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Old 1st Nov 2008, 1:28 am   #21
Skywave
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Default Re: Eddystone 640

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peter.sables:
For my next project I've picked up a "not bad" Eddystone 640. Is there any pitfalls with this set that I should know about?
Pete
---------------------

Yes - I just thought of another! A maintenance / safety issue.

If the HT is switched off (front panel) and then if the a.c. mains switched off (again, front panel), the charge in the PSU reservoir cap. (C72) remains intact: there is no bleeder resistor! My fix is to install a 47k-ohm 5-watt resistor across C72 to provide a discharge path.

I have had two examples of C72 being s/c; one of these had a failed FW rect. as a consequence. As I mentioned previously, there are no fuses in the PSU The physical & mechanical layout beneath chassis does make the fitment of such an easy task

Aside: Quote edited by Skywave: "Edison" replaced by "Eddystone".

Al.

Last edited by Brian R Pateman; 1st Nov 2008 at 7:45 am. Reason: Quote fixed.
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Old 2nd Nov 2008, 8:04 pm   #22
peter.sables
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Default Re: Eddystone 640

ha a problem.

On looking at my 640 it HAS been modded.... What should I do, the mod works and its been well carried out.

ho dear, ho dear....

Pete
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Old 2nd Nov 2008, 9:06 pm   #23
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Default Re: Eddystone 640

HI.

This is just one mod. to my 640. What was on his mind and is it worth keeping!.

Pete
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Old 3rd Nov 2008, 12:38 am   #24
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Default Re: Eddystone 640

Peter,

The fact it has been modified obviously concerns you so just put the circuitry back to what it should be.

The Set is yours and it is entirely upto you what you do with it.

Personally I will only mod a set if it improves safety or restores functionality.

I have a Collins R390A after 60 years the collins IF filters good as they were just deteriorate to eventually a point whereby they do not work. It is no good fitting replacement NOS as the degradation is not through use but through the deterioration of the inner materials of the filters with time.There are some modern replacement filters available which out perform the originals and are designed to physically replace them. The specs are different but bandwdths are more suited to modern comms.

Purists may have their own views on that but I like to use the gear and I want it to work safely and reliablly.

Mike
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Old 3rd Nov 2008, 1:56 am   #25
Skywave
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Arrow Re: Eddystone 640

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Originally Posted by peter.sables View Post
HI.

This is just one mod. to my 640. What was on his mind and is it worth keeping?

Pete
Hmm. I can't quite make out just what improvement (if any) that mod. is meant to achieve. It's only a minor - if puzzling - change; I'd put it back to original.

Having said that (since this subject has now arisen), on the more general issue of modifications, by-and-large I agree with MichaelR. However - and this is where I really stick my neck way above the parapet , my 'take' on this thorny issue of modifications is as follows.
If I can satisfy myself that there is a deficiency in the original design and that it is relatively simple to fit a re-work which, in return, substantially improves performance, operability, maintainability or reliability, and provided that it isn't severe - such as substantially re-working major features, e.g. cabinet design - then I'll do the mod. But I'll make sure that I have thoroughly tested the receiver first and afterwards to establish that the mod. is worthwhile; that no untoward & unwanted 'knock-on' effects have occurred, and most importantly of all, fully document the changes with all measurement data. Obviously, if the mod. is easily reversible, so much the better. If the receiver in question is one that I have no intention of disposing of, then the more likely I will consider the mod.

By way of illustration, examples that spring to mind are:
replacing a FW rect. valve with silicon diodes (heat reduction); relocating high-wattage resistors (that run hot) above the chassis (heat reduction); changing the values of capacitors in the BFO cct. to reduce the cap. swing (so as to make SSB resolution easier); increasing BFO injection on receivers that were originally primarily designed for CW reception (to improve reception on SSB); adding insulating material over high-voltage exposed points that I may contact during servicing (safety); fitment of bleeder resistors on HV PSU caps. (safety); replacing 2-core mains cable with 3-core (except for a.c. / d.c. sets - which I tend to avoid anyway).

Finally, the quality of the workmanship of the mod. must be at least up to the standard of the original set and, ideally, not look obvious - let alone unsightly!

Anyway, for what it's worth, that's my viewpoint on this delicate issue

Al. / Skywave.

Last edited by Skywave; 3rd Nov 2008 at 1:58 am. Reason: Spelling; grammar
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Old 3rd Nov 2008, 9:38 am   #26
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Exclamation Re: Eddystone 640

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Originally Posted by Skywave View Post
Apart from the usual replacement of old capacitors & high-value resistors, check that the metallizing on the EF39 IF amp. is intact - otherwise the IF amp. will go unstable.
Has anybody tried respraying these valves (or others with similar problems) with metallic zinc from the CRC "Zinc It" galvanising in a can range? The top rated product offers 95% pure zinc and it strikes me that percentage of zinc in the coating should provide a good screen. It is also available in red, blue, green, gold and some other colours (at lesser zinc content percentages) which could be good for authenticity.

It might be worth giving it a go, and I have an EF39 here that has lost enough shielding to become unstable so I may try it and see what happens.

Cheers

Billy
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Old 3rd Nov 2008, 10:20 am   #27
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Default Re: Eddystone 640

On the subject of mods I have no hesitation in doing them if I think it worthwhile. However all mods should be reversible, front panels should never be drilled and all mods should be documented for the next owner.
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Old 3rd Nov 2008, 10:23 am   #28
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Default Re: Eddystone 640

I will go as far as that as well Al...

Mike
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Old 3rd Nov 2008, 5:56 pm   #29
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Default Re: Eddystone 640

hi.

Well I've taken the mod out. Much the same really. No I do not like mods. I have though put in a fuse and put a 47k resistor across C72. I think I'll put in a double pole switch. Are they mods! or just being safe. I'll live with it...

But it must be said this set is really nice.

Pete
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Old 3rd Nov 2008, 11:33 pm   #30
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Thumbs up Re: Eddystone 640

Quote:
Originally Posted by Station X View Post
On the subject of mods I have no hesitation in doing them if I think it worthwhile. However all mods should be reversible, front panels should never be drilled and all mods should be documented for the next owner.
Agreed!

Al.
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Old 3rd Nov 2008, 11:52 pm   #31
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Thumbs up Re: Eddystone 640

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Has anybody tried respraying these valves (or others with similar problems) with metallic zinc in an aerosol can . . .
Billy
Yes, I have: it works well.

To preserve to earthing of the metallization, I give one coat, then wrap a half-inch wide strip of self-adhesive copper tape, evenly spaced, where the bakelite base meets the envelope, wrap a 22 swg wire around the valve - and on top of the tape - where the glass enters the bakelite base. Next, solder this wire to the conductive tape all the way round & solder the other end of the wire to pin 1 (Octal valves) on the outside on the bakelite base. Then a final coat. I use masking tape on the base and top cap area. A new legend (e.g. "EF39") is then carefully applied to the paint when dry.

With care & experience, you can end up with quite a presentable 'valve repair'

Aside: for clarity, slight adjustment to the Quote made by Skywave.

Al / Skywave.
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Old 3rd Nov 2008, 11:59 pm   #32
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Default Re: Eddystone 640

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Originally Posted by peter.sables View Post
hi.

Well I've taken the mod out. Much the same really. No I do not like mods. I have though put in a fuse and put a 47k resistor across C72. I think I'll put in a double pole switch. Are they mods! or just being safe. I'll live with it...
Pete
Strictly speaking, yes, they are modifications. OTOH, it could be argued that you've corrected design short-comings / over-sights by doing those things. The S640 - like most radios - was built to a specification and a price. Moreover, even manufacturers occasionally call for post-sales retrofits to be installed on occasions.

Al.
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Old 4th Nov 2008, 10:25 am   #33
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Default Re: Eddystone 640

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Originally Posted by Skywave View Post
Yes, I have: it works well. Al / Skywave.
Excellent, it is always good to know that the ground has been well trodden and the thorns removed before you venture down strange pathways.

Cheers

Billy
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Old 4th Nov 2008, 1:28 pm   #34
peter.sables
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Default Re: Eddystone 640

hi ALL

Thanks for your excellent help in this project. The project is now complete and up and running...

Pete
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