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Old 16th Oct 2019, 12:33 am   #1
regenfreak
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Default DIY battery eliminator for valve radio

Hi
I will need a B+ [HT+] supply of about 100-110V for a home built from scratch of an 3 valves strip version of an All American Five AA5. I am not ready to go for the valve rectifier yet in my early learning stage and I am conscious of the safety issues. I have the following components:

1) 150W 240V-240V isolation transformer

2) 240V-250V HT 160mA and 6.3V 4A filament valve transformer.

3) 20H choke 75mA

I have seen this battery eliminator 90V, 67.5V and 45V on ebay using two back to back 230V-9V transformers and an IC voltage regulator for the filament supply:

https://www.ebay.co.uk/itm/90-Volt-B...kAAOSwR0JUTlL4

I think the 6V6.uk battery eliminator uses the two 230V-6V transformers as cheap alternative to an isolation transformer, maybe it uses schematic similar to this:

https://antiqueradio.org/bsupply.htm

It uses different values of R3 to give 90V, 67.5V, 45V etc


I am interested in building my fixed 100V B+ battery eliminator using the most simple and reliable solid state rectifier schematic using fast diodes UF4007 to reduce noises.

The supply must be safe and resistant to any open circuit voltage rise ( happens with a swinging choke)and inrush current. And it should not be loaded down easily.



1. What would the best way forward if i use my 240v-250V valve HT transformer to build a simple and stable B+ of 100V with a current of 20-30mA? Shall i use a simple rectifier schematic with smoothing caps with a output voltage dropping resistor if I know in advance the total B+ current of the valves? Do I need to do trial and error to get the exact voltage dropping resistor value?

2. Anyone knows any schematic for vintage battery eliminator like this or similar? It seems the voltage output can be loaded down easily.

https://www.youtube.com/watch?v=x4lDIG_RNl4

I could have build a rectifier module plugged to an isolator transformer using a variac to have variable B+. The rectifier would have C-L-C choke filter. But I prefer a compact power supply and my 3KW variac is a heavy, bulky beast and I dont want to take it out of storage unless I use it for high power projects.

Last edited by regenfreak; 16th Oct 2019 at 1:03 am.
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Old 16th Oct 2019, 1:24 am   #2
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Default Re: DIY battery eliminator for valve radio

There's a great, well designed battery eliminator on this website, IIRC listed under "Things to build". It's an interesting circuit and by it's design, is totally isolated from the mains. Maybe someone can highlight it!
Dave, USradcoll1.
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Old 16th Oct 2019, 5:56 am   #3
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Default Re: DIY battery eliminator for valve radio

Hi,

I have built two DIY battery eliminators.

One used off the shelf back to back Jaycar transformers, the other I rewound the secondary (easy as split bobbins).

If you scroll to the ends of the two articles you can see the designs/schematics there:

http://worldphaco.com/uploads/THE_GREBE_MU-1.pdf

http://worldphaco.com/uploads/UX-171...amplifier..pdf
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Old 16th Oct 2019, 7:00 am   #4
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Default Re: DIY battery eliminator for valve radio

Quote:
Originally Posted by usradcoll1 View Post
There's a great, well designed battery eliminator on this website, IIRC listed under "Things to build". It's an interesting circuit and by it's design, is totally isolated from the mains. Maybe someone can highlight it!
Its here
https://www.vintage-radio.com/projec...y-set-psu.html

Peter
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Old 16th Oct 2019, 12:40 pm   #5
regenfreak
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Default Re: DIY battery eliminator for valve radio

Thanks gentlemen. The 15V transformer step-up quadrupler schematic looks interesting. I will need a simple, reliable and voltage step-down design that is suitable for freebies like me without restoring to circuit design calculations.

Quote:
have built two DIY battery eliminators.

One used off the shelf back to back Jaycar transformers, the other I rewound the secondary (easy as split bobbins).

If you scroll to the ends of the two articles you can see the designs/schematics there:

http://worldphaco.com/uploads/THE_GREBE_MU-1.pdf

http://worldphaco.com/uploads/UX-171...amplifier..pdf
Wow! The Grebre, what a beauty! These are nothing short of being spectacular in workmanship
Thanks! Your calculations in the two articles are very interesting. I will have a good read.

I have a few UX201A, type1A and type 30 valves. All of them are good even they are nearly 90-100 years old. Once I lashed up a regenerative reciever using two UX201A and one type 30 valve using two audio interstage coulping 1:3 transformers. It worked very well.

The UX201A is highly desirbale for audiophiles and it fetches very high price on ebay. The audio fetishists claim it has a unique sound:

http://vinylsavor.blogspot.com/2013/...1-circuit.html

There is something about the orange glow of the UX201A. It is like watching the ember glow of a fireplace while you are sitting on a rocking chair in a cold winter, you dont get this charm and aura from modern tubes.

Last edited by regenfreak; 16th Oct 2019 at 12:52 pm.
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Old 16th Oct 2019, 2:17 pm   #6
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Default Re: DIY battery eliminator for valve radio

Quote:
Originally Posted by regenfreak View Post

The UX201A is highly desirbale for audiophiles and it fetches very high price on ebay. The audio fetishists claim it has a unique sound
Thank you for the kind remarks.

I find it very disturbing that the audiophiles have developed an interest in the 201A. There is nothing about it that is remotely suited to high fidelity audio.

The ill founded, illogical and I'd dare to suggest delusional mystique, attached to it simply drives up the prices and makes it more difficult for a radio restorer, restoring a 1920's vintage radio, to afford replacement valves.

I felt a similar sense of concern when I came across a website claiming that the EF50 was an audiophile valve. To get around the microphonics for audio use they had wrapped them in latex rubber and put them in a PVC tube with a modified base. It made me worry that an electronics restorer and historian might be trying to repair some wartime radar gear and not be able to get a valve at a reasonable price.

While I might seem to be critical of "audiophiles" oddly I am one myself and sport the usual turntable, LP collection, valve amplifier, guitars and guitar amps etc. However there are some audiophile philosophies that I am not prepared to buy into, and calling a 201A valve an audiophile valve is definitely one of them.

(Though I love the orange glow !)
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Old 16th Oct 2019, 2:32 pm   #7
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Default Re: DIY battery eliminator for valve radio

I fully agree. It is very frustrating because any" pair" of 1920-30 radio tubes that can be pre-amp candidates for audiophiles' subjective fetishism can command a high price on ebay. You dont have to look hard on ebay that they become collection trophies for the audiophiles.

Quote:
I felt a similar sense of concern when I came across a website claiming that the EF50 was an audiophile valve. To get around the microphonics for audio use they had wrapped them in latex rubber and put them in a PVC tube with a modified base. It made me worry that an electronics restorer and historian might be trying to repair some wartime radar gear and not be able to get a valve at a reasonable price.
Wrapping them latex rubber and PVC, it certainly consitutes a SM fetish!
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Old 16th Oct 2019, 5:16 pm   #8
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Default Re: DIY battery eliminator for valve radio

One post deleted, eBay rules.
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Old 17th Oct 2019, 1:07 am   #9
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Default Re: DIY battery eliminator for valve radio

In this two part video, he used very much the same unregulated B+ circuit like the link I mentioned earlier (https://antiqueradio.org/bsupply.htm):

https://www.youtube.com/watch?v=qIm9SibSK-c

As an experienced builder, he ran into all kind of problems even with this simple circuit. I think he abandoned it in the 2nd video. It demonstrated the difficulties of building a reliable B+. At the bottom of article there is an alternative circuit using full wave rectifier and zener diodes in series. It is probably a better design:

https://antiqueradio.org/art/PowerSupplySchematic.jpg

Another restorer used the same design to modify this 1940 Silvertone valve battery eliminator (two parts):

https://www.youtube.com/watch?v=PFNUtrJsCxU

Last edited by regenfreak; 17th Oct 2019 at 1:13 am.
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Old 17th Oct 2019, 9:10 am   #10
allan
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Default Re: DIY battery eliminator for valve radio

I built a power supply for a customer's radio a week or so ago.
You can use junk box parts as nothing is really critical. Rather than using back-to-back transformers, because of the availability of small cheap high value capacitors you can use doublers, triplers etc to push up the HT voltage. The case is the only problem, but that was easy as I have lots of defunct computer power supplies which not only provide a nice metal case, IEC mains socket, connecting wires and even HT smoothing capacitors and diodes etc. Mine needed 2 volts for old battery valves so I used a cheap 317T regulator. I took the precaution of adding HT and LT fuses and a 3 volt zener diode. It worked perfectly with no hum. I didn't need a grid bias supply because this was dealt with in the HT negative circuit in the radio, but because of the almost zero current drain a PP3, some AA cells or something suitable is no hardship. construction details below (scroll down to the end of the page). The HT choke is a wound component from a computer PSU but isn't an essential part. Choice of transformer VA rating should be made using the current drain and voltage requirement of the set. You can use a ballast resistor before the regulator to suit the transformer output to keep 317T dissipation within spec.
http://www.radiomuseum.co.uk/mm368.html
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Old 17th Oct 2019, 11:03 am   #11
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Default Re: DIY battery eliminator for valve radio

I have also built a PSU for 1930's kit sets based on a low voltage split bobbin transformer with rewound secondaries as there are plenty of these transformers around. I wound an HT winding and an LT winding and used an LM317 to regulate for 2V. Grid bias is derived from a tripler off the LT winding.
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Old 17th Oct 2019, 4:36 pm   #12
regenfreak
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Default Re: DIY battery eliminator for valve radio

Thanks gentlemen.
Allan, thanks for sharing your interesting article.Good job! I like how you can recycle slavaged parts form old devices. It is also interesting how you use the LED in series 12k resistor as a bleeder and over voltage protection during power off.

I dont have any scrap components or transformers laying around, so last night I ordered an inexpensive 240v-110V 20VA step-down transformer. I am going to copy this design using two high voltage transistors ( TIP47 and MPSW42) as B+ voltage regulator with zener diodes:

https://www.tubesandmore.com/sites/d...les/k-101a.pdf

I am not worried about "C" battery as I only build 3-4 valves battery and AC superhets now. With "A" battery, i have been using acid-lead Cyclon 5AH 2V battery, it tends to last for ages. At moment i also use 600mAH Li-ion 9V batteries for B+ with high drain superhet AC valves.

Last edited by regenfreak; 17th Oct 2019 at 4:52 pm. Reason: error
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Old 18th Oct 2019, 12:22 am   #13
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Default Re: DIY battery eliminator for valve radio

My knowledge and understanding of solid state electronics is not up to scratch but I have found this page useful to get an overview of the basic concepts and the surface understanding how the two transistor regulator works:

http://www.skillbank.co.uk/psu/vr2.htm
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Old 18th Oct 2019, 9:16 am   #14
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Default Re: DIY battery eliminator for valve radio

I think we've moved on a bit since that type of series pass transistor circuit. The newer FETs or IGBTs don't need any power to drive their regulator input.
http://www.radiomuseum.co.uk/power%20supply.html
The IGBT is much like a triode valve in not requiring any grid power for its gate although old radios of course are designed to draw only a small amount of current to keep their HT battery life respectable so one could say that's not as important as say an HT PSU for a transmitter.
For LT, I'm an advocate of the LT1083 (from China) but for only low currents a 317T is readily available.

I didn't find any cheap 240v to 110v transformers for my recent project so I used a salvaged 3xlow voltage type and a voltage doubler which costs next to nothing. I've also used a pair of cheap 240v (120-0-120) split primary transformers back to back in the past. As you might have guessed I hate spending money.
Over the last 25 years as a repairer I've accumulated about a ton of scrap equipment so my junk box comprises 3 large sheds plus the loft above my workshop!
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Old 18th Oct 2019, 3:13 pm   #15
regenfreak
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Default Re: DIY battery eliminator for valve radio

Thanks Allan for the insight and informative article on your regulated HT PSU using IGBT. It is good to be able to recycle hardwares which is good for the environment, otherwise they would end up in landfills or scrap yards.

I really like how you wired the zener diodes to the rotary switch, it is very neat!

My only expreience with IGBT was in the its application in high current and high frequency switching in the Double Resonance Solid State (DRSS) tesla coils. Not long a go, I built a musical tesla coil kit OneTeslaTS made by a company called OneTesla. The kit uses IGBTs. I had some experience of building half wave rectifier solid state tesla coil kit using Mosfets too...and i had blown up quit a few!

With newbie like me, I would be better off to copy a proven, existing HT PSU design without going through the experimental process (and stress) of dealing with burning and smoking components. The design caclulations for a negative feedback transistor regulator circuit is a bit too involved for me

Heavy filament and HT transformers like the one you used in the 19 Set PSU are rare and expensive nowaday. I know a guy who made hand wound valve transformers in the Uk and bought one from him but it was not cheap.
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Old 18th Oct 2019, 5:48 pm   #16
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Default Re: DIY battery eliminator for valve radio

Quote:
Originally Posted by regenfreak View Post
In this two part video, he used very much the same unregulated B+ circuit like the link I mentioned earlier (https://antiqueradio.org/bsupply.htm):

https://www.youtube.com/watch?v=qIm9SibSK-c

As an experienced builder, he ran into all kind of problems even with this simple circuit. I think he abandoned it in the 2nd video. It demonstrated the difficulties of building a reliable B+. At the bottom of article there is an alternative circuit using full wave rectifier and zener diodes in series. It is probably a better design:

https://antiqueradio.org/art/PowerSupplySchematic.jpg

Another restorer used the same design to modify this 1940 Silvertone valve battery eliminator (two parts):

https://www.youtube.com/watch?v=PFNUtrJsCxU
I've been working with these battery valve radios for a good many years, still a pre-teen. The HT supply was always rather simple, but the LT was always a problem. The high value, low voltage electrolytics just weren't that easily available.
For some of those old junky radios, I just used home-brew HT power supply and "D" cells for the LT, as they were inexpensive.
Dave, USradcoll1, always trying to make-do.
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Old 18th Oct 2019, 6:37 pm   #17
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Default Re: DIY battery eliminator for valve radio

I always like to study the schematics of the All American "farmhouse" battery radios. However I have never been able to lay my hand on an American vintage radio, even the 1940-50s amercian radio "tubes" are abundant in Europe. You called them" old junky radios", I call them treasures in the Uk. I have been homebrewing the american classic farmhouse 4 tubes superhets both miniature and Octal base versions, now working on the homebrew of AC AA5 (without live chassis, rectifier and series filaments) and 12V B+ automotive AA5 from scratch.
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Old 19th Oct 2019, 1:03 am   #18
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Default Re: DIY battery eliminator for valve radio

I referred to the junky radios as being not too desirable to the collector group, but they were desirable to me at the time.
As of this time I have a few farm radios, they I built an AC power supply for.
I have one of those Silvertone Power Shifters that I reworked for a post-war Zenith farm radio, that seems to work rather well. This one is one that uses selenium rectifiers for both HT and LT supplies. The set uses 1.4 volt valves.
It's really amazing that the original 1000 mfd capacitors are so large. Now you can use higher value, low voltage Electrolytics and not need the choke.
Dave, USradcoll1, always trying to do it as well or better!
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Old 19th Oct 2019, 10:37 am   #19
regenfreak
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Default Re: DIY battery eliminator for valve radio

I have just come across this; an appropriate dropping resistor is needed in series to compensate the voltage drop when the old selenium rectifier is replaced by modern diode. In this farm radio with a built-in selenium rectifier, he blew three audio output 3S4 tubes in a row because of the LT over voltage:

https://www.youtube.com/watch?v=FH7ZCtGjHow

Plus the usual silver mica migration disease.
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Old 19th Oct 2019, 4:25 pm   #20
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Default Re: DIY battery eliminator for valve radio

The three way portables, AC-DC-battery type used one power supply for both HT and LT sources. You had to be very carful for over voltage conditions.
Those type had a tricky sort of switching arrangement for the valve filaments, for a series-parallel configuration so it can operate on three volts LT. The battery only sets are a lot simpler.
Dave, USradcoll1.
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