Invicta AR49

[M0TGX Terry]

I bought this set two or three years ago on ebay, and when I collected it, it was, to say the least, in a bit of a sorry state. I have been unable to find anything about it on any of the usual places, but fortunately there was a circuit diagram and components list pasted inside the cabinet. The back was missing, and there seemed to be a lot of extra wires including a couple of toggle switches added by a previous owner to bypass the (non functioning) internal/external speaker muting switch. Sadly, these had been fitted by drilling a couple of half inch holes through the side of the cabinet! The "mains lead" was a length of the sort of 7-core cable used for wiring up car tow bars, with the conductors doing duty as "live" and "Neutral" being formed by twisting together pairs of the individual wires in the cable. I am not particularly a health and safety freak, but even I wasn't going to plug that lot in.

The set is a huge beast, measuring 21.5 inches high by 12.25 inches deep and 17.25 inches wide. The cabinet varnish had darkened to a toffee apple brown, so I carefully removed it with a stanley knife blade, held vertically and used like a cabinet scraper. It all came off quite easily to reveal an attractive multi-coloured veneered surface. I gave it two or three coats of Danish Oil, applied with an old paint brush, then left for a week before going over the two black quadrants at the top and the bars over the speaker with a permanent board marker pen. The speaker cloth responded to a gentle hand wash in lukewarm fairy liquid solution (other washing up products are available). The photos will, I hope show what an acceptable effect this achieved.

After much studying of the circuit diagram, and much head scratching, I removed the two toggle switches and started on the chassis. I am not a natural "capacitor restuffer" but most of the ones on this set were of a type which lives inside a sort of paxolin type tube, so modern replacements were easily inserted. The original valves were all side contact types, but a couple had been replaced with octal equivalents .I masked off everything that couldn't be easily removed from the chassis, and sprayed it with silver paint, having first removed two thin tin-plate above-chassis screens, which looked home made and had been crudely soldered to the chassis. One was so thin it had an edge like a razor blade, but once the bleeding stopped I was able to continue. I assume someone had fitted these to screen the otherwise unscreened IFT's - I've not seen naked versions of IFT's before, and although I intended to fabricate something more elegant, this has not actually proved necessary. The side contact valves were thoroughly cleaned with a fibreglass brush and lashings of Servisol, and the dial was very carefully washed with a gently applied damp sponge, after checking that it wasn't water soluble. Fortunately, it wasn't! Gently introducing it to the mains via a lamp limiter resulted in nothing untoward, and after some experimental adjustment of the IFT cores, it proved very sensitive, and with a good tone, although there's a bit more mains hum than I'd like.

I have recently bought a MiniMod pantry transmitter, and playing a CD of WW2 music via that gives a suitably period ambience and makes the whole thing really come to life. The volume is definitely more than adequate to fill a decent size room, and it has that period "bassy" tone.

The next job is to make a replacement back. Fortunately, this set has a little brother in the form of the Invicta A49, and my example of that set, although still in the round tuit pile after its previous owner plugged it in and a LOT of the magic smoke escaped, does have its original plywood back, so I shall use that as a pattern.

For the record, the valve lineup is EF8, ECH3, EF9, EBL1 and AZ1. The EF8 and EF9 have been replaced with their octal equivalents.

The attached pictures show what a handsome chap the AR49 is. I can't understand why there's no information about it on the web (unless I'm looking in the wrong place, of course). If anyone has any information, I'd be delighted to hear from you.

Here are some "before" pictures.

[M0TGX Terry]

Oops... the first picture in my previous post is, of course, the finished cabinet, not a "before "picture at all. Sorry, most of the "after" pictures are too big, so I'll have to manually resize them, and that should take some time as I have no idea how to do it! As soon as I figure it out, I'll post some.

[McMurdo]

What a handsome set Terry. I love the luxurious use of contrasting veneers on these prewar sets.

[M0TGX Terry]

Thanks for the kind comments, Kevin.
It sounds (to my ears) as good as it looks.

[M0TGX Terry]

Aha, I think I have figured out how to resize my pictures, so we should now have some more "after" pictures, including one showing the two holes carelessly drilled (they're not even level with each other!) by a previous owner. I have a plan to disguise them by getting a small engraved plaque stating when and by whom it was restored, and fixing it over the holes.
The rather unsightly insulating tape on the mains lead and mains transformer is purely temporary, until I make a back for the set. In the meantime it is added protection, in addition to my much repeated mantra of "Ist verboten gefingerpoken"

[dave walsh]

Yes an excellent rescue Terry. A great advert for Danish Oil. The prominence of the lettering re AMATEUR and TRAWLERS is unusual. Is this reflected in the circuitry in any way I wonder?

Dave W

[M0TGX Terry]

Dave, not sure whether there's anything particular about the circuit, but I will scan the circuit diagram tomorrow and post it here. I don't think it will breach forum rules since as far as I can see, it isn't available 'up top' or indeed anywhere else on the Web. Mods,if I'm wrong, please accept my apologies in advance.
Interestingly, the smaller Invicta A49 uses the same dial and covers the same wavebands, but lacks the rf amplifier stage of its big brother.

[GeoffK]

The valve line up is almost the same as the Philips 650A a rare and very pleasant sounding art deco radio. The difference being the ECH3 in place of an EK2 and the Philips has an EM1 magic eye.

[ukcol]

Hi Terry - you have a private message.

[M0TGX Terry]

Here's a copy of the CCT diagram. Sorry it has to be so small but I'm having trouble getting it to the right size for the forum. If it's unclear, and anyone wants a copy, just ask and I can email it to you.

[Nickthedentist]

What a lovely cabinet, and job in refinishing it. Well done indeed!

[G6Tanuki]

An interesting circuit: it's got a RF amplifier, but only a single-stage of audio amplification (presumably using one of the high-slope pentodes that were popular at one time).

What's the IF?

I can understand how if it uses a relatively low IF (125-150KHz) the RF amp (and rather more the associated two signal-frequency tuned circuits) would be really needed to keep images down at the higher frequency end of the SW range. If it has the more-usual 450-470KHz IF then the RF amp is an extra image-rejecting bonus.

Also intriguing is the use of the triode local-oscillator stage as a first-audio-amp when the 'pickup' connection is in use.

[M0TGX Terry]

The IF is stated as 465 kc/s. I do have the Trader sheet for the A49, which uses ECH2, EF9, EBL1 and AZ1, ie very similar to its big brother but minus the rf stage, which also
uses the triode section of the triode hexode as a pre-amp on the "gram" position.
I sense that we may be moving off topic from a success story into a general discussion and I don't want to incur the wrath of the moderators, so if anyone wants to continue the general discussion, perhaps a new thread is needed.
In the meantime, thanks for everyone's input.

[Neil Purling]

EBL1/EBL31 as o/p. It is a Double-diode-pentode. It is a little pricey & rare, though thankfully not in PX4 territory.
Forum Member G4EBT had an interesting article in the BVWS journal on the EBL31. Those that are available are converted EBL1's. However the adapted valve is taller, which is maybe not relevant in the Invicta. If you had one of the round Ekco's the back of the set won't go on.
There was an ingenious adapter that incorporated a pair of diodes & a B9A socket so you could use an EL84, which is very common indeed.
When you found a proper EBL31 the adapter could be removed & nothing had been changed under the chassis.

[M0TGX Terry]

I remember reading that article in the BVWS journal. Fortunately,as can be seen in the photo of the rear of the AR49, headroom above the output valve isn't an issue. There must be at least a foot to 18 inches of clearance. I personally find anything at all cramped or tightly packed a bit of a pain, as I have a problem with my hands which means I can't reach into small spaces. Thank heavens for large pre-war woodies.

[MurphyNut]

What a lovely looking set and beautifully restored, I must look into this "Danish Oil" I've done a lot of cabinet restorations myself but not heard of this product before.