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Old 19th Oct 2019, 4:43 pm   #21
allan
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Default Re: DIY battery eliminator for valve radio

I fell asleep a few times through that video... funny.. but when he spotted the new diode he mentioned the lack of a resistor.
Those pyrotechnics inside the last 3S4 reminds me of commissioning a new computer rack in the early 70s. It was assembled at the Plessey Poole factory and delivered to the Plessey Liverpool factory for commissioning. Someone had wired a set of flash bulbs across the mains input switch before it left and you can imagine what happened when the engineers turned it on.
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Old 19th Oct 2019, 5:10 pm   #22
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Default Re: DIY battery eliminator for valve radio

I am insomanic and i watch these vintage radio repair youtube channels in bed helping me to unwind. His voice is kind of mellow and i too fell asleep this morning watching his videos but sometimes they can be very interesting that keep me awake all night.
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Old 20th Oct 2019, 9:42 am   #23
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Default Re: DIY battery eliminator for valve radio

I meant to come back on the fragility of high power IGBTs. Although they're very like high power valves (tubes.. to our ex-colonial friends), unlike the latter whose anodes glow a nice cherry red with a blue glow, IGBTs just explode. The thing that one can overlook is their quoted, sometimes miraculous, rating is good for 25 deg Centigrade and I've seen heatsinks that weigh in at 20 pounds to keep their temperature down.

I have the 1938 Westinghouse booklet with all the calculations needed to understand their practical use which I'll scan sometime, but it has over 40 pages so won't be done straight away.
Unless someone has already scanned it?
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Old 20th Oct 2019, 1:09 pm   #24
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Default Re: DIY battery eliminator for valve radio

The tesla "coilers" have a fair share of IGBT explosions. In double resonance solid state tesla colis, the IGBTs are used for switching the load which is a series LC resonance tank. The switching is timed at the zero-crossings (ZCS)of the load currents to reduce power loss. Any deviation from this soft switching conditions will result in a firecracker like explosion, e.g. parasitic inductance in the circuit that induces voltage spikes.

http://kaizerpowerelectronics.dk/tes...n-guide/igbts/

Going back to the B+ PSU, the series pass regular with negative feedback(two transistors), I meant to copy your rotary switch zener ring arrangement, but i think the momentarily open circuit may generate high voltage pike, so I will stick with simple output tappings.

Last edited by regenfreak; 20th Oct 2019 at 1:14 pm.
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Old 20th Oct 2019, 1:37 pm   #25
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Default Re: DIY battery eliminator for valve radio

Quote:
I meant to copy your rotary switch zener ring arrangement, but i think the momentarily open circuit may generate high voltage pike, so I will stick with simple output tappings.
Make before break switches are avaliable and would stop that happening, alternatively an RC on the output would hold it up long enough for the switch to move.
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Old 20th Oct 2019, 2:01 pm   #26
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Default Re: DIY battery eliminator for valve radio

Quote:
Make before break switches are avaliable and would stop that happening, alternatively an RC on the output would hold it up long enough for the switch to move.
thanks for the suggestion.
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Old 20th Oct 2019, 4:30 pm   #27
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Default Re: DIY battery eliminator for valve radio

I did use a make before break switch in the final design so the voltage wouldn't pop up to the raw HT level. Quite important.
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Old 20th Oct 2019, 5:11 pm   #28
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Default Re: DIY battery eliminator for valve radio

Cheers. I have found a 230-12v 50VA toroid transformer for the A supply that i forgot about, sweet! Just ordered the chinese LT1083 module, 47 ohms PTC thermistor and other bits.
I am planning to run the homebrew AA5 with DC 6.3V, a bit overkill but will be hum free.
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Old 21st Oct 2019, 2:22 am   #29
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Default Re: DIY battery eliminator for valve radio

Quote:
Originally Posted by regenfreak View Post
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.
I bought an old radio power supply for the really old radios using the A,B and C supplies using the zener diode scheme. It was assembled in a fine aluminum enclosure and also includes a volt meter for the filament supply.
It seems like it was designed from the circuit shown on the tubesandmore website.
I have it for many years and use it to test the battery only sets that I restored.
Dave, USradcoll1.
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Old 21st Oct 2019, 5:11 am   #30
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Default Re: DIY battery eliminator for valve radio

If you look carefully at the battery eliminators which I posted links to in the two articles in post #3, you will notice how the filament supplies have over voltage protection incorporated. I think this is an essential part of a good battery eliminator.

In addition, it is important that if you have a battery eliminator with a range of HT output voltages derived from a regulated supply, that you have to allow for a scenario where a connection say to a 135V output might be disconnected and connected to a lower voltage output say 90V by the user. The charge storage in the actual radio (its own filter capacitors) then attempts to inject energy back into the eliminator regulators, say being transistors or IC's, which can destroy them. This is the purpose of the additional diodes you see in series with the HT outputs on the multi-voltage output eliminator. So there needs to be protection for the outputs being forced higher than their normal values. It is often these sorts of things that get completely neglected in many battery eliminator designs.

In addition it is better for these units to have some fusing after the main reservoir capacitors as the fuse values can be lower than when they have to support the initial turn on current surges charging the eliminator's capacitors. Again, these are some of the subtle details that get ignored in many eliminator designs.
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Old 21st Oct 2019, 9:17 am   #31
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Default Re: DIY battery eliminator for valve radio

Continuing the points raised by Argus25...
My day job is to repair circuit boards for lifts and these generally fall into two categories.. well designed and poorly designed. Of course both work and do their jobs but the former include loads of protection devices which are fitted to deal with almost any theoretical eventuality.. including engineer error (which is very common). So a well designed circuit has those extra diodes to deal with reversed current flow plus a multitude of TVS diodes, either C or CA. C types will prevent damage if a higher than normal DC voltage is connected and CA if the higher voltage can also be reversed. The CA types can deal with AC voltages to prevent connection of too high an AC voltage. These TVS diodes can be rated in Kwatts and cannot always be associated with a (local) fuse other than printed circuit track. A good designer will also consider varistors and thermistors.

On the topic of charged capacitors.. a good circuit will have a bleed resistor and a poor circuit will not. I suppose a good circuit suggests a future repairer might step in (health & safety). A bad circuit designer pays no thought to repairers and I include in this group the designers of most Roberts Radios, not charged capacitors.. but rat's nest construction!
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Old 21st Oct 2019, 1:19 pm   #32
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Default Re: DIY battery eliminator for valve radio

Quote:
Originally Posted by allan View Post

On the topic of charged capacitors.. a good circuit will have a bleed resistor and a poor circuit will not.
The good new is that due to the inferior nature of the electrolytic capacitor, its self leakage is relatively high.

Most electrolytic caps of of less than 1000uF capacity charged to a relatively high voltage on the input side of a switch-mode psu self discharge relatively quickly when the power is off, over 10's of minutes, even with no bleeder resistors present.

So provided the engineer doesn't switch off the power & dive in within seconds they are ok.

All engineers working on any high voltage & higher energy storage equipment should be encouraged to switch the apparatus off. Go and have a cup of tea and a biscuit and come back to it in 15 or 20 minutes. The best occupational health and safety advice available today.
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Old 21st Oct 2019, 3:04 pm   #33
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Default Re: DIY battery eliminator for valve radio

I notice you're in Queensland Argus 25.
We asked our Alexa to play Classic Gold FM the other day, thinking it was a local UK station, but much to our surprise it turned out to be in Queensland.
Anyway it's now a firm favourite. Not so many commercials and lots of unusual 50s tunes.
For locals....what about 252KHz from Ireland? It disappeared the other day and a French and a Danish station popped up in its place. Maybe a PA valve needed changing, but it took a week or so wasn't an easy job. Radio 4 is hanging on a thread. They say if a valve pops that'll be the end of 198KHz.
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Old 21st Oct 2019, 5:02 pm   #34
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Default Re: DIY battery eliminator for valve radio

Thanks gents for the insight.

I am copying the B+ schematic of the Tubesandmore kit because it has a negative feedback regulation and it is simple. With the filament A supply , the cheapo chinese LT1083 4 kit is a no brainer, it is cheaper than buying all heatsink components etc separately and it can handle up to max 7.5A:

https://xtronic.org/circuit/circuit-...lators-lt1083/

It has two In4004 diodes doing excatly what you described during connecting and disconnecting the suppy.

I would use a 125mA fast fuse for the B+ output and 1A anti-surge slow fuse for the HT transformer primary. I could connect a properly rate NTC thermistor in the series with the primary of the transformer to tame the initial capacitor charging in-rush current when it is plugged in but i dont think it is necessary in this case.

Then i can get two cheapo analogue voltage meters as panel display.

with the box, i can either get a cheapo wooden box of varying sizes from the local art shop. In the past, i use transparent air tight plastic storage containers. they are cheap, strong and very easy to drill air vent holes. My isolation transformer was housed in such box with cable ties + cable gland compression junction nuts. They are transparent so any smoking component can be seen from outside.

Last edited by regenfreak; 21st Oct 2019 at 5:16 pm.
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Old 21st Oct 2019, 5:22 pm   #35
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Default Re: DIY battery eliminator for valve radio

on the subject of bleeder resistors, it is almost mandatory in any high voltage caps that i have been working with in tesla coils, e.g. RF filter caps or the primary tank HT caps. The difference between with and without bleeders are the missing fingers when someone touches it accidentally.
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Old 21st Oct 2019, 8:08 pm   #36
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Default Re: DIY battery eliminator for valve radio

I suppose one could use a pair of Darlington for handling the high current of a beefy high power B+ transformer.
With a puny B+ transformer, two transistors would be more than enough.
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Old 21st Oct 2019, 9:11 pm   #37
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Default Re: DIY battery eliminator for valve radio

For those who wants to stick with the LM317T, a simple modification using a TIP147 Darlington can boost its current significantly:

http://www.reuk.co.uk/wordpress/elec...age-regulator/

I am lazy and I will stick with the Chinese LT1083 kit
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Old 22nd Oct 2019, 12:07 am   #38
allan
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Default Re: DIY battery eliminator for valve radio

When you use the LT1083 you need a larger heatsink than the one supplied to keep it from getting too hot when running the full current.
I got two complete kits inc cct boards from China ages ago for less than half the price of the RS LT1083. They're a pound or so dearer now and neither RS or Farnell have them. I used one for the T1154 valve heaters.
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Old 22nd Oct 2019, 12:32 am   #39
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Default Re: DIY battery eliminator for valve radio

thanks for the tip Allan
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