Power supply for battery valve radios
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2542
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A few years back I designed a power supply for my battery radio collection.
I did a PCB for it because I intended to make a number of them. Here are its features:
1. Fits into a compact plastic case,
2. 38mm deep, so that it will fit inside most radios in place of the batteries.
3. Everything, including the transformers and connectors, fits on the PCB. A very easy build.
4. Galvanically isolated A and B supplies to allow for back bias.
5. Regulated, switchable 1.5v / 2v and 90v / 135v outputs. No hum!
6. Negative bias voltages.
7. Uses readily available components available from e.g. Altronics - no special transformers or high voltage caps.
8. Mains input uses standard 2 pin power cable. Double insulated, no mains earth - just like batteries!
9. Connectors are direct plug-in for 1.5v radios using the common 1.5v and two 45 volt batteries, the matching connectors are implemented as part of the end panel PCB. Phoenix connectors are used for the alternative 2v valve radios.
This power supply is simple but works very well.
I am thinking of making a few more and so I need to get some more boards made.
I'm happy to make the bare PCBs available at my cost for anyone who's interested. The more boards, the cheaper they are! I also have a quantity of the plastic cases. One of the two original sources of these has dried up.
I'll ask Brad to put up the circuit - feel free to roll your own if you like.
Battery Eliminator Circuit Diagram
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Location: Tamworth, NSW
Member since 6 April 2012
Member #: 1126
Postcount: 470
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Ian
I.d be interested in a few PCBs
Ben
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Location: Darlington, WA
Member since 30 March 2016
Member #: 1897
Postcount: 189
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I would be most interested in the circuit as the current project is to get a 1930's regen set running again but with a mains power interface.
It works well on batteries but tends to eat them unless only used for demonstration purposes but the owner want to use it much more than that.
Tis quite a good performer for a 4 valve set only using triodes.
This set uses 30 & 31 etc series valves so a 2V supply is needed as well as Grid bias & 90V B+.
Been eyeing up a spare 240V trannie with 2x 6.3V & 1x 5v & 225v CT HT windings to utilise but its quite bulky but plenty of spare inside the console cabinet.
This is a Harringtons console made in WA.
Lindsay
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2542
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Circuit should be up soon.
It uses two 7VA PCB mount transformers. One has 2 x 6v secondaries and the other, 2 x 15v.
The A+ supply is from the 6v x 2 wired as a centre tapped full wave rectifier, followed by an LM317 adjustable linear reg. The same transformer also supplies the C- bias rectifier.
The B+ is from the two 15 volt secondaries connected in series. That feeds a voltage doubler / tripler rectifier to derive both the 90 volts and the 135 volts. Because of this arrangement we can use readily-available 63v caps.
The PCBs will probably work out at a few dollars, depending on how many I order from China. I'll only charge the piece price because the same tooling charge has to be paid regardless of whether I order 1 or 1000. The more, the cheaper!
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Location: Sydney, NSW
Member since 28 January 2011
Member #: 823
Postcount: 6822
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The PCBs will probably work out at a few dollars, depending on how many I order from China.
Are you wedded to having them made in China? There's a guy on the northern beaches, used by a mate of mine for production jobs, who is good, fast and reasonably priced.
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Administrator
Location: Naremburn, NSW
Member since 15 November 2005
Member #: 1
Postcount: 7466
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File uploaded.
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A valve a day keeps the transistor away...
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Location: Wangaratta, VIC
Member since 21 February 2009
Member #: 438
Postcount: 5483
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I note: No PSU earth.
That prompts a warning.
The way some of our electrical systems are wired will cause many Solid State regulators to go crazy, if ether negative, or positive are directly connected to any form of earth/ ground: It happens here.
I always make provision (as does another, that makes them commercially) to provide RF ground, mainly for the antenna, via a 0.01mfd X/Y Line (mains rated) cap.
Marc
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2542
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Yes GTC I'd prefer to have them made locally if that's possible
There used to be several PCB makers on the beaches. Last was East Coast AFAIK. Local bare PCB production closed down due to environmental issues? Mostly they send production out to China, actually quicker and cheaper than local. So I started going direct.
Who is your contact?
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2542
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Yes Marc the design addresses the issues you raise.
The split bobbin design of the two transformers, as well as complying with AS81558.2.5 has only 2pF capacitance between primary and secondary circuits. The mains connection has no effect on the RF pickup on any of the 20 or so radios I have used it with.
I'm not sure what you mean by:
"The way some of our electrical systems are wired will cause many Solid State regulators to go crazy, if ether negative, or positive are directly connected to any form of earth/ ground: It happens here. "
The LM338 A+ regulator (the higher power version of LM317) has huge thermal and feedback/stability margins and is unconditionally stable under all conditions, including shorted output, capacitive loads and linking either + or - to grounds. This is a very conservative design.
I have built 20 examples of this power supply, most are in daily use here and in Europe.
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Location: Darlington, WA
Member since 30 March 2016
Member #: 1897
Postcount: 189
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Ian,
Neat circuit with but one question..can the 2V heater supply handle a max of 300mA.?? I see from the data sheet that the LM338K can handle 5A but would need a good heatsink though.
If it can then I will take 4 circuit boards please.
Lindsay
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Location: Sydney, NSW
Member since 28 January 2011
Member #: 823
Postcount: 6822
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Ian:
Contact George at L D ELECTRONICS
P.O. Box 448 Avalon 2107
Phone (02) 9974 1189 Fax (02) 9974 5491
My mate says he's the same price as China, faster turnaround and he speaks the lingo.
On big jobs I'm told he will beat a genuine quote from overseas.
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2542
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Hi Lindsay
I've had one here in daily use for a few years now on an Airzone Radiostar, which draws 600mA on the 2v filament supply.
There is only about 4 volts across the regulator at that current drain which means the LM338 dissipates about 2.4 watts. A TO3 package's good theta sink to air spec means it does this quite happily without a heatsink up to about 65 degrees C ambient as I recall from when I designed it.
Thanks GTC. I think I know George, didn't realise he was still around!
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Location: Darlington, WA
Member since 30 March 2016
Member #: 1897
Postcount: 189
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Ian,
Ok that sounds great...look forward to seeing the boards arrive. Agreed that the lower the PD across the reg the less they dissipate...I had to fit a quite substantial heatsink to a TO3 reg package that ran horribly hot handling 1.6A with about 9V across the device on another project. The high ambient temp also did not help in my situation.
After I told a mate over here in WA about your unit he wanted a couple of boards so I had to increase my original order...hence now looking for 4 boards.
Lindsay
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Location: Canberra, ACT
Member since 23 August 2012
Member #: 1208
Postcount: 587
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I would be interested in 1 board and case, if possible.
Thanks,
Maven
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Location: Latham, ACT
Member since 21 February 2015
Member #: 1705
Postcount: 2196
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Me too please. I would like one.
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