Battery Eliminator, Aerodyne's design.

[Mark R]

So as not to hijack tiv48's thread here;
http://golbornevintageradio.co.uk/forum/...php?tid=94&highlight=battery+eliminator

I have started a new one.

Began construction on this eliminator today on some board.


[attachment=614][attachment=615][attachment=616]

The LT side is soldered in, The HT side is for double checking of the connections tomorrow. Then soldering in.

Make up a mains lead and give it a go.

I shall keep you all posted on the progress.

cheers Mark

[Mark R]

Tony

a question for you on this eliminator if I may.

On the HT side with no load I am getting in the region of 110V at the leads, is this expected?
Or will the load of a set drag it down to 90v?

cheers Mark

[Yorkie]

I assume that the HT isn't stabilised, so the off-load voltage will be higher than when on load. I think the easiest way to check this would be by clipping a resistor of an approprate value across the output while observing the voltage. For example, from Ohms law, assuming a nominal HT current of say 27mA (0.027A) at 90 Volts: 90/0.027 = 3,300 Ohms, so a resistor of 3k3 at 90 Volts will pass 27mA. As to Wattage, 90V x 0.027 A = 2.43, so a 2.5 Watt 3k3 resistor should do the trick.

Hope that helps.

David

[Mark R]

David
I am obliged I shall try that and see.
Just need some fiddling on the LT side.

cheers Mark

[Mark R]

Ok quick update on this, The pcb is now complete and functioning.
The plan is to put it in a cabinet with a volt meter for the LT side so it can be varied for different types of heater voltage.
Also got a couple of connectors for different sets so they can be mounted on top of the case.
That will mean a 3 or 4 position switch, shunted by resistors to give the required voltage.
The HT side is 130v but under the load of a 3k3 resistor drops to 70v or so, the LT also varies with a pot.
So things are progressing.

cheers Mark

[Mark R]

Ok guys, a further update,
the PCB is now in the cabinet, I made a switch supply for the LT side so the actual eliminator gives 1.4, 2 and 7.5 volts.
I had to shunt through resistors, the same for the meter to get the correct voltages and readings.
Just need to wire up the mains to the switch and neon then to the Tx.
Oh and redo the labelling.

cheers Mark

[Aerodyne]

I can't do better than to echo David's suggestion about a dummy load to see the HT drop. I think 27mA is rather a high value and I believe you may find the HT approximating more closely to the requisite 90V under the working conditions of the average all-dry receiver. It would be perfectly possible to regulate the HT but IMO an unnecessary complication and expense.
Interested to see how the final build looks, Mark. Pics when possible, please!
-Tony

[Mark R]

Tony (doffs Cap)
no problem, before plugging into a set I do believe some tests are required.
3k3 dropped the HT to some 70v.

cheers Mark

[Aerodyne]

Mark, you may find the regulator voltage settings to be false unless under load. To prevent any inadvertent damage to those delicate 1.4V filaments, I suggest you use the 'dummy load' idea across the LT output to roughly set the voltage and determine the sense of the the preset adjuster, i.e. which way turns the voltage up and which way down. Then before connecting to a set proper, I'd reset to a level below 1 volt. Switch on and monitor the voltage output whilst setting to as close to 1.4V as possible. That way you minmise the risk of damage. You could consider replacing the variable with a fixed resistor (read the pot's 1.4V set value).
I'm sure you will find the HT level will rise to somewhere close to 90V under normal operating conditions. Anywhere above 80V will be fine. The average all-dry portable shouldn't draw more than 12-20mA HT.
Hope this helps.
-Tony

[Aerodyne]

Having just realised that you've used fixed resistors to set the regulator voltage(s) I feel you should be aware that unless your set the output voltage under a correct load you may find that considerable variation occurs. Your carefully selected resistors may be wrong. Result could be a drop in voltage to the point where a set will not function and this may mislead you. Worse still, there may be a damaging rise in voltage. Follow the suggestion made in the post above by fitting a variable and setting it under the loading of an actual working receiver (but ascertain the pot's direction first). I use a large wirewound pot for this procedure but anything will do, including a mini preset.
Looking good, by the way!
-Tony