PSU III transformer information.

[colin.hepburn]

Yes my Main is a constant 241v wasn’t the UK 230v because of EU regulations which should be changed back to UK regulations but probley won’t happen I guess
Just my rant on this

[bob orbell]

Thanks all for the help, my mains here is always above 250 and off peek can reach 252, Colin, UK mains voltage has always been 250, but some time ago, maybe when joining the frogs, itiy's and krouts, it was and is quoted as 230 + 10% - 15%, so 253 max 195.5 min . Bob

[John Caswell]

Hi all,
it would be necessary to reduce the input to the tx 1 to 230v, either resistively (Yuk) or fitting another power tx2 secondary of 20Vac in series with the primary of tx1 and isolating tx2 primaries.

John

[Richard]

Surely the draw for Phono is tiny so we could just drop it after the rect and before the caps at R1?

[bob orbell]

Interesting reading this, as a test, I have connected the PSU to my variac, and connected the phono, turning the variac up until 250 volts DC is steady at phono, then tacking a reading of the transformer primary, 187 volts so something clearly wrong with this transformer. Bob

[bikerhifinut]

hmmm well it could be too many turns wound on the HT secondary Bob.
Whats the heater winding showing? It's nominally 9V I guess but not knowing what the regulation figures are for the transformer, it could show a slightly different Voltage.
Now then, assuming theres no inherent fault with the toroid, and its just a winding ratio issue how about winding a few turns over the top in antiphase? You can apply this to either the secondary or the primary depending on whether it's the pri or sec that's got too many turns. you can work out the turns per volt ratio by winding a couple of turns round the top and measuring the voltage, volts/no of turns and that's how many turns per volt you have. Then wind the correct No of turns on to counteract the over voltage and connect in series with the sec or pri depending on how you want to control it, one way it will boost the volts by the no of turns extra and the other (antiphase) should reduce the output volts. It sounds like a faff on but may sometimes be the only practical way to get the desired result.
I imagine removing a few turns off the pri or sec may not be practical as I don't know how they were wound onto the core in the first place,usually they are simple over winds and usually its the primary wound first with secondaries wound over the top if I remember it right.
I've got a similar puzzle at the moment with a toroid that I was given by a pal but its got a 6.3V Heater winding and I would like to raise it to 9V to use a reg on the heater supply, I reckon its worth a try to wind a few extra turns over to get what I need. I reduced a big toroid this way a year ago but that was relatively easy as it was a home wound job off another mate andjust needed a few turns knocking off one of the 9V windings to get 6,3 for the power valves. The hardest part was removing the mylar tape wrapping to get at the windings and then replacing it afterwards! Of course you don't need to do that with a simple overwind using well insulated wire.

Andy.

[Richard]

Doesn't that just indicate it's a higher voltage TX Bob? Did Tiger tell you the specs for that part number?

[bob orbell]

Andy and Richard, this transformer is one of ten made by Tiger for Peter C at his other then business, Arena, it was for the World Design PSU III and is identical to the present PSU III transformer, albeit, no voltage ratings, it has the same part no as the one's supplied by Matthew but, the batch no's differ and quoting these no's to Tiger revealed who ordered them and what they were for, also Tiger never got payed for them. Andy, the low voltage is just over 10 volts and there is no problem with the heater voltage, even Tiger could not explain the very high secondary voltage, so a new one is on it's way from Matthew, fingers crossed. Bob

[Richard]

Morning Bob, thanks for the explanation and hope the new one is easier to implement. What regulator arrangement are you using?

[bob orbell]

Richard, please don't laugh, I got the design from the web, it comprises of two different transistors a 317 regulator and the divider resistors capacitors and one small voltage Zener, I have no claim to knowing much about this sort of stuff, but it works, I had to ask help from a friend as to the base, emitter and collector pins, the first attempt went bang , apparently, I had the Zener round the wrong way , and now hopefully it may survive with the new transformer, time will tell. Bob