcos said about noise. I bought a nixie SMPS kit on ebay several years ago to try with a tube pedal design, and it was switching in the upper audio frequency, making my pedal considerably noisy. I use the same NE555 based supply that Marcos shared (I use a 2N3904 instead of the BC547 and leave out R4), which is beautifully quiet and if I recall correctly can provide 30mA or so.

I would also be interested to see your Echoplex preamp schematic

[Marcos - Munky]

The current output depends on what mosfet you use, the quality of the capacitors (low esr is better) and the inductor.

On the mosfets, some of them run cooler than the others, and allow more current output. You should pick your mosfet for it's Rds, lower Rds will run cooler. The ones I use are the IRF640 (Rds = 0.18r but the max voltage it handles is 200V, so you have to be careful when setting the voltage), IRF644 (Rds = 0.28r and it handles 250V) and IRF740 (Rds = 0.55r, so it'll be hotter, but it handles up to 400V). Keep in mind those voltages are the max voltage the mosfets handles, not the max voltage you'll get from this smps. I think you can get almost 300V using 9V as the input voltage, but any mosfet will be pretty hot at this point, so a heat sink is required.

I think I got about 10mA, maybe a bit more. It's enough to power 3 or 4 12AX7.

[Enthalpix]

I used this kind of supply afew years ago for a tube project with EF86 tubes.
Main noise source was that the power supply for a few Nixie tubes (6 or so) making it designed for relatively high power. With a lighter load the power supply (flyback topology) was going into pulse skipping mode to save power.
Once matched with a sufficiently high resistive load it was fairly quiet with only a purely capacitive filter.

[Rob Strand]

You might want to bump the current rating for the inductor.  Especially if you want to play around with different currents and voltages.

The Rapid/Murata inductor is only rated at 0.67A.   The inductor is probably saturating and that's why the MOSFET tends to heat up.


This post lines-up with what I calculated,

"555 timer boost converter doesn't meet spec"
https://electronics.stackexchange.com/questions/152432/555-timer-boost-converter-doesnt-meet-spec

"As Spehro points out, a 100 µH inductor at a switching frequency of 30 kHz — nominal on time = 16 µs — with a 9V source is going to reach a peak current of 1.44 A. This is really abusing the hell out of a 9V battery, not to mention the I2R losses in both the inductor and the MOSFET. This is also uncomfortably close to the saturation current of the inductor, which only exacerbates the losses."

[Rambozo96]

+1 to what Marcos said about noise. I bought a nixie SMPS kit on ebay several years ago to try with a tube pedal design, and it was switching in the upper audio frequency, making my pedal considerably noisy. I use the same NE555 based supply that Marcos shared (I use a 2N3904 instead of the BC547 and leave out R4), which is beautifully quiet and if I recall correctly can provide 30mA or so.

I would also be interested to see your Echoplex preamp schematic

I'll post the one I drew up later today. I had the idea of just building 2 of those EP-2 preamp sections in one box seeing that the schematic shows it only uses half of a 12AX7 so my idea would be roughly the same concept as the EHX Double Muff but with tube based gain stages. I need to dredge up my tube book to see the different ways to bump up the gain. I wished I knew how much gain the stock preamp had on tap.

[Marcos - Munky]

According to the seller which I got the inductors, mine are rated for 3A. Don't know how trustable is that info, but I once touched the inductor while in use and it wasn't even warm. Also, one thing to add is there's also a chance on the mosfets being counterfeit. I mean, those days you find a fake 4558, why would be different with a IRF mosfet?

That said, on noise level of that smps. Some circuits (mainly small tube amps) may be a little bit susceptible to be a bit noisy based on the position of the smps board related to the rest of the circuit. But for the preamps I built, they're pretty quiet. Once I tested a rectifier preamp using this smps. Very high gain, it was outside of a metal box, near my pc. And since I needed a 6V high-ish current power supply for the heaters, I powered both the heaters and the smps using the only power supply I have that could handle the current: a PSP charger. And it was very quiet. I usually use cheap switching power supplies from aliexpress to power this smps, also quiet.

[Rob Strand]

According to the seller which I got the inductors, mine are rated for 3A.

For most applications a 3A rating should be heaps.   I was only going by the Rapid Electonics part number on the schematic.  From the Murata data it shows 0.67A (Rapid site text 0.66A).

https://www.rapidonline.com/murata-ps-22r104c-100-h-10-radial-leaded-inductor-88-1630

There's no "correct" inductor *unless* you also specify the desired output current *and* voltage, which roughly translates to an output power.  There's a minimum inductor current rating required to achieve that output power.   If you run at low currents say 1mA and  200V the output power is going to be 1/10th that if you are trying to run 10mA and 200V.  At 10mA the (minimum) inductor rating will need to be higher.

There's a point where the circuit losses take over and there is an absolute minimum inductor rating just for the circuit to supply its own circuit losses, at which point there's nothing left for output!     Measuring the efficiency (Pout/Pin) is a good indicator of when the losses are dominating.   You can see how the efficiency nose dives at low currents on this graph (not for the NE555 circuit),



When you increase the output voltage on a boost converter the losses can quickly increase.   It might look fine at 200V but things starts to cook at 400V even with no load.   The point where that occurs is messy to work out.  By using larger inductors (lower resistance), lower Rdson MOSFET, and lower ESR caps it all helps.

[duck_arse]

member transmogrifox has posted extensively on hows and whys of inductors used in smps. I couldn't find the thread I was thinking of, but there is one somewhere.

[Rob Strand]

One of the limitations using an inductor to boost the voltage by a large factor is the MOSFET needs to switch the high current on the low voltage side but also handle high voltages of the output side.   High voltage MOSFETs have higher Rds_on's so the losses end up being higher than they need be.

Using transformer action like this allows you to use lower voltage MOSFETs with lower Rds_on,


There problem then is it's harder to find standard parts.   In a DIY scenario it might be possible to wind thin windings on top of the existing inductor windings.

member transmogrifox has posted extensively on hows and whys of inductors used in smps. I couldn't find the thread I was thinking of, but there is one somewhere.

This one?  He could have posted more than once about that.
https://www.diystompboxes.com/smfforum/index.php?topic=112122.0

[Rob Strand]

This paper is actually pretty good for doing the losses.  You would need to brush-up on the basics before digging into it.
http://vincent.boitier.free.fr/TER/809PET-boost-converter-efficiency-calculations.pdf

One point about the 555 circuit is the switch off-time is constant not the switching frequency.

[caspercody]

Hello

I have been using the attached power supply to power my pre-amp tube builds with no problems, or noise. I have gotten over 400 vdc, and been able to power (3) 12AX& tubes with no problem.

[Marcos - Munky]

I was gonna try a similar design using a MC34063, providing I can get one. It says the output power is 20W, from 40V to 400V. That makes 50mA @ 400V, so high current. This is the design: http://imajeenyus.com/electronics/20111010_40-400V_supply/

I can give a try on this one, but using a 100mH inductor (that's all I have). Do you know how much current this one outputs? Also, what are the resistors' power rates?

[duck_arse]

member transmogrifox has posted extensively on hows and whys of inductors used in smps. I couldn't find the thread I was thinking of, but there is one somewhere.

This one?  He could have posted more than once about that.
https://www.diystompboxes.com/smfforum/index.php?topic=112122.0

indeed yes, that's the thread. he left nothing out, that's for sure. thanks for finding, Rob.

[Rambozo96]

+1 to what Marcos said about noise. I bought a nixie SMPS kit on ebay several years ago to try with a tube pedal design, and it was switching in the upper audio frequency, making my pedal considerably noisy. I use the same NE555 based supply that Marcos shared (I use a 2N3904 instead of the BC547 and leave out R4), which is beautifully quiet and if I recall correctly can provide 30mA or so.

I would also be interested to see your Echoplex preamp schematic

Here is what I came up with for my preamp/booster. Basically 2 EP2's run in series with a switch to choose between running just one pre circuit or two.

[Marcos - Munky]

Some things I noticed:
1- you're lacking a input cap.
2- I'm not sure if S1 will do anything to the circuit.
3- those 2 220K resistors near output1 can be swapepd for a single 470K resistor (or even a single 220K resistor). The same goes for the 2 ones near output2.
4- you probably can get rid of those 22K resistors. You already have a pot to set resistence.

[caspercody]

Not sure on power output, but it has powered (4) tubes no problem. I use 1/2 watt for all, except the (4) parts after the BYV26E. Then I use 1 wattt, and caps rated at minimum 400 vdc. I have used 150 mh with no problem, just make sure they are rated high amp, at least 2amps.