Eddystone EC10

[Wendymott]

Hi peeps.. Here is a description of my current project, which is nearing completion. As I have two EC10's the first was a survey of what was going to be needed and what could be possible. The first EC10, was "siliconised", but in PNP types, to maintain the polarity of the main IF assy. The OC171's were replaced with BF960 types. The bias resistors were changed to suit the new devices, and all carbon film resistors replaced. To be honest on some ranges it is a bit "lively" and oscillation can happen. But at the moment I have no need to alter this. The EC10 whilst being a full range HF receiver, is VERY limited in bandspread. I added the Varicap modification of the MK2 which does help, but the amateur bands are still very cramped.

Thus EC10.2 was started. I have produced some photo's to show the project in its evolution.
First I needed to replace all the I.F strip with something a bit more modern. This involved the Plessey SL612, IF amps, SL623 AM/SSB detector, a 455Khz / +/- 2,5Khz filter, and a 200 hz +/- 50 hz audio filter.
Yes I know........ the SL series is over 30 years old, but as I have some and know how to use them it was a "no brainer".
Two SL612's are used in the I.F amp with a Toko IF trans at the front for matching. The SL623 is used in conjunction with a SL612, for SSB AGC. Two dual op amps form the four pole audio filter which is switched in and out.
The audio amp is the LM386.
The RF section has been severely modified with 2 x Dual gate mosfets as RF amp, Mixer and a BFY90 for the local oscillator.

The tuning gang was removed, see photo, and a 100K pot put in position to control 3 x BB119 Varicap diodes.
It is unfortunate but at present the two LF bands are not working, due to the inductor/capacitance ratio not being correct, but as I want this receiver for 40, 20. 15 and 10, it is of no consequence. On 40 metres the scale length between 7.0 and 7.2 Mhz is now approx. 6", on the 28 - 30 MHz range it is full scale. I will need to rewind the range 4 coils for 15 metres.

The Loudspeaker was in a bit of a state so that has been replaced, see photo's, and the Tuning dial has been totally revamped. I removed all the paint from the dial glass, painted the scale plate white, added a "S Meter", and generated a Scale artwork on my CAD software. At present the frequency's have not been marked on, but I removed the glass to enable me to mark the scales, then transfer to the CAD, for a new scale to be produced.

A new fingerplate was made to hide the rectangular hole from the eddystone push button switches. Toggle switches were added to ensure reliable operation, the original buttons were showing their age.
Sorry but I have no room for the finger panel. But will include on next posting.

Oh yes the tuning knob was turned from a piece of ally bar,,,,,, feels much nicer.

Yes I know............ the purists will be shouting at the PC...... sacrilege...but in my view a device not working to as good specification as it can be, is not worth having.

In a few days the final version will be complete.......... if anyone has any ideas , please feel free to comment.

[Wendymott]

Here is finger panel ..... schematics and the IF pcb.

[dave walsh]

I don't know about the purists but I used to see people scooping these up 15/20 years ago at Rallies. It seemed clear that they were out to make a killing as they had a high re-sale value at one time being both sought after and compact.

You seem to have take a rather rough one and used your expert knowledge to soup it up to a much improved spec. Can't see a problem with that and it would be good to see the finished item. Might be better than the original. Eddystone once sent me a Blueprint of the circuit when I wrote [as a student] enquiring about this unusual transistorised comms set-don't have it now or you would be welcome. I can't say that they have ever appealed to me that much but there's clearly a following.

For some reason this [rather more comprehensive] restoration reminds me of the first James Bond book where he takes a Bentley that's been rolled on the Dover Road. and has it cut down to a small grey sports car but with the original supercharged engine. They should have put that in Dr No!
Dave W

[Radio Wrangler]

Wendy,

With varactor tuning, you could have put individual diodes on each coil, rather than switch the same diode to the coil in use. This way you could use different diodes or multiples to fiddle with the L/C ratio on a band by band basis.

David

[Herald1360]

This all sounds not so different from an R1155 with proper BFO, product detector, PSU and output stage instead of the DF bits in the late '50s. No doubt in a few years it'll be worth much less than an unmolested one, but it'll still be a much better receiver.

[Radio Wrangler]

I must admit I had mixed feelings, too. But I've never placed much value on the EC10. I always felt it was a nice cabinet and drive, wasted. Why they commanded such prices on the second hand market beats me... a sort of triumph of cuteness over function.

David

[Bazz4CQJ]

Seems like a most excellent project to me; boo-hoo to any purists who might be disdainful. My HRO is currently undergoing what I like to describe as a "mid-life update" and I will have to take a closer look at Wendy's EC10 to see if there is anything I can usefully copy .

B

[Wendymott]

Hi Guys. David, I did consider using separated Varicaps for each range, but I am not interested in top band or 80, "excuses for not getting it right"...........but as it is an "ongoing" maybe. The stupid prices of EC10's on ebay, I cannot understand it either... I paid about £50 each and that's my limit...a tidy Mk2 went for well above that last week. As far as I was concerned my second buy was to do what I am doing now, and the case and drive will be the only original items. The general coverage one will get the same electronic treatment, except for the tuning cap.

Thanks for the comments...

[HamishBoxer]

Well better working and non original than non working.

Nice job, EB35s go for about half what EC10s do on ebay. Same drive. box etc. (well near enough).

[Wendymott]

Just a note about the coils. I know they were not made to be "messed about with", but the through hole pins on the bottom of the coils are totally none serviceable. Even with great care they seem to break on the bend over. Plus the pin mount is polythene, so multi soldering is not an option. As I am rewinding some of the coils, I have decided to make new pin mounts out of pcb material with copper removed.
Onward and upward...

[Tyso_Bl]

I really like what you're doing over there, a very different aproach to sorting a radio. I'd love to see/hear the results perhaps via youtube if that would be possible when done.

[Skywave]

Originally Posted by Radio Wrangler

I must admit I had mixed feelings, too. But I've never placed much value on the EC10. I always felt it was a nice cabinet and drive, wasted. Why they command such prices on the second hand market beats me... a sort of triumph of cuteness over function.

Yes, I know where you're coming from with those thoughts, David. But please bear in mind that at the time when the EC10 was presented to the market, Eddystone were under intense competition from the Far East with similar specified radios - e.g. Trio / Lafayette / Kenwood / Star, etc. The only substantial edge that Eddystone had in that specific market-place was the name, Eddystone - and the assumed reputation for quality that went with that name. However, as regards performance, my sad experience is that the EC10 does leave a good deal to be desired and I was not impressed with the internal construction, either.
As for the prices that they fetch on the second-hand market, two factors spring to mind: appearance and the name, Eddystone.

Al.

[Wendymott]

As I mentioned earlier, it's now an Amateur band receiver for 40, 20, 15 and 10. Forget about the WARC bands.

So I have unwound the "80 metre" coils and rewound for 15 metres. However the location of these coils is second furthest from the switch. So now all the coils i.e 40 and 20, need moving one location away from the switch, to minimise frequency drift on 15 due to longer wires. All the wires will be then held firmly, not relying on their natural rigidity.

However, Eddystone, in their infinite wisdom, swapped two of the pins of the "80" osc coil, so a direct transplant was not easy. Fortunately the other coils are the same pin outs.
Another thing to note is if anyone is mad enough to copy my suggestions, when fitting a variable pot instead of a tuning cap, do NOT endstop the pot - start rotation a few degrees from the end. As the resistance changes, the voltage change is a bit lumpy. Moving the start point by a few degrees helped enormously.

[Silicon]

The tuning potentiometer could have a big influence on the feel and reliability of the radio.
Did you use a carbon or plastic film track version?

[Wendymott]

Hi Silicon, I was thinking about this very thing today with a view to a heavy mod on Monday. The 100K pot is WAY too high, as the slight change in rotation will give a much larger voltage change at the bottom end, and this is where the capacity change of a Varicap is greatest. The value of the pot will be reduced to 5k, thus the resistance change to rotation ratio will be much reduced.
I also invested in some new varicap diodes, with a 50% increase in range, this was because the 10 metre band was not covered fully (1.7 Mhz) because the BB119's were a quite small change in capacity. This means the overall bandspread is reduced on say 40 metres and 15, but I have now a spare switch wafer, which will allow me to reduce the applied voltage to the bands that have a reduced bandspread, thus I can have full scale on all bands if I adjust the voltage ratio's correctly.
To answer your question, I bought a Plastic film version, but I found the carbon tracked one seemed nicer.

[Radio Wrangler]

I've got a few high resolution 10-turn pots kicking around if they're any help.

David

[Wendymott]

Hi David. Thanks but no thanks, it would be so difficult to integrate into the Eddy dial mechanism. As it is the pot I am using only rotates 180, and I like the feel of the current mech.
Another thought I did have is this. Use a Dual gang pot in parallel, this would reduce any "Blind" spots. I am going to test later.
Also I am thinking that maybe a log pot may help the none linearity, but its not really important. It's something else I am going to test today.
Another thought, is to make the long wires that connect the inductors to the switches, into a pcb. I have already made an EMC shield to cover the osc and mixer coils, I will post a photo later.
Its getting there.

[G6Tanuki]

Originally Posted by Wendymott

Another thought I did have is this..............Use a Dual gang pot in parallel, this would reduce any "Blind" spots........

That's standard procedure in a lot of industrial applications - the two pots are wired in oppositon (so one generates a rising output voltage as it's rotated the other a falling voltage).

The two voltages are then fed to a pair of op-amps (one inverting, one non-inverting) and the outputs are combined to generate the desired output.

[Wendymott]

Hi Tanuki..... Well after an exasperating day , one of my 2022's failed, thus me thinking the tuning was not going as expected. In my case, the thought was, that if one track was noisy in a particular place, the other would cover it, and I wired them in parallel, not in antiphase as you suggest.. however it is a good thought for later. The log pot was not an option, it stretched the LF end and compressed the HF end. And I bet you cannot get Antilog pots anymore.......... someone will prove me wrong, but its now 2 x 100K linear in parallel. I have also introduced "trim" pots into the Varicap pot feeds to enable me to get a reasonable dial length on all 4 bands. I found I had a spare wafer on the band switch. Another addition is a 1uf non polarised cap on the slider of the Varicap pot to reduce any track noise.
More later