Portadyne Princess coil puzzler - any thoughts please?

[Aerodyne]

Hi David
In the light of your info I'd make the top coil medium wave, the bottom (24 ohm) long wave and the larger middle coil (70 ohm) the coupling coil. You many need to play about with phase (get the coils conducting in the same direction by reversing connections) to obtain good results.
70 ohm does seem a very high value for a standard coil, however. I suppose it is OK, with no evident damage?
The other thing is that often, the medium and long windings are ready-connected within the former, evidence for which would be a tag with two wires attached! I add this only for completeness as I'm sure I don't need to teach you to suck eggs.
Tony

[Yorkie]

Thanks Tony, and everyone else for your interest, advice and encouragement.

It's all systems go!

I wired the coil with the 4R winding for MW, and the 24R coil in series for LW, with the 70R winding for coupling. I used the same phase (start and finish of the windings) as with the aerial coil, and bingo, the radio burst into life! It performs much better than I'd expected, with excellent volume on just a few feet of wire for an aerial. It's selective, and lots of stations on MW and two or three on LW. The 'volume control/reaction' works just like a normal volume control and isn't touchy to adjust. Unless you knew, you wouldn't know it's a TRF rather than a superhet.

I've not checked the accuracy of the dial compared to the stations, and as I said earlier, I don't have any alignment info, but I'll see what data for similar TRF sets such as Champions say.

I checked the inductance of the various windings on the repaired coil, albeit I’ve no doubt that the phantom fidler who crawled all over this set before it came my way, will have fiddled with the cores of the coil. For what it's worth, the inductances were: MW 166uH, LW, 2.2015 mH, and the coupling coil 10.25mH. Taking the lazy route, I used a resonant frequency calculator, and judging by the size of the tuning cap, I made an assumption that it was about 365pF. (There doesn't look to be enough vanes on it for it to be 500pf, but more vanes than would suggest much lower than 365pF). Using that assumption, this would put the lower end of the MW at 461 Metres, (0.646mHz), and the lower end of LW at 1,694M (0.177mHz). Given that it's a TRF, no doubt if I loose couple my frequency counter to the coil, I could ascertain the actual frequency and tweak the cores and trimmers to line it up with the dial.

The calculator I used for the resonant frequency, and frequency/wavelength converter were:

Resonant Frequency Calculator:

http://www.deephaven.co.uk/lc.html

Frequency to wavelength converter:

http://www.translatorscafe.com/cafe/unit...avelength/

Flushed with success, it’s motivated me to get on with using my back panel router jig to make a back for the set, and while I’m at it, to make one for the Noble set I bought at the NVCF, which has an identical cabinet. I'll then write an article for Carl Glover's consideration for the BVWS Bulletin on making radio backs with a router, as I said I would.

I don’t suppose that these sets are rare, but they certainly seem to be uncommon. The only other person I know who has one is Howard Craven, who was most helpful to me in e-mailing me pictures of his Portadyne Princess, including the back panel, and a pic of what the knobs look like as mine came with no knobs. Not only that, Howard tipped me off a short while latter that he’d spotted a couple on e-bay, which I won, and found a third at the NVCF.

I’ve attached a pic of the back which Howard e-mailed to me. (Though original, it looks rather ill fitting, so I’ll make mine fit a bit more snugly, and will make a label with the wording of the original).

It's just occured to me with it being the Diamond Jubille weekend, that this little set left the factory just two years after the Queen's Coronation, a year after I left school, and rationing ended.

All in all, a very successful day, which started with a morning rummage around the Rufforth Autojumble at York, with Colin and Mike Phelan from ‘over the wall’.

Hope that's of interest.


Life is good - I'm going to give myself a pat on the back!

[pwdrive]

I am pleased you got it all sorted David, a definate result.

Lawrence.

[Yorkie]

I am pleased you got it all sorted David, a definate result.

Lawrence.

Thanks Lawrence - not anything like as arduous as re-roofing a house though eh!

Now that IS a task which deserves 'high fives' on conclusion!

[pwdrive]

It's raining, I have temporay flashed the chimneys with some flashband and an arm full of silicon tubes and a mastic gun! Seems to be holding out so far, going off topic so will leave that.
With your bridge you could probably work out what that coupling coil resonates at if you can work out it's self capacitance.
Glad it's all fixed anyway.

Lawrence.

[Joe]

Glad you've got it going, David.

Cheers

Joe

[Mark R]

Nice one David!
Good spot from Tony.
cheers Mark

[johnmcgivern]

Hi David, well done mate its nice to read all the comments and help.
Email for several calculators but just one small program.
John,
http://www.electronics2000.co.uk/download.php#assistant

[Yorkie]

Thanks for reading the thread John, and for the link to that handy suite of calculators, which I've downloaded.

[tiv48]

very well done.
sad to say i would have given up or at least waited till another coil turned up
rob t