Philips 'Superinductance' model 274A

[ppppenguin]

You'll want an isolating transformer with the variac in that setup otherwise the chassis will be at half mains voltage.

[Murphyv310]

You'll want an isolating transformer with the variac in that setup otherwise the chassis will be at half mains voltage.

I'd like to think that the OP would realise this being an engineer Jeffrey!!!
Good advice of course to those contemplating this that are not aware of the implications of this method, having the variac wired straight into the mains!

[ppppenguin]

Even the best of us have made silly mistakes and as you rightly point out, others will be reading this.

For the low HT current needed by a radio you could just use a half wave rectifier on the variac output and have the chassis conencted to neutral. Not sure what sort of derating factor I'd apply to a variac for using it with a half wave rectifier but at least x5. So a 2A variac will be more than adequate.

[Old Sparky]

Those are good suggestions, which would be helpful in establishing whether there are other faults, and I wish I'd thought of them before partially dismantling the radio quite a while ago, then putting it on one side. As things are, though, I'd have to reconnect everything and refit the old components I've removed before being able to carry out the tests you suggested, Trevor. Somewhere I have another mains transformer with which I could make up a seperate HT supply, but it would be easier to connect a couple of silicon diodes with limiting resistor, to the exsisting mains transformer and check for other faults. I don't possess a variac, Jeffrey, but could rig up a Lamp Limiter. The phrase 'fools rush in' sums up my approach to this one so far, as I simply decided that, because of it's age, waxed paper caps, out of tolerance resistors, and maybe electrolytics would need replacing before even attempting to power the set up. I did check valve filaments, coils and the mains Tx for continuity, checked the internal wiring, which is entirely solid cored tinned Cu. wire, much of it sleeved, and visually inspect the valves, which is how I realised that the wrong rectifier, a VU39(ZA13088) was fitted. BTW, as of 30 minutes ago, I still haven't had a reply from the radio's owner.

[Murphyv310]

Hi.
I'm sure the total current would only be in the order of 60ma at the most on a set of this age.
I made up a little supply box from an old wall wart many moons ago which plugs into the variacs output socket, my set up feeds the variac directly from my 2KW isolating TX so its always safe.
I only use this on AC only sets of course, to have the load of the warmed up valves there before applying the HT is very useful, many restored radio's will work on 50v HT with very much reduced volume, interesting to note on a set untouched that they need a lot more HT to give any result than after replacing leaky caps and low valves!

[Murphyv310]

Those are good suggestions, which would be helpful in establishing whether there are other faults, and I wish I'd thought of them before partially dismantling the radio quite a while ago, then putting it on one side.  As things are, though, I'd have to reconnect everything and refit the old components I've removed before being able to carry out the tests you suggested, Trevor.  Somewhere I have another mains transformer with which I could make up a seperate HT supply, but it would be easier to connect a couple of silicon diodes with limiting resistor, to the exsisting mains transformer and check for other faults.  I don't possess a variac, Jeffrey, but could rig up a Lamp Limiter.  The phrase 'fools rush in' sums up my approach to this one so far, as I simply decided that, because of it's age, waxed paper caps, out of tolerance resistors, and maybe electrolytics would need replacing before even attempting to power the set up.  I did check valve filaments, coils  and the mains Tx for continuity, checked the internal wiring, which is entirely solid cored tinned Cu. wire, much of it sleeved, and visually inspect the valves, which is how I realised that the wrong rectifier,  a VU39(ZA13088) was fitted.  BTW, as of 30 minutes ago, I still haven't had a reply from the radio's owner.

Hi.
As John Wakely would say on another forum "Go on plug it in"

[Old Sparky]

According to Philips service data, Trevor, the total HT current with the original valves is <32mA (Adding the Ia and Ig figures together gives 31,15mA, with HT across C1(Reservoir) of 273v, and 230v across the smoothing cap. C2, and at the anode of L1, the first valve of 223v. At the moment I've no way of knowing how close to those figures the radio in question would operate at, but it shouldn't be a problem rigging up a temporary supply capable of 50mA or more at around 250v Finding the time to do so is another matter altogether!!

[ppppenguin]

Not having ironclad underwear like Mr Wakely, why do you think I like my old Solartron HT PSUs