Are you really worried about potential distortion in a vintage, portable, battery-powered wireless? I'd just suck it and see. I might consider adding a big, fat capacitor to help deal with anticipated excess peak current demand. Realistically, though, how often will you have it "turned up to eleven"? In that situation I'd be more concerned about the speaker as a source of distortion.
I note your point, but it would be a mistake to think these old Hackers simply aren't capable of producing high quality sound. If they're properly PSU'd and re-aligned correctly, they sound *way* better than their modern day equivalents. Young people are amazed when they hear the sound quality of a re-furbed Hacker or Roberts.
Definition
Transistor - a girl that used to be your brother
Brian
:-D Nice one Brian, LOL.
In fact you can go back still further. I was at some vintage steam fair over the weekend and there was some chap there with an old wind-up gramaphone playing 78s. This was a compact model so no huge horn sticking out of it. Even so, the volume level and fidelity were hugely impressive. I grew up with these old things and had totally forgotten how effective they were. We had to almost shout to make ourselves heard over the racket coming from the 'phone. Most impressive what they were able to do with little more than a needle and some acoustic ducting. No electrical power at all so very 'green' if you're into that s**te.
Going unregulated improves that. A given va transformer of less volts gives more amps.
I thought they were mostly black. Seriously they were more green in every way, greenies might want to learn why we no longer do things that way.
Well I shall give it a shot anyway as it's trivial to rig up a test. If you're right I shall heap praise on you, tabs. :)
Two issues. The maximum power is constrained by the iron, not usually the windings. However if they have skimped on the secondary wire, you can parallel them IN PHASE and hope they are matched. If not its worse than not trying at all.
If however you are rectifying to DC, the easiest option is to put them is series but split the current between them by using a single diode at each end of a 'centre tapped' secondary. Each winding then conducts for half a cycle and gets to cool down during the other!
This was often done when copper was cheaper than diodes...like in valve rectifier cases.
The absolute most expensive and worst possible solution
use em centre tapped with two diodes, instead of 8, and they wont be fighting each other
You've simply described normal bog-standard 2-diode fullwave rectification, which is certainly one way of achieving what the OP needs for his particular application. Note that each winding will have to deliver the full current on alternate half-cycles, so maybe they will benefit from getting 'rest periods'!
If the windings are connected in parallel, a 4-diode fullwave bridge rectifier will be required. [A single halfwave rectifier would be pretty nasty.] As each pair of the bridge diodes are in series, there will be an additional voltage drop of around 0.7V. Each winding will deliver half the required current every half-cycle, so maybe they don't need rest periods.
Personally, I doubt if there's much advantage, one method over the other.
Indeed, since no one else has...I thought it worth mentioning
which is certainly one way of achieving what the OP needs
Yes. heating wise it raises the maximum capacity. Obviously in terms of voltage drop that is weird anyway, as it all te current flows at peak voltage
The advantages are mostly cost and implementation. In the days when a dual diode valve was pretty expensive, full wave rectification was unheard of, and a single cathode spit anode valve was not hard to construct.
And copper was cheap.
Once semiconductor bridge rectifiers got to be relatively inexpensive, and copper became as expensive as gold plated unicorn farts, the situation reversed.
And that is why few people today even use a mains transformer as such. Its all SMPS! At high frequencies you need far less turns, hence copper, and far less iron, hence ferrite.
Spot on. The copper heating losses will be greater in the 2 diode version, I think by a nominal factor of 2.
I expect the extra 0.7V diode losses will not be significant in terms of a nominal 24V DC average output. (ie 18V x sqrt(2) - 1.4V)
While I agree with most of your points, ICs that cope with 230/350V input voltages require specialist silicon and so small transformers are still used where simplicity and reliability is required with isolation.
Not in plugpacks anymore and hardly ever in mains powered devices anymore.
Increasingly less. You can but a small SMPS on ebay for less than you can buy a small transformer... Just about every mains plug USB charger is now an SMPS..winding small mains transformers is non trivial, too. A lot of very fine wire.
...i inherited a 19" rack mounted disco preamp that hummed. Because it had an iron laminations transformer. I replaced that with a toroid 'on offer' from ebay and that cost me a tenner. New it would be nearer £30...
It is only later that you describe the application!!
You need 2 * 9vDC, you've got 2 windings, so its two halfwave or fullwave rectifiers, two small smoothing capacitors and two cheap regulators. Two electrically-isolated, regulated DC sources.
Job done. Especially if the two batteries are not in series in the radio.
PA
Yes, but only if the radio needs 18v, not a 9v and a 9v. My solution covers both cases.
Quite. But my solution covers both 18v and 9+9v It really emulates two
9v batteries.PA
some 50s & 60s tran radios do require the CT connection. I've even seen them use a CT speaker
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