EDDYSTONE 940 Deaf?

[Tim]

Hi all.
Have one of these in at the moment which the owner suspects might be slightly deaf. Presumably, as this is a coms receiver the dial should be packed with stations!
What should I expect with say 10-20 ft of aerial connected to A1 ONLY (A2 is grounded. ) Presunably it should be capable of receiving some distant stations on MW(Radio Scotland, Devon air and Chiltern radio are receivable here in wiltshire on ordinary radios, albeit feintly) but not sure it does.
As this receiver is designed for a balanced aerial, would some sort of balun help?
Haven't really looked at it yet, but some pointers would help.
Have circuit.
Thanks
Tim

[Skywave]

Hi Tim,

First, the aerial connection.

I believe that the aerial / earth connections on the 940 are the usual Eddy arrangements of A1, A2 and E. For a LW-type aerial - such as what you are using - connect the aerial to A1 and jumper A2 to E. Then connect E to a good earth.
Aside: If you are using a balanced aerial, say a dipole with a balanced feedline, you connect the feedline to A1 and A2. An earth connection to E then becomes optional.

Secondly, sensitivity.
The Eddy 940, when working correctly, is a very sensitive receiver. It features two RF stages; single conversion superhet. With the aerial that you are using, you should have no trouble at all in picking up local - and not so local, signals - on MW at a good strength, and other, more distant signals at an easily "listenable-to" level and quality.
On the other freq. bands, up to about 14 Mc/s or so, you should receive a good range of signals, especially in the SW broadcasting bands, at good volume.

You may well have a "slightly deaf" Eddy on your hands. Not uncommon.
Generally, Eddy. receivers respond quite well to the classic approach to fault finding on valve receivers. To the inexperienced, when the covers are off, they can look a bit daunting. Don't let this put you off.

In detail:
start by using the Test Kit that Mother Nature gave you! Is it insensitive on only one band, or all bands? Do all of the operator controls work - especially the RF gain? Are all the valve heaters glowing? Remove each valve - especially the RF amp. valves - and check for dirty / corroded pins. Have a general look around underneath the chassis. Check for the usual culprits: overheating resistors, leaking caps., etc.
If no faults found after this, you need the circuit diagram. The 940 is quite common, so getting a copy of this should be quite easy. Next step is the classic "are the d.c. voltages correct" at the valve sockets? All Eddy. cct. diagrams list the voltages at the valve pins for correct operation.

At this point, if you haven't found the culprit, you should be well on the way.
It's quite rare for Eddys. to develop obscure faults in the "deaf" scenario, and perseverance nearly always pays off.

If the problem is restricted to only one band, then the band-select wafer assy, is suspect. A squirt with switch cleaner usually does the trick!

Obviously, if you have the test kit available, you can measure the sensitivity & S/N ratio - but this is rarely necessary to locate the cause of a "deaf" Eddy. Useful though, to confirm that all is well after a servicing session.

Keep us posted on progress.

Al.

[Brased]

Originally Posted by G8DLH

If no faults found after this, you need the circuit diagram. The 940 is quite common, so getting a copy of this should be quite easy. Next step is the classic "are the d.c. voltages correct" at the valve sockets? All Eddy. cct. diagrams list the voltages at the valve pins for correct operation.Al.

If you haven't already found it, the BAMA website bama.sbc.edu has a copy of the instruction manual which includes the circuit diagram and basic servicing information.

Good luck!

Edward

[Tim]

Had a quick look at this one today. Shows signs of previous repairs, a few resistors and capacitors. Most of the original resistors over 33K are high or open. Changed all those I found. Audio now much better.
Only seems to receive Five live, but with constant whistle. One would think the MW would be packed on a set like this! RF gain does work, but only really right at the top.
The underside of some of the valve sockets are extremely difficult to access. Does the coil bank come off, cos I think I have some faulty 100 K resistors down there somewhere.

ECC189 tests OK.

[Skywave]

I would strongly recommend NOT dismantling the coil bank in order to gain access to the valve socket pins. You can easily give yourself major headaches doing this!

I'm afraid that all Eddystone valve radios can be a bit of a pain to do maintenance on sometimes - mainly a question of access - as you seem to have discovered!
'Fraid that here's no easy way round this: a lot of patience, time, experience, manual dexterity and skill is required.
If all else fails, you could try contacting one of the service & repair organisations as advertised on the Edystone User Group Website and ask for a repair quote

Al.

[Tim]

I would strongly recommend NOT dismantling the coil bank in order to gain access to the valve socket pins.

How on earth did they make it that way in the first place! It's ludicrous!!

If all else fails, you could try contacting one of the service & repair organisations as advertised on the Edystone User Group Website and ask for a repair quote

I am the repairer! I could always sub it out I 'spose!
I haven't tested the other valves yet, or got the sig gen out looking for the low gain section.

My sig gen, although fairly stable isn't crystal controlled. Would it be sufficient to calibrate the sig gen against a crystal calibrated frequency counter?

Ta
Tim

[Skywave]

Originally Posted by Tim

How on earth did they make it that way in the first place!
Tim

I'm assuming that the 940 has a mechanical assy. that is typical of Eddys. of this vintage, where there is a die-cast coil box in the the centre of the chassis with the band-switch running through the centre.
It was made this way by fitting the valve holders in first with their associated components, then the band-switch, then the coils.
Why it was made this way I don't know - but it does provide for very short, direct connections between the valves in this section, the band-change switch, the coils and the tuning condenser. All very necessary to achieve the required performance.

Like I say, Eddys. of this vintage can be a bit of a pain to fault find on because of access issues - such as this.

As regards your sig gen, it doesn't need to be crystal controlled to attempt to measure the gain of the receiver. (For re-calibration of the oscillator, desirable but not a pre-requisite). It's more important that is has a decent, reliable attenuator. However, having said that, judging by the fault conditions that you have described, the logical place to start the fault finding process is in measuring valve electrode voltages.

Which is where I came in.

Good luck.

Al.

[Tim]

I think voltages are about right. I only have a small circuit diagram, and published voltages are also in small print, so they tally with what I think they are.... .I'll see if I can find a larger diagram or blow up the one I have.
Thanks for your help. Given my understanding of Murphy's law I can guess where the fault is gonna be!