Decca PC/ML Console radio of 1939 find

[Atlantic 52]

Hello to all,
I have been lucky enough to secure a rare Decca PC/ML console radio for restoration. It's in unmolested condition but rather dirty and a bit scratched. I'll have to give it a thorough clean and touch up. I have yet to remove the chassis for inspection but from what I have seen so far it all looks good inside. I have the sales receipt and brochure for it from 1939 which is icing on the cake!

[cathoderay57]

Nice project. The 1937 Decca Prestomatic PT/AC table model has the same chassis (Trader Sheet 304) valves AC/TH1 (although it looks like yours has a Mullard TH4B frequency changer fitted), AC/VP2, 2D4A, AC5/Pen and UU4. Cheers, Jerry

[Herald1360]

Only a short suoperhet hiding behind those five valves, though......

[Simon Gittins]

The PT/AC works well.

Watch out for the external speaker sockets on the primary!

[Boater Sam]

Originally Posted by cathoderay57

Nice project. The 1937 Decca Prestomatic PT/AC table model has the same chassis (Trader Sheet 304) valves AC/TH1 (although it looks like yours has a Mullard TH4B frequency changer fitted), AC/VP2, 2D4A, AC5/Pen and UU4. Cheers, Jerry

I can check if I have that sheet for sale if you wish.
Sam.

[Atlantic 52]

Thanks Sam. I have the PT/ML Trader sheet 328 and the chassis is now out of the cabinet. The autotuning unit is a right pain as once its off I can see its not going to be easy to trouble shoot the set. I guess I can add lengthening wires at the risk of instability. The interior is amazingly clean & bright, it looks untouched too. I have never worked on a Decca radio of the 1930's and its surprising to me to see the different design and manufacture of its components. The large cardboard cased condenser block is a bit of a pain. Could it re-form I wonder? This set has not been powered for over 50 years. Thanks.

[Atlantic 52]

I forgot to say that the cabinet is dated December 1938. The serial number is 73796.

[cathoderay57]

You could try reforming the cardboard capacitor block but I've never yet had success with one. It will probably only get hot and ooze nasty stuff. I recommend disconnecting it then leaving it in situ for appearance's sake and concealing replacement axial electrolytics behind it. You could open it up and re-stuff it but you never know what chemicals are inside. Oh, and be careful with those orange trimmers on the push-button unit. If you don't absolutely have to adjust them, then don't. They are very prone to breaking or the threads go and they just rotate without altering the capacitance. Cheers, Jerry

[Atlantic 52]

Many thanks for the tips Jerry, I'll take heed and take it out of circuit, thought it would be doubtful. I'll try not to adjust those trimmers!

[HamishBoxer]

I would also advise re stuffing that capacitor too.Not worth the risk of reforming.

[DuncanLeece]

Take heart.....I have just done the exact same task in my Decca '44' radiogram pictured, which uses a very similar chassis but with simpler tuning.

I found there was not much space to hide the new caps, so I set to with some rubber gloves and a heat gun out in the garden, and the insides were out of the cardboard box in seconds. The cardboard cleaned up fine, and the three new caps fitted inside perfectly. It really was very simple, and I have nothing remotely like the ability levels of most of the forum members!

Incidentally, the 'BoI' cap in the photo was a replacement some kind former repairer had wired in and then tied inside the gram cabinet with some fence wire.....and that cap was even worse than the original!

The set works pretty well, but I can't claim this is one of the best sounding radiograms I have. Unusual, though, and a nice looking thing, so well worth doing.

best wishes
Duncan

[dazzlevision]

Originally Posted by DuncanLeece

Incidentally, the 'BoI' cap in the photo was a replacement some kind former repairer had wired in and then tied inside the gram cabinet with some fence wire.....and that cap was even worse than the original!

I think "Bol" is actually British Insulated Cables Ltd (principally, a cable manufacturer), which merged with Callender's Cable & Construction Co Ltd in 1945 and the merged company was known as British Insulated Callender’s Cables Ltd. The company name was changed to BICC Ltd, in 1975.

[Atlantic 52]

Thanks to all who have provided input, much appreciated. I like your Decca 44 Duncan, well done for sorting it. Well, I have had a good go at the set today replacing obviously dud or iffy capacitors but found real trouble, my heart sank. The 10" speaker field coil is O/C AND the output transformer has an O/C primary!! Damn, I now need to get serious and its going to take more time. I have cleaned up the set, button polished the cabinet grain and Tops covered the sides. That plus plenty of elbow grease have made it look good. At least its not an eyesore my wife will want out of the house for now!
Regards,
George

[Atlantic 52]

Hi Duncan,
I see you have a TV62. Do you know anyone that wants one in good nick for £115?
Regards,
George

[cathoderay57]

Hi George, the field coil can sometimes be repaired if you are very, very lucky. The first step is to carefully dismantle the speaker. Not a job for the faint hearted but you might want to give it a go. If you can get the field coil off the centre pole piece and then carefully peel back the insulation you might be able to find a break in the wire. It is also possible to fit a replacement field coil if you can source one. The impedance isn't too critical somewhere between 500 Ohms and 1.6 kOhms. If you cannot find one of the exact impedance you can adjust it wiith series or parallel high wattage resistors. You might also want to contact Ed Dinning on this forum 're output transformer and field coil. He may be able to help. Cheers, Jerry

[DuncanLeece]

Thanks George......but TVs aren't really my thing. My TV62 you spotted in the background is a local set in super condition, I really couldn't say no to.....but I will ask a couple of other enthusiasts I know if they are looking for one.
kind regards
Duncan

[Atlantic 52]

Thanks for the tips Jerry. I'll check out the field coil, I did repair one years ago on my 1938 McMichael 368 radiogram. I was burned out about 30 turns in from the outside so was fairly easy to fix. You never know, I'll have to take a look.

[telstar]

Hi. That looks a nice radio.
I have both versions of the Decca PT/AC, the British valve type covered by Trader service sheet 304, and the one with American octal tubes (which someone gave me the service sheet for which was covered by a Brunswick radiogram).
Cheers
Mike

[Atlantic 52]

Thanks Mike, its interesting to learn that two build types were made. From what I can find out it seems that my PC/ML is a rare set. Yesterday I had a go at the field coil. I made up a coil holder cum winding rig on an old piece of chipboard and used a couple of re-inforcement straps to hold the reels. I cut out two hardboard 'caps' to mount the field coil. I'll post a video later but for now enclose some photos. Turning the reels by hand took hours & hours! I finally got to the break and of course they had to be right near the core! Two greenspot points, multiple turns were corroded, one of which had obviously burnt out with current. Cutting a long process short I re-wound the coil bobbin using my battery electric drill with plenty of speed control and care! By 11:30pm I had it wound. I now have to cover and re-solder the connection wires before re-fitting the hum bucking coil. This is not a job for the feint hearted! Does anyone know the gauge of this wire? I don't have a micrometer. Thanks.

[cathoderay57]

Nice job. I saw a spare field coil on eBay but it was going for £55 so you've saved quite a bit! Cheers, Jerry