There must be an Ekco in here!Author: Steve Harris
The AC97 was an unusual model even in it's own time. The rather stark, modernist design by Jesse Collins, was straight out of "Metropolis", and must have looked at if it had landed from another planet in the largely Edwardian living rooms of the period. It was unlike any other Ekco before or since, with it's "Mystic Eye" tuning indicator glinting Cyclops - like from the top of the tall, robotic cabinet. The chassis was also unusual, having a real attempt at controlling the response of the LF amplifier, in place of the usual top cut and then more top cut approach which was the norm. The chassis is in two decks, the power supply at the bottom and the rest on the top, linked by an umbilical cord of wire. The front end is conventional, with an FC4 mixer/oscillator, VP4B IF amp, TDD4 detector and LF amp.
Never mind the qualityThe coupling arrangements then go a bit wierd with various Ls and Cs giving a variable pass filter that can be switched by a 3-position front control marked Fidelity. (This should be marked Boom, Hiss and Muffled, but they opted for 1, 2, and 3). They were obviously proud of this feature, as it has displaced the wavechange switch, which you actually use, to the side of the case, where it has a knob that gives too much leverage, causing the wafer switch to break. The audio is coupled via some hefty 0.2 uf capacitors and a choke thing, and you can bet a pound to a pinch of sugar that the capacitors will all be duff. To leave them is to invite the destruction of the 2P output triode. The use of the single triode output , now so rated in audio circles, was not exclusive to the rarified ranks of high fidelity, for as we will find, Cossor used the same valve in many of their fairly basic models. The 2P is a directly heated triode, a lower power version of the well known PX4. It uses a 2 volt filament, just to be awkward, so it needs it's own winding on the mains transformer, which was no problem to the manufacturer, but is a right headache now, if all is not well...
Back to basicsThe particular set that I am describing was in very original condition inside, the cabinet having had a very neat repair to the bottom, where a piece had broken out. I do not normally bother with damaged cabinet sets, but this one was such a great looking example that I had to buy it. Also, these cabinets are so flimsy that many of them are damaged, and the value of an undamaged example puts them out of reach of many buyers. The chassis looked untouched, apart from some dodgy looking replacement capacitors in the power supply. These got the chop straight away, and nice new ones were fitted, making sure that the resevoir was connected to the below chassis rail, as this set employs negative smoothing using the field coil. The main chassis was given the full capacitor treatment, as all of those nasty B&I ones will be leaky. Lift the earthy end and check for DC volts if you don't believe me. After a quick inspection, it was time to try it. Loud hum, whistles, curious spluttering noise. Tapping anything on the top deck causes unusual sound like a water buffalo passing wind. 2P found to have part of filament O/C and floating about, shorting all electrodes together intermittently. One replacement available, so now just loud screech. Suspect IF instability. Dodgy screening on VP4B confirmed by shorting metallising to chassis. After replacing VP4B, set works superbly. Check bands. O K. Lively, stations in right places. Put chassis back in cabinet, one more try. Dial lamps flicker, loud crackling, burning smell. Switch off, suggest selection of anatomically difficult and illegal practices that the set might care to do were it human, or possibly animal. Suspect own carelessness along the lines of trapping wires under chassis screws etc., but all looks suspiciously well. Pull the whole lot out all over the bench and try again. Frying noise from mains transformer. Take out rectifier, try again. Still frying tonite. Then I spy with my little eye, something beginning with H. Hole in valveholder, between anode and cathode sockets, all blackened. Ha! All is revealed. Arcing has taken place, carbonising the paxolin into a resistor. Reservoir cap is too hot to touch, confirming my theory.
Genius or what?Decide to replace the valveholder in honour of my prompt diagnosis. Find identical holder in donor chassis, and perform transplant. Replace reservoir cap. Switch on. Oh no - new organ has been rejected! Still sizzling. Disconnect all possible sources of shorting. Windings too hot to touch, smell of cooking like the worst kebab stall you have ever smelt. Transformer definitely kaput. This is Bad News. Remember the 2P, with it's 2 volt filament? It needs a 2 volt winding, isolated as it uses a humdinger, then we need a 4 volt for the other valves, then an insulated 4 volt winding for the rectifier. Not to mention the 300-0-300 HT. Rack brain for possible source of such a rare beast. Bush 1938 console, with PX4! No good, all 4v valves.
Down amongst the dead menFlash of inspiration. Cossor - they used 2Ps in those sets with a similar power unit chassis. Venture into back of dismal graveyard of old wireless sets, like Burke and Hare robbing the tombs. Lift down wartime made Cossor, and unscrew the lid, sorry, back. Almost the same valve line - up. Prise out the vital organs, disturbing large spider. Return safely to daylight ready for another hour on the operating table. The transformer tests OK, and has all the right windings, but not the right shape. Make suitable brackets from frame of dead transformer, and it fits a treat. Even the wires connect neatly to the original tagstrip, so plug in and wait.
I want to go homeHum, followed by clouds of acrid smoke and loud pop. Resevoir cap has exploded. Fit another new cap, then on a whim fit the Cossor rectifier that was in the scrap set. Stand back and switch on, finger on the bench supply trip. Music, sounds and sweet airs that give delight and hurt not. Pull out rectifier, and replace with original (Yes, I know, never do that). Music now playing under water, drowned a thousand fathoms deep. Pull it out again quick, and chuck in bin. Did it fall, or was it pushed? Which came first, shorted valve, arcing holder, shorted transformer, chicken or egg? Can I mix any more metaphors without making an omelette? I dont' care, it works. After refitting the chassis it was left on test all day, and to be fair to the designer it sounds very good. It must have been quite something to it's first owner, who had paid out �. 2s. 6d. for this state of the art device.
Cheap at half the price - in 1936Interestingly, that was way above the price of some of the cheaper sets, such as the Philco 444 at �6s., but still not as expensive as others which we do not rate so highly today. The Philips 795A (monoknob) was �.18s., for which you could have had the AC97 and a Philco battery Peoples Set for the servants. With wages at less than a week for a typical office job, the price must have been a decisive factor in choosing which radio to buy, even on H.P. Over the years prices fell and wages rose, making new radios seem cheaper while of course old sets were deemed too costly to repair, and were scrapped. Ironically, because sets like the AC97 are now quite valuable, all the ones that remain are now well worth repairing, and likely to remain so. People who complain that radios are getting too expensive might like to consider that when they were cheap, many people did not think to save them. Most of us can remember radios that are now worth hundreds being put out for the bin men- I remember people burning pre-war sets for the scrap copper wire in the transformers. We are a lot more interested in preserving our heritage if there is a cash incentive!
| Next >