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Old 16th Jul 2018, 12:30 am   #21
space_charged
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Default Re: IF fault on Eddystone 770R

Thanks Skywave for your encouraging complements.

In fact, its in fairly good shape now. I think the sound stage needs attention, it may be a bit distorted. I have aligned the FM ratio detector (using the wobbulator method) and it behaves as expected and looks quite good (linear) over the required deviation range.

I've taken a few photos of it, including the IF strip of course, on the bench attached to the test equipment. Overall its in quite nice condition.
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Old 16th Jul 2018, 12:35 am   #22
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Default Re: IF fault on Eddystone 770R

A few more photos of the 770R showing the turret tuner and the condition of the biscuits. I gather they are often a problem in these sets, but in this set they seem OK.

I am still monitoring the IF gain to see if there is any sign of the fault, but none seen so far.
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Old 16th Jul 2018, 12:51 am   #23
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Default Re: IF fault on Eddystone 770R

I must admit that the yanks do make a beautiful wireless!!!
You are right!! It's in very nice condition.
Removing the whole IFT looks like major surgery however.

Joe
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Old 16th Jul 2018, 9:25 am   #24
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Default Re: IF fault on Eddystone 770R

Quote:
Originally Posted by joebog1 View Post
I must admit that the yanks do make a beautiful wireless!!!

Joe
I've no doubt they do, but Eddystone are a British company.

http://eddystoneusergroup.org.uk/his...dystone-radio/
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Old 16th Jul 2018, 6:46 pm   #25
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Arrow Re: IF fault on Eddystone 770R

The photo #5 in post 21 - the underneath of the chassis, IF strip - looks different to what I found in the 770R that I had - as per my photo below. In yours, there seems to be a good deal more space to get the tools in. But how you are meant to gain access to components at the rear of the chassis, I have no idea - they're simply buried!

Al.
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Old 16th Jul 2018, 6:54 pm   #26
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Default Re: IF fault on Eddystone 770R

Thanks Al for the photo of your 770R. I'd say that is exactly the same as mine. Remember that there is side access as well as bottom. The difference is probably the way I took my photos. Also I used a fairly wide angle lens quite close up too.

The AF output stage is much narrower and there is no side access. I'm looking forward to working on that. Even doing voltage and resistance checks will be a "challenge".
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Old 16th Jul 2018, 7:01 pm   #27
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Default Re: IF fault on Eddystone 770R

Excellent work sir .
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Old 17th Jul 2018, 6:41 am   #28
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Default Re: IF fault on Eddystone 770R

Oops!! My apologies, but I have always thought ( wrongly) that Eddystone was American.

I have never seen one "in the flesh".

Joe
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Old 17th Jul 2018, 11:42 am   #29
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Default Re: IF fault on Eddystone 770R

Eddystones have quite a following in Blighty- they are sturdily and neatly constructed but were arguably a bit behind the curve in their electronic aspects. In a way, I think that that explains their popularity- they have generally survived more-or-less intact and the hobbyist who might have been frightened of the complexity of an RA17 or an R390A is quite at ease with a 730. TBH, I think that the combination of unadventurous design and the high price for what was offered would have sunk them long before it did if it hadn't been for military and government orders, also the market for sturdy and straightforward cabin receivers. They were a relatively small operation and used a limited range of basic front-panel castings and outer case foldings- e.g. the same early '50s front panel design served everything from the very basic facilities 670A to the quite sophisticated and complex 910. That meant close-packing of switches and the use of co-axial controls in the swankier models. As mentioned, it also meant that some sets became very crowded inside- the 670A here is very easy to work on, a bit like a well-made domestic set, but the 750 with the same size case but double the number of valves and a chunky mains transformer takes a good deal more care over maintenance and component replacement. And it's by no means the most closely-packed of Eddystones!
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Old 17th Jul 2018, 11:57 am   #30
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Default Re: IF fault on Eddystone 770R

Thanks turretslug,
I did offer apologies, BUT I have never owned an English radio.
I have ( in the dark distant past)owned some very nice African short wave only sets(apparently from some tank used there, using loctal vales) covering the lower HF bands. I have also owned a couple of Japanese sets, BUT they were modern using miniature 7 pin valves.
English no!
I have a mark II Avo valve tester, and I absolutely love my Avo model 8 MKII meter. I did have a few Marconi test pieces that I scrapped as they had been at the mercy of the tropical north Queensland environment.

I did notice that the wiring was very similar to my valve tester, or some H&H guitar amplifiers. Superbly done!!.
Thanks for the answer, in any case


Joe
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Old 17th Jul 2018, 1:39 pm   #31
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Default Re: IF fault on Eddystone 770R

Thanks Turretslug. You seem to know your Eddystones.

Perhaps you can enlighten me as to where the 100pf resonance capacitors for the IF transformers are in a 770R?

I have a 680X as well as the 770R. I first used a 680X at the school Radio Club which was run by Mr Simpson, the technical drawing and woodwork teacher. The 680X was in the radio shack and I could get my hands on it sometimes.

Eddystone was a Birmingham company and I live about half a mile from the Stratton Works site. Its now a housing estate.
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Old 17th Jul 2018, 2:13 pm   #32
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Default Re: IF fault on Eddystone 770R

Wouldn't really claim to know them- jut the few that have passed through my hands, I find industrial design and the "fingerprints" of different designers and manufacturers interesting and Eddystone are one of the more distinctive examples.

I'm afraid that I know nothing about the 770R- I had followed threads here and elsewhere on it, but don't really have an interest in VHF general coverage (I've a rarely-used compact VHF/UHF solid-state synthesised receiver anyway) and the consistent remarks about its very tricky access and maintenance had put me off anyway! I can certainly believe that it would be very close-packed from the circuit and valve complement.

Good luck with the IFT quandary- I'm intrigued to know the answer.
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Old 17th Jul 2018, 2:19 pm   #33
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Default Re: IF fault on Eddystone 770R

Maybe tucked away in the IFT base somewhere?

Lawrence.
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Old 17th Jul 2018, 4:55 pm   #34
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Default Re: IF fault on Eddystone 770R

Thanks Lawrence for your suggestion. I think that must be the answer. I may try to get a spare transformer, if only to confirm that without risk to my 770R.
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Old 17th Jul 2018, 5:33 pm   #35
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Default Re: IF fault on Eddystone 770R

The capacitors are indeed mounted inside the IF can as can be seen from the attached. Capacitors are polystyrene 100pf 125v, and are mounted across IF can pins 4 & 6, and 1 & 3.

I completely rebuilt my 770R Mk1 some years ago and took many digital photo's together with drawings to ensure it all went back together correctly. To rebuild the audio unit I removed it from the main chassis. It means cutting into the wiring form and removing a few bolts, but so much easier to get at all the components. I am still using the receiver together with a rebuilt 770U Mk1 and EP14 Panadapter.
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Old 17th Jul 2018, 6:04 pm   #36
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Default Re: IF fault on Eddystone 770R

Thanks bc312 for the photo of your IFT.

The problem is that I have removed the screening can of the IFT and still can't see any capacitors. I expected to see exactly what is in your photo but I don't.

My 770R seems less sensitive on range 1 (highest) than the other ranges. Also there is a bit of frequency drift for a while after it is switched on. Are these "features" or a fault would you say?
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Old 17th Jul 2018, 6:56 pm   #37
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Default Re: IF fault on Eddystone 770R

Capacitor mystery solved, I think. There are definitely NO caps soldered between the vertical wire rods. The TOP of the assembly is marked 100 +/- 5%. I think the top plate has the caps built in to it and they are across the rods at the top. See the photo attached.

Looks like the IFTs in my set are a different type and don't have discrete caps.
I'm sure that there were variations in components during manufacturing history of the 770R. If it helps/interests anyone, the serial number on my set is G10693.
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Old 17th Jul 2018, 7:41 pm   #38
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Default Re: IF fault on Eddystone 770R

Goodness, that's cunning! Neat, too- I suppose it makes for efficient assembly on a mass-produced item, but hinders someone without access to the original type spares or who comes to a set decades later.... I'm sure something rings a faint bell about some American design that uses something a little along these lines- after all, they were the experts in facilitating quantity production.
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Old 17th Jul 2018, 8:01 pm   #39
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Default Re: IF fault on Eddystone 770R

Similar types were used in American production, they did give problems.
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Old 17th Jul 2018, 9:56 pm   #40
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Default Re: IF fault on Eddystone 770R

It looks like I'll probably have to replace all the top assemblies with built in 100pF caps. I have done just one IFT. The caps are built in to the top paxolin square. That is needed to hold the innards of the IFT in place so can't just be removed. Its made up of layers and careful use of a small hacksaw allows the silvered mica plates to be removed. Then the cleaned up plate is re-soldered and two 100pF silvered mica caps soldered in just below the paxolin. The resulting increase of gain is spectacular. Once all four IFTs are done there will be much more IF gain.

I know they are supposed to be 100pF "silvered mica" from the service manual.
Like to know if anyone any advice on what sort to buy?
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