How to obtain two volts from dry cells

[vinrads]

OK I could just use a resistor and two 1.5 volt cells, is there a better way?

Mick.

[PaulDarzi]

Hi Mick,

It may help if you give the current and power requirements?
Depending upon usage there are several likely better alternatives if any current/power is drawn.

Cheers, Paul.

[Cobaltblue]

Hi Mick

I am guessing you want to power 2 V filament valves.

I would be inclined to use the a couple of paralleled 18650 batteries from a cheap power bank and use a LDO linear regulator to reduce it to 2V.

Although it's wasteful if you leave the charging circuit in place they would be easy charge so the waste would not be that bad.

I have an old Cameo ARP Radio that uses a filament bulb as the regulator when its connected to 3V dry cells.

Cheers

Mike T

[paulsherwin]

Alternatively you could use two NiMH cells in series with a silicon diode to drop the voltage a bit. 2V valve filaments take a fair bit of current though.

[broadgage]

There is no simple way to reliably achieve this with a variable load.
If the load is fixed, like a 2 volt valve heater then a simple dropper resistance will serve. Ideally use an adjustable rheostat and a voltmeter in order that the heater voltage may be kept constant as the batteries run down.

Or use a single sealed lead acid cell, rather than dry cells.

[HamishBoxer]

What is wrong with a 2 V rechargeable like RS stock?

[Restoration73]

5Ah type;

https://cpc.farnell.com/hawker-energ...97?ost=bt00497

[G6Tanuki]

Yes a 2V rechargeable SLA cell would be my preferred way-ahead.

[Though in times-past portable military radios like the WS18 and WS38 used a pair of carbon-zinc Leclanche cells in series to give 3V, along with series resistors to drop the voltage to 2V for the ARP12, AR8 and ATP4 valves used]

[vinrads]

UThanks for all the suggestions ,sometimes it's good to be wrong ! I was convinced that the two volt battery I had would not fit ,but by moving some .1uf caps I managed to squash it in ,I have now fitted some slimmer caps ,This Mc Michael radio is one I restored some years ago my first attempt of re covering the case with rexine .I had the dials scanned and printed . Mick.

[David G4EBT]

I think that's a McMichael '387 Bijou' TRF portable Mick, released in May 1938.

Rare, and sought after!

[vinrads]

Hi David you are spot on with the model, just out of interest I measured the heater current which is about 600ma,not a problem as it will only be switched on to show interested parties , I now need to find a piece of rexine to cover the back ,I don't know if others have had this problem ,I am finding the spray glue for fixing carpets seems to be letting go after some years ,also I discovered the small tin of Evostic (expensive stuff) only half empty had gone solid Mick.

[Kentode]

That's a gorgeous radio, Mick, I'm going to have to start looking for one!

Sorry I can't help with the problem but if it was me I'd run it with two 1.5 volt D cell's and drop one volt with a large wire-wound ceramic resistor, preferably rechargeable.

[David G4EBT]

Originally Posted by Kentode

That's a gorgeous radio, Mick, I'm going to have to start looking for one!

You might be looking for quite a while, and if you do ever find one, you'll need a deep pocket!

There's also an AC mains superhet version of the 'Bijou' - the '808'.

You can see and hear one at this link, where you'll notice the rather unusual tuning 'bar':

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

'Bijou' is French for 'small' or 'dainty'. I assume that the '837' TRF battery version is of similar dimensions to the mains version. Maybe by the standards of the day, compared to other 'portable' (as in 'luggable'!) radios it was small(ish) but hardly 'dainty'.

Certainly distinctive, eye-catching and quite rare.

Search back through the BVWS auction results as far as you wish and I doubt you'd find one.

[Roger Ramjet]

Hi Mick,

I have seen small 2 Volt Cyclon batteries on ebay for between £12.00 & £15.00 These are lead acid ones so would be suitable for filament loads. Of course they would need a suitable charger.

Rog

[vinrads]

Hi Rog thanks for that ,I did see them but I need to keep the cost down, like I say it will only be used to demonstrate now and again, as I have three of the ones shown fitted in the radio I will leave it at that .Mick.

[stevehertz]

Out of interest, the very first vintage radio that I got, the one that started me on this road back in '77 was a McMichael 808 mains version with a veneered case. It was 'payment' for a guitar setup that I did for a friend. Some years ago I sort of got 'used to' looking at it and sold it. I wish I hadn't, but still, I suppose many of us have done that, let things go then wished we hadn't!

Nice work Mick!

[Cathovisor]

The Ekco P151 portable was designed to operate from dry cells or an accumulator, with the dry cells considered the prime source: the voltage drop was accomplished with a mere resistor.

[vinrads]

Originally Posted by Cathovisor

The Ekco P151 portable was designed to operate from dry cells or an accumulator, with the dry cells considered the prime source: the voltage drop was accomplished with a mere resistor.

Hi I see it is 2.5 ohm I may see what it needs for the Mc Michael ,thanks . Mick.

[Cathovisor]

Originally Posted by vinrads

Hi I see it is 2.5 ohm I may see what it needs for the Mc Michael ,thanks . Mick.

Going through the datasheets for the four valves used in the 387, their filaments add up to 0.4A so once again, 2.5Ω is in order to drop a volt.