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Old 15th Aug 2021, 2:23 pm   #1
PJL
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Default Eddystone 750 wreck

Rescued from the local carboot for £5, I am not familiar with Eddystone receivers but as it had plenty of valves including 5 empty sockets I concluded it was probably worth saving.

As you can see it is cosmetically challenged and as well as the missing valves, the outer case is missing, the tuning wire is broken, and I assume there should be a cover over the tuning coils.

I have got most of the missing valves in my spares, just an ECH42 to find. I will check the output and mains transformer continuity but are there other known problems with this model and is it going to be worth the effort?
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Old 15th Aug 2021, 2:31 pm   #2
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Default Re: Eddystone 750 wreck

Resistors are the main thing, if you get it sorted , they perform very well.

PS Why do folks store stuff in wet sheds??
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Old 15th Aug 2021, 2:49 pm   #3
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Default Re: Eddystone 750 wreck

I have one of these and it works extremely well. It is worth restoring. The metal cased 0.1uF caps are usually leaky and most are likely to need replacing. Also there are some "rat turd" capacitors attached to the valve holders inside the coil box that will definitely be leaky. To replace these you will have to remove the nearby coil(s). Tricky, but can be done with care. Best guidance for these sets is here http://eddystoneusergroup.org.uk/restoration-projects/ articles by Gerry O'Hara including 750 restoration tips and how to make a case. Mine was in reasonable condition so I didn't have to do so much. Apart from the tricky cap replacements the hardest task was re-stringing the dial. Even removing and refitting the front panel is a juggling act. Took me about 3 hours. Best of luck. P.S. I have plenty of ECH42. If you want one drop me a PM. Jerry
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Old 15th Aug 2021, 3:08 pm   #4
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Default Re: Eddystone 750 wreck

Mains and output transformers continuity OK and it looks much better after a quick brush as it was covered in a fine red dust - perhaps all that's left of the outer case although more likely roof tile dust...

Are the 12+ TCC 0.1 bolt-on paper capacitors likely to all need replacing?
Has someone got a picture of the coil screening plate?
I may have an X150 which is listed the same as the ECH42.

Replacing the fine wire dial cord looks like it will be fun...

PS: posted out of order!
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Old 15th Aug 2021, 3:15 pm   #5
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Default Re: Eddystone 750 wreck

Great find and save and well worth getting going again, fingers crossed that the mains transformer is still OK. Straightforward circuit (in double-conversion comms receiver terms) and workaday valve line-up. I have one here, possibly the favourite "tuning around" set and on most days- I did a fair bit of passives replacement and general overhaul and alignment on it but after that it's "just worked" for years. Even the main HT electrolytics reformed nicely, though I have a couple of 56uF 420V Rubicons "on standby". Whilst as a compact valve comms receiver it's a compromised set, IMHO it's a balanced compromise and less utilitarian looking than many comms sets- having 2x EF92 in the 85kHz IF strip might have given better shape factor and AGC performance than the single 6BA6 but then one can spend all day picking holes in a compromise....

Definitely agree with all that Jerry cathoderay57 says- lifting the appropriate coils out in order to change the little brown 'unts might seem a pain but it's actually quite quick and easy in the end. I was going to offer ECH42s but looks like he beat me to it! The coil-box cover is just a sheet of appropriately-drilled ally, the cover over the gang capacitor shows that it's a later production version. The chrome handles should polish up nicely and the finger-plate looks good- mine suffered "fractal cauliflower" corrosion during its previous neglect.

Colin
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Old 15th Aug 2021, 3:38 pm   #6
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Default Re: Eddystone 750 wreck

Quote:
Originally Posted by cathoderay57 View Post
. It is worth restoring. The metal cased 0.1uF caps are usually leaky and most are likely to need replacing. There are some "rat turd" capacitors attached to the valve holders inside the coil box that. Also they will definitely be leaky. Jerry
I guess those might be the pesky little bright red oval ones, about the size of a cod liver oil capsule?

I went through an Eddystone phase and had about eight models at one time in the eighties, (680X, 940, EA12, EB35 etc). Those little red blighters seemed to abound. The coil packs, 'switchery' and anti backlash tuning was a joy to behold. The EUG are a great bunch - I subscribed to 'The Lighthouse' when Graham Wormald was still alive. The EUG has been online for some years now and there is just so much info free of charge and lots of help from guys who know the radios inside out.

For anyone who doesn't know, the story of how Eddystone Radio came about is fascinating: A change in women's hairstyles in the early 1920s to bobbed hair, ('pageboy' style), leading to the collapse in the market for hairgrips, which overnight reduced Stratton's market for hairgrips from six tons to one, resulting in diversification into radio components, and later, radios.

In Feb 1994, forum member ChrisG0EYO (Chris Pettit), who was then MD of Eddystone, (and is Webmaster for the EUG), wrote a history of the company which was published in Feb 1994 PW Magazine. The link to the article can be found here:

http://eddystoneusergroup.org.uk/his...dystone-radio/

Loads of info on the EUG on the 750.

For example, Gerry O'Hara's 47-page 2006 article including the manual here:

http://eddystoneusergroup.org.uk/Res...%20Article.pdf

And Gary Abach's 2019 8-page article here:

http://eddystoneusergroup.org.uk/wp-...FINAL-v1.2.pdf

Hope that's on interest.

Good luck with the 750.
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Old 15th Aug 2021, 3:43 pm   #7
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Default Re: Eddystone 750 wreck

Those TCC capacitors? Every one! replace the lot. Little time-bombs. If any are still OK, they won't last. And those brown hunts capacitors kept the families of many repairmen clothed and fed for a couple of decades of the radio and TV repair trade.

An RF cover plate is easy. Thin aluminium and a load of holes for access to the coil slugs and the capacitor trimmers. make a paper one (or two or three) first to get the positions right. The most work is in labelling the holes. Know anyone with a letter/number punch set?

These are a reasonable set. A bit fast tuning for SSB and CW. The gain is a bit low overall, but with modern noise floors you'll find it less of a limitation.

Compared to a domestic receiver with shortwave bands, this is a step or two up. It's a rung or two below the later professional receivers, but Eddystones are all gorgeous lookers. If you're a radio person, you have to have an Eddystone somewhere currently, or in your past. Mine's an EA12.

The tuning wire is very fine multi-stand steel. Look on the Eddystone users group to find sources.

For the black crackle paint, search the MG owners club website.

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Old 15th Aug 2021, 4:21 pm   #8
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Default Re: Eddystone 750 wreck

I've attached an image showing the coil box cover and a sketch labelling the metal-cased caps below decks. Of these I replaced C66, C79, C50, C24. C55 had already been replaced. The other snag I had was a dodgy BFO. Rat turd caps at play again https://www.vintage-radio.net/forum/...d.php?t=174605. Cheers, Jerry
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Old 15th Aug 2021, 4:51 pm   #9
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Default Re: Eddystone 750 wreck

While you're at it you might be able to help me out. I was prodding about (having opened mine up) and I noticed a strange component value. It is R54, the HT dropper for V2 hexode anode. In the early version of the circuit it's listed as 1.4k and in the later 1.5k. It is a half Watt component located outside the coil box connected between the HT supply and the inner rear pin of the 1st IFT (located front corner of chassis). The thing is - mine has a 150 Ohm resistor fitted that measures 200 Ohms in circuit. It looks original. What has yours got? On second thoughts it appears to have got hot in the past, probably owing to a leaky C86 paper decoupler (since replaced). The 3rd band is burned and although it looks brown now, it might have been red originally. Odd that it has reduced in value by a factor of 10 though. I think I'll fit a replacement 1.4k. Cheers, Jerry

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Old 15th Aug 2021, 5:38 pm   #10
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Default Re: Eddystone 750 wreck

Marked as 1.5K and measures 1.39K in circuit. It is old style markings with brown body, yellow tip and red centre band.

You still seem to have plenty of the 0.1uF bolted capacitors in play?

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Old 15th Aug 2021, 6:21 pm   #11
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Default Re: Eddystone 750 wreck

Check the Selectivity Max/Min switch for mechanical issues and that the upper coils in each of the three IF cans raise and lower correctly when the switch is operated and are not stuck or broken.
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Old 15th Aug 2021, 6:36 pm   #12
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Default Re: Eddystone 750 wreck

A double conversion set I believe. My worked very well last time out and due for another power up. Along with the EC958, EA12 plus others !
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Old 15th Aug 2021, 8:24 pm   #13
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Default Re: Eddystone 750 wreck

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Originally Posted by HamishBoxer View Post
A double conversion set I believe.
1st IF = 1620 kc/s; 2nd IF = 85 kc/s. The general coverage 750 concept and circuitry led directly to the 888 with bandspread amateur bands and then the 888A with a product detector. The high 1st IF frequency did wonders for image rejection, while the low 2nd IF did wonders for the selectivity. The 750 looks to me like a 640 (IF = 1600 kc/s) with a BC453 Q-fiver all in one box - but much prettier. Revolutionary for the early 1950s.

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Old 15th Aug 2021, 8:24 pm   #14
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Default Re: Eddystone 750 wreck

My early production set (seemingly July 1950) also had the 1.4k V2 anode feed in half watt ceramic body BTS- the nature of its usage makes the exact value utterly uncritical, with the low (1-2mA typical) anode current of hexode/heptode mixers anything from 1 to 5k or thereabouts would do the job. I can only think that the value concerned came as a barrow-load of surplus from some source and Eddystone put it to use in an appropriate place. The AF amp decoupler feeding the 270k anode load is a 25k component of a similar type, again an uncritical value that might have been a "sweeping". Another oddity is the tone-correction capacitor across the output transformer with the curiously precise value in both component list and practice of 1425pF 2%- this component is surely one of the most subjective value choices in most radios. On a hunch, checking the component listing for the 640 (effectively the 750's predecessor) reveals an oscillator padder for one band of 1425pF 2%.... In other words, it's something of a smorgasbord of what was around at the time.
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Old 15th Aug 2021, 8:40 pm   #15
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Default Re: Eddystone 750 wreck

Quote:
Originally Posted by PJL View Post
You still seem to have plenty of the 0.1uF bolted capacitors in play?
Thanks for the update - I meant to say I'll fit a 1.5k which is obviously the preferred value. Some of the metal cased 0.1uF caps have been restuffed - wasn't worth the effort frankly so I gave up and started fitting naked yellow polys. Cheers, Jerry
P.S. I've attached a scaled image of the coil pack cover that you might be able to use as a template. There is a fifth screw in the bottom RH corner but the image is too dark.
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Old 15th Aug 2021, 9:30 pm   #16
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Default Re: Eddystone 750 wreck

You should find a date on the 2 main electrolytics. One of mine is dated July 1956 and the other September 1958. Mine is missing the shield box over the tuning gang with the equipment label and so I don't know what the Ser No is. Jerry
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Old 15th Aug 2021, 9:43 pm   #17
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Default Re: Eddystone 750 wreck

Whilst the set has obviously suffered from damp topsides, hopefully the tuning gang cover should have limited condensation/dust on the gang vanes and contacts. Anyone who likes mechanisms will appreciate the ingenious variable-ratio arm arrangement attached to the front of the tuning gang that engages with a brass peg on the final gear and makes the tuning scale almost linear, as opposed to the HF-end cramping familiar on many tuning scales. I note that the rust on the PSU chassis section implies that it is mild steel, on my early set it's plated brass, perhaps the heavy transformer could distort it and a change was made to steel?

The previous owner may have mislaid the outer case but at least they bothered to nest the associated screws....
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Old 15th Aug 2021, 10:05 pm   #18
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Default Re: Eddystone 750 wreck

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Originally Posted by HamishBoxer View Post

PS Why do folks store stuff in wet sheds??
Probably not a wet shed per se but heavy chunks of metal will attract condensation which causes the selective rusting seen. When stored away, perhaps in the summer, the shed would be perfectly dry, come autumn, long cold nights followed by warmish damp days......
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Old 15th Aug 2021, 10:16 pm   #19
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Default Re: Eddystone 750 wreck

Serial number is E00948, one electrolytic is March 52 but the other looks identical but has different markings without a date. I noticed the audio coupling capacitor has fallen off the pot which might have led to its consignment to the shed/loft as it looks a major exercise to solder it back.
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Old 16th Aug 2021, 11:17 am   #20
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Default Re: Eddystone 750 wreck

Passed it's first test of restorability as the knobs came off readily. Choke continuity OK, ordered pike wire and some caps so ready to go. I have a couple of questions:

I have the service manual but is there a component layout drawing?

I am still unsure of the capacitors to replace before powering up as the ones around V1-V3 are difficult to see, I have ringed one in the attached. Looking at the circuit, the caps around V3 are C27 and C28 heater decoupling and listed as 0.0005uF moulded mica.

I would also appreciate advice on which coils to remove, do I take out a whole bank?
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