12 volt tube mixer

[ruffrecords]

Talking recnetly with a prospective customer about his 4 or 6 into 2 tube mixer. he asked if battery power was an option. This got me thinking about another thread here where it was suggested an entire tube mixer could be run off a 12V supply bumped up by a couple of SMPS to provide 48V and 250V. I must admit, at the time I was not too keen on the idea as it seemed a little wasteful to use a SMPS to convert mains to 12V only to convert it back up to 250V for the HT. However, as soon as you say could I use a car battery instead of the first SMPS it begins to make sense.

So the basic idea is 12V in to run the heaters and switch it up to 48V and 250V for phantom and HT respectively. There seem to be a few off the shelf 12V to 48V dc/dc convertors but very few 12V to 250V. There was one mentioned in another thread but it is made by an unknown Chinese mmanufacturer. Despite that it looks reasonably good.

https://www.ebay.co.uk/itm/DC-9-24V-to100-250V-40-70W-high-voltage-converter-boost-step-up-power-supply/153220780925?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

Looking closely at the pics of this and others like it I found many use the same PWM chip, the SG3525. This seems to be fairly easy to use although app notes are hard to come by. I did find a blog with an HT supply app:

http://tahmidmc.blogspot.com/2013/01/using-sg3525-pwm-controller-explanation.html

from which it seems fairly easy to use. Another post by the same guy gives details of how to calculate the turns ratio and select a suitable core  (ETD39):

http://tahmidmc.blogspot.com/2012/12/ferrite-transformer-turns-calculation.html

So I am just wondering about adding a 48V winding (probably with a linear reg because the power required is minimal) and designing  a complete switching tube supply. Thoughts?

Cheers

Ian

 

[pvision]

The only caveat I can think of is that car batteries are amongst the least portable things ever developed by man

The Sony NP-1 battery might be a better fit. They are ubiquitous and I am sure there are lots of portable battery packs available that use them. Have a look at film equipment suppliers

I first came across the NP-1 with the Sony PCM-F1 system in the 1980s. It seems the format has continued to this day and is used in Betacam, etc

Available in LiON, etc

https://www.soundkit.co.uk/categories/389610/np1

Nick Froome

 

[scott2000]

How do the inverters work that you use in your car? They put out AC but can you do anything with that???

 

[JohnRoberts]

Car radios used tubes back in the day, IIRC they used vibrators to chop the DC and step it up with transformer (or flyback coil).

JR

[edit- it not an accident that tube heaters are 12v or 6v  [/edit]

 

[ruffrecords]

How do the inverters work that you use in your car? They put out AC but can you do anything with that???

I have seen several posts about using the SG3525 for this by setting the clock frequency to 100Hz. No idea if it works.

Cheers

ian

 

[ruffrecords]

@Nick Froome

Thanks for the link Nick. Biggest seems to be 98Wh.. Heaters alone on a 4 channel mixer are likely to be over 30W, say 50W all up which gives you two hours on a battery. I guess you could diode OR a pair to double that?

Cheers

Ian

 

[NOON]

Also depends a bit on how sensitive you are to heater voltage. Remember that they range from >14V to <12V depending on state of charge, and internal resistance rises as state of charge drops. ALWAYS have appropriate fusing right at the battery and protect the terminals from contact. They will weld a dropped spanner / screwdriver to the terminals and make things very hot.

Actual car battery is a bad choice, they're not deep cycle, but plenty of good 'solar' options around.  Also dead easy to add a regulator and portable solar panel to keep the system topped up on the go or at least extend the life.

Remember if it's Lead Acid you generally don't want to discharge more than about 50% of capacity to maintain battery life.

A 100Ah Lead Acid deep cycle will weigh around 30kg. Heavy, but if you're already lugging around a tube mixer..... I've built several 'portable' power systems for people who are going camping in a car or similar and helped a guy build a bike trailer PA system. (Day job is in solar power related things) Mount it all on a hand truck / trolley with good wheels and they're actually pretty easy to get around.

I have a spreadsheet at work I wrote for calculating battery, solar, breaker and cable sizes for various loads and usage patterns. Boss legally owns it so can't send you a copy, but happy to run numbers through it for you and send results.

 

[Tubetec]

There are VFD invertors for motors  becoming available now cheaply enough , normally it has a key panel and controls for frequency ,voltage, current etc , I think any frequency of mains voltage upto 1000hz is possible from them , most that I saw were mains powered but I believe 12 volt versions exist too , the beauty of these units also is you can very easily ramp up the volts over time with them ,perfect for soft start for the valves. Im not sure of the sine wave purity or if that becomes an issue with audio ,but I guess any switching type arrangement might be the same ,maybe opperating at a higher ac frequency like 400 hz could make things quieter . you could  follow the VFD with the usual bridge and reservoir cap and dial in any voltage or frequency you like , maybe more complicated than it needs to be for the battery mixer where simple dc-dc is all thats required .

A battery power small location mixer with valves is a great idea something like that for classical recordings would be a very desirable thing to have .

I do see some mains  transformers rated to 400 or more cycles , would higher frequency allow better  screening of magnetic feilds than at 50 or 60 hz and lower noise levels ? even directly rectifying the VFD output ,does higher frequency allow smoothing to be more effective ?

 

[Bo Deadly]

I would think that would work quite well actually. SMPS are what 85% efficient? So if you pull 100mA at 250V thats 25W / 1 / 0.85 means you need more like 30W / 12V = 2.5A from the battery which is 45Ah so it would run for 18 hours.

Of course that just for the 250V. With 100mA is good for maybe 20+ triodes so 20 * 150mA for 12.6V heater = 3A. So now you're down to only 9 hours. After other losses and all is said and done let's say you have conservatively half that. So 4+ hours on one car battery for a mixer with 20 triodes. Sounds good to me.

Make the supply a separate unit that is easy to move around on a hand-truck so that you can hook up either the battery supply or the mains supply.

But you would probably have to roll your own SMPS. Aside from the fact that finding a 12V DC/DC converter that puts out 250V, the 12.6V might be even harder. Can you run heaters at 12.0V?

 

[ruffrecords]

But you would probably have to roll your own SMPS. Aside from the fact that finding a 12V DC/DC converter that puts out 250V, the 12.6V might be even harder. Can you run heaters at 12.0V?

Yes you ca run heaters at 12V, I do it all the time. Nominal heater volts is 12.6 but they will take 10% either side of that in their stride so they can certainly go as low as 11.34 and as high as 13.86 volts.

Finding a 12V DC/DC converter that puts out 250V is the real key because without it none of the other things are possible. I found a few on eBay and I have ordered a 70W 250V device  (should easily give 200mA). I was thinking the SG3525 might be a suitable device to start experimeting with and we could also include a phantom supply winding.

Cheers

Ian

 

[PRR]

120VAC through a doubler, or 240VAC to FWB, gives ~~300V DC.

The question is if the AC output is transformer isolated from the battery, enough so you can reference the heaters at/near B-. I have three of these things and I have the *impression* the live/return AC lines float (and the 3rd pin may be battery minus).

 

[scott2000]

Finding a 12V DC/DC converter that puts out 250V is the real key because without it none of the other things are possible.

Cheers

Ian

I just came across this??? Tiny output ??

 

[merlin]

Couldn't you be clever and run the whole lot off the 48V supply? I'm sure you could make a respectable mixer using ECC88s at 48V.

 

[Martin Griffith]

Jim Williams  did a very nice  AN70 on the Linear LT1533 low noise smps,  I attach his higher power version , it may gives you a few ideas

 

[gyraf]

I have been thinking of trying something like https://www.aliexpress.com/item/High-Voltage-Converter-Step-up-Boost-Module-45-390V-DC-DC-Converter-Step-Up-Boost-Module/32705909982.html - it looks like it could be the ticket for projects that you really want to supply via a 12V smps adapter or a battery..

Alternative, e.g. https://www.aliexpress.com/item/DC12-24V-to-DC200-450V-70W-High-Voltage-Converter-Step-Up-Power-Supply-Boost-Module-Free/32770925774.html

The latest trend in HIFI is nixie- and magic eye indicators, opening a market for modules intended for powering such: https://www.aliexpress.com/item/DC-9-12V-TO-80-380V-DC-boost-MC34063-High-Voltage-DC-Converter-NIXIE-Magic-Eye/32926216972.html

For P48, I have had success just stacking two (isolated) 12V-to-2x15V  converters, then post-regulating with zener/transistor as in ISA110.

/Jakob E.

 

[pvision]

I'd go simple: two batteries, one for DC heaters and the other for an SMPS

Maybe have a soft-start circuit for the heaters that pulls in a relay and runs them direct off the battery once they're up to speed?

Nick Froome

 

[ruffrecords]

Couldn't you be clever and run the whole lot off the 48V supply? I'm sure you could make a respectable mixer using ECC88s at 48V.

That is a very interesting idea Merlin. I have just been investigating reducing the HT voltage so my SRPP stages could work without heater elevation which then allows the heaters to (ultimately) share a common with the 12V input - but reducing the HT to 48V is a big step further. To obtain sufficient output stage swing it would have to be single ended transformer loaded, and to obtain sufficient drive we would probably have to parallel a pair of triodes (a la REDD 47) (or maybe we could use come kind of bridge). 48V would have to have very low ripple since PSRR of single ended transformer stage is rather poor. Certianly worth some simulation time.

Cheers

Ian

 

[scott2000]

saw this Dynamotor supply on some HAM site....

I'd guess the military had some of this stuff.....???

 

[ruffrecords]

I have been thinking of trying something like https://www.aliexpress.com/item/High-Voltage-Converter-Step-up-Boost-Module-45-390V-DC-DC-Converter-Step-Up-Boost-Module/32705909982.html - it looks like it could be the ticket for projects that you really want to supply via a 12V smps adapter or a battery..

Alternative, e.g. https://www.aliexpress.com/item/DC12-24V-to-DC200-450V-70W-High-Voltage-Converter-Step-Up-Power-Supply-Boost-Module-Free/32770925774.html

The latest trend in HIFI is nixie- and magic eye indicators, opening a market for modules intended for powering such: https://www.aliexpress.com/item/DC-9-12V-TO-80-380V-DC-boost-MC34063-High-Voltage-DC-Converter-NIXIE-Magic-Eye/32926216972.html

For P48, I have had success just stacking two (isolated) 12V-to-2x15V  converters, then post-regulating with zener/transistor as in ISA110.

/Jakob E.

Once you go the dc/dc route there are quite a few  ready built options out there compared to the ac mains in HT out scenario.

I am always a little wary of super cheap Chinese gear but they are certainly good enough to use on one off projects and to reverse engineer.  There seems to be several popular PWM chips and I have now managed to find some more comprehensive app notes so I feel a little more comfortable evaluating the one I have ordered. It would be nice to find a reputable manufacturer of a 12V to 250V dc/dc convertor.

Cheers

Ian

 

[pucho812]

there seems to be a lot of dc to dc converter options. Most of them are really inexpensive. Are any of them worth their salt?