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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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1st Nov 2008, 1:28 am | #21 | |
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Re: Eddystone 640
Quote:
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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2nd Nov 2008, 8:04 pm | #22 |
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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 |
2nd Nov 2008, 9:06 pm | #23 |
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Re: Eddystone 640
HI.
This is just one mod. to my 640. What was on his mind and is it worth keeping!. Pete |
3rd Nov 2008, 12:38 am | #24 |
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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 |
3rd Nov 2008, 1:56 am | #25 | |
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Re: Eddystone 640
Quote:
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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3rd Nov 2008, 9:38 am | #26 | |
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Re: Eddystone 640
Quote:
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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3rd Nov 2008, 10:20 am | #27 |
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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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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
3rd Nov 2008, 10:23 am | #28 |
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Re: Eddystone 640
I will go as far as that as well Al...
Mike |
3rd Nov 2008, 5:56 pm | #29 |
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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 |
3rd Nov 2008, 11:33 pm | #30 |
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Re: Eddystone 640
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3rd Nov 2008, 11:52 pm | #31 | |
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Re: Eddystone 640
Quote:
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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3rd Nov 2008, 11:59 pm | #32 | |
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Re: Eddystone 640
Quote:
Al. |
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4th Nov 2008, 10:25 am | #33 |
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Re: Eddystone 640
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4th Nov 2008, 1:28 pm | #34 |
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Re: Eddystone 640
hi ALL
Thanks for your excellent help in this project. The project is now complete and up and running... Pete |