Wall Warts R Us 8)

[Cressy Snr]

Scratching my head trying to get 4V DC for the 4019A battery operated Post Office valves I have recently acquired, I realised I couldn't be arsed to mess about winding magnet wire around toroidal transformer cores, then rectifying and smoothing.

Enter a pair of old Nokia 4.2V 1A cellphone chargers that had been lying at the bottom of a drawer for years.

Cutting off the plug ends and clip leading the bare wire ends to the appropriate base pins of the valves gave a nice rosy glow and exactly 4VDC to the filaments. Bugger all cost and zero hum! through the speakers. The chargers don't even get warm. Filament current draw for the 4019A is 250mA.

I'm curently (geddit?) up to my armpits in clip leads and different cathode resistors experimenting with these valves so I'll report on the sound quality in a few days time, in my 6AS7 amp thread.

Everyone's house must be full of wall warts off long discarded bits of electrical equipment. I have a couple of 5V 5A ones that could be used on 300B heaters. These things are all of double insulated construction so are ideal for instant floating supplies.

For quick lash-ups they are a Godsend if you have got some with the right output voltages/currents for what you want to do. Yes they probably put out tons of UHF hash but they cost nothing to experiment with.

Steve

[shane]

Good idea. I use a spare laptop power supply for the heaters and the input relay switching in my 6550. Handles all four 6550s and the two ecc82s without raising a sweat, and as you say, hum is non-existant. It puts out 19v at up to 6a, so by putting pairs of 6550s in series and feeding the whole lot through a 12v 100w halogen bulb (glows a gentle red and gives a bit of a soft start) I get 6.4v across each 6550.

[Cressy Snr]

Hi Shane,

I knew somebody else had to be using these ready made supplies. They are too convenient to have been overlooked by the ever-resourceful DIYer

In the purist sense, one could be accused of cheating by using these. On the other hand why reinvent the wheel? Life's too short. It's also good recycling practice to take these wall wart/desktop supplies and re-use them in a different context.

Steve

[Paul Barker]

I have a few builders transformers for work.

I have long considered building another otl amp.

Probably sufficient for ht and a smaller one could heat far more 6as7's (in batches of 10, which effectively means 20 triodes per batch) than you would ever want it to.

Amp could be built small and light with a couple of commando plugs on it, one for ht one for filaments.
I mean I'm not in need of my builders transformers when I'm at home and I'm not in need of my OTL amp when I'm at work.

How green am I?

[Cressy Snr]

Probably sufficient for ht and a smaller one could heat far more 6as7's (in batches of 10, which effectively means 20 triodes per batch) than you would ever want it to.

Yikes !

[shane]

Good idea. I use a spare laptop power supply for the heaters and the input relay switching in my 6550. Handles all four 6550s and the two ecc82s without raising a sweat, and as you say, hum is non-existant. It puts out 19v at up to 6a, so by putting pairs of 6550s in series and feeding the whole lot through a 12v 100w halogen bulb (glows a gentle red and gives a bit of a soft start) I get 6.4v across each 6550.

Or at least I did until it gave up the ghost! My power TX has 2 x 6.3v windings, so I wired these up instead of the SMPS, and now I have loads of hum, and I can't use the input relay switching either. What do I need to rectify and smooth the resulting 12.6v? Current requirement is about 6A.