This "Recent Repair" was kindly contributed by Tim Pullin.
Three waveband superhet in a spherical metal enclosure
Valve line-up 6K8G, 6K7G, 6SQ7G, 6V6G, Rect 5Z4
This radio was featured, with its owner Jack Konynenburg, on the BBC Television programme "Antiques Roadshow" on 9th November 2003. I have recorded the excerpt as an AVI video clip. It can be played using Microsoft Media Player 6.4 and later. To reduce download size, the AVI file is packed in a ZIP file.
Click here to download (file size 7MB)
This video clip is copyright © 2003 British Broadcasting Corporation.
It's not an ashtray, or a prop from "Space 1999", it's a radio. Honest! Preceding Sputnik by a decade this unique and classic set was designed by a Polish refugee just after WW2 and built by the Emor radio company in North London.
The Emor Globe was available in some pastel colours, and gold or chrome finish. The latter seems to be the most popular. There was also a "stumpy" table model. The speaker is in the top of the sphere, wrapped in cloth to protect it from dust, and mounted on two struts secured to the circular chassis, all anchored to the sturdy base by a hollow column. The equatorial band is the tuning dial, a light is fixed to the stationary chassis and the whole globe turns about it, the light indicating the selected station. The volume and wave-change switches are knurled sections on the column, operating tubes up it's centre. The mains cable and aerial also feed up this centre tube. An ingenious and unique design.
But how does it perform? The circuit doesn't look anything special so wait and see. This example had been recently re-discovered and was in non-working condition, having been partially dismantled.
While the globe was off being re-chromed, the owner (obviously a man of taste, he arrived on a 1970 Harley Davidson...) brought the chassis round for me to look at. The mains flex was missing and the rectifier valves envelope had become separated from its base.
The speaker, with it's attached output transformer
came in a plastic bag with the volume control, some other small parts and service
information for it's cousin, the Model 100. That was an export model with a
slightly different valve line-up at the front end, so I hoped they were sufficiently
This chassis is circular, with the valves on the top and all the components underneath. The whole thing is much more robust than I thought, and quite heavy. This is probably how one of the valves became damaged, so to prevent the whole thing rolling around the main chassis plate was gripped in a vice.
A visual examination showed several faults. The wire from the HT smoothing coil to the screen grid of the 6V6G output valve had broken away from the valve holder tag, a 100pF mica capacitor connected to the aerial coils had broken away from its lead, and another de-coupler also had a broken lead, this time at the component body. These were probably caused by the unprotected chassis rolling around. The mains suppression capacitor (0.01uf) was only connected at the chassis end, it's other lead presumably connecting to the live switch connection.
Some old repairs were evident but the underside looked complete. Since this set was going to require quite a bit of work to re-assemble, I thought it prudent to check the mains transformer and output transformer for continuity, just to ascertain whether the job would be worth starting. Both tested fine, but a routine check of the mains switch revealed it to be intermittent open circuit and high resistance when operated. It was given a few belts from the Megger, which improved continuity no end! The mains cable and aerial come up the hollow tube support, and as can be seen are routed through holes in a thick washer fixed to the volume control shaft by grub screws.
I connected a length of wire to the remains of the aerial and a temporary length of 3-core mains flex for testing purposes.
The screen grid connection to the output valve was re-soldered and the broken Mica capacitor replaced with another from a scrap set. The tags of the volume control were cleaned of old solder and wire, before it was re-mounted on it's fixing studs with new 6BA nuts and star washers. It would of course be subject to vibration in normal use.
The wires were removed from the H.T smoothing electrolytic (making careful note of their positions) and each half connected in turn to the Megger. Both sections reformed perfectly over a few minutes, finally reading over 100k-ohms each. This was a pleasant surprise as initially I wasn't too hopeful, most other 1940's sets I have encountered have had capacitors which refuse to reform and need to be renewed.
The two other electrolytics on the chassis proved to be typical, both the 25uF cathode bypass for the output valve and the 12uF cathode bypass for the 6Q7G triode section testing short circuit. These were easily replaced by modern types. The former, a stud mounted type was left in position along with the wire to its positive end (cut below the chassis and bent over to hold it in position) to preserve the top view of the chassis. The speaker was also connected via extended leads to allow access to other parts, notably the volume control and mains switch. The coaxial cable from the diode detector to the "top" of the volume control had a rubber insulated centre core that was crumbling away, so I decided to change it to prevent future problems. Some modern braided screen co-ax was stripped of its outer sheathing (to preserve the appearance of the chassis), and a length of sytoflex sleeving slipped between the core and braid to cover the modern plastic insulation. A length was also made to connect the centre tag of the volume control to the 6Q7G top cap grid, which seemed a reasonable guess in absence of any other connection to it and lack of service data.
Most of the wax paper capacitors tested leaky, including the grid capacitor for the 6V6 output valve. I decided to replace them all anyway, in case any went faulty in the future and spoiled this classic set.
With the broken rectifier valve removed the mains was connected via the safety lamp and variac, the voltage slowly increased. The dial lamp started to glow, followed by three of the other remaining valves. The mains transformer rattled a bit at first but this stopped when it's mounting bolts were later tightened. The 6V6G was still unlit, with the mains voltage at normal. Ok, so it's a dud. Another known good spare was tried, which didn't glow either. Oh.
Six volts AC was measured at one heater connection, (with the other clip on chassis) fed from the other valves. Six volts AC was also measured at the valve's other heater connection which was supposed to be connected to chassis via a tag on the valve holder fixing screw. No voltage was measured across the heater. If the chassis side of the heater wasn't connected to chassis, no current would flow and hence no drop would occur across the valve heater.
The nut was found to be loose on the screw bearing the tag. With this tightened the replacement valve glowed normally, so was swapped for the original. That one proved to be OK too, lighting up normally.
I thought it prudent to check every nut and bolt on the chassis, and several were found to be loose. Those that had tags under them or were otherwise important had star washers fitted to prevent them coming loose again. (I wonder if it had anything to do with it's transport - all the nice girls love a Harley!)
Once the wax capacitors were replaced, a new rectifier valve was fitted and mains was re-applied. After ten seconds or so with the wavechange switch at MW and a few feet of wire connected to the remains of the aerial wire, a station was heard. A few came in up and down the band, local ones quite a lot stronger. LW and SW worked very well indeed, forcing me to turn down the volume when Radio 4 came crashing in! Unusually MW reception was worst, with only local stations coming in with any volume. I decided that I would risk alignment, as all valve voltages seemed reasonable.
In the absence of service data I had to guess at the IF frequency, but I reckoned that due to the age of the set and the valve line up (and general circuit design trends at the time) the I.F was most likely to be 465 or 470kHz. I followed the recommendations on Paul Stennings website regarding alignment. The signal generator was switched on and allowed to warm up, then with the set tuned to a dead spot near the centre of the MW band the signal generator was connected to the top cap of the 6K8G (mixer grid). An AC millivolt meter was connected across the volume control. Tuning the generator through 460-480kHz produced a small peak on the millivolt meter at around 470kHz. I wasn't sure which of the coils in the I.F coil can was the first, so each was turned carefully to see which one made the most difference. When I found the correct core and carefully adjusted it, the reading on the AC millivolt meter immediately increased, so much so I actually had to switch up a range.
When the generator was disconnected there was actually a distant station at what was previously was the dead spot. Seeing as I couldn't fit the tuning scale to the chassis I had no way of knowing whether it was accurate, but at least the radio worked reasonably well on MW now, bringing in a good assortment of stations across the band.
I won't push my luck, and hope the calibration
is satisfactory. Of course without the service information there's no way of
knowing whether the performance is "as good as it gets" or could be
improved. It is certainly acceptable given the valve lineup.
The chassis was left playing for some five or six hours while I concentrated on some D.I.Y jobs around the house. No problems showed up.
The new length of mains cable was fitted (but only after the volume control had to be re-fitted. I had forgotten to insert the wavechange tube) but as the switch was only single pole the neutral was taken to an insulated terminal post mounted on a protruding 6BA thread. This not only provided a neat joint, but provided a handy termination for the new mains de-coupling capacitor which was going to be connected across the switched Live and Neutral, instead of Live to Chassis as originally. If the customer had an ELCB this arrangement would be more suitable but still perform the same job.
The earth core in the mains flex was soldered to a tag fitted under a transformer mounting bolt, and then taken to another point on the chassis. The user has to wrap their hand around a metal column to operate volume and wavechange so I didn't want that connection to go astray! I also advised the user to have the earth (plug to case) continuity checked at intervals and enquired whether he had an ELCB fitted to his mains supply.
The aerial wire was extended by joining it to the original by an insulated connector block. This wasn't laziness on my part, but was done so that if the aerial became damaged (caught in the Hoover!) the user could easily replace it without having to remove the lower half of the globe to get at the solder connection on the wavechange switch.
Some readers may be dismayed at me not attempting to hide the modern components in such a venerable set. I am of the opinion that a working set is always better than a non working one, and in any case some capacitors had been replaced previously. A radio that doesn't work is just junk, whereas a working vintage radio is a thing of wonder. A person is much more likely to become hooked by this interesting hobby if they see (and hear!) a classic set working than not. Where does originality end? Just renewing the mains flex on any set renders it non-original....
The owner was certainly very pleased!
Text Copyright © 2003 Tim Pullin
Photographs © 2003 Tim Pullin and Jack Konynenburg
Diagram © 1988-2003 British Vintage Wireless Society
"Antiques Roadshow" video clip Copyright © 2003 BBC Television