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Old 27th Nov 2015, 1:39 am   #41
Skywave
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Arrow Re: Eddystone 888A.

Quote:
Originally Posted by carnivalpete View Post
I couldn't find a way to solder the stuff (tuning drive wire) as Eddystone had done.
The clue is to get the wire really bright and shiny clean. Then use a really hot iron (such as a 'Metcal') and an additional flux paste, such as 'Coraline' - which for solder-resistant joints, I wouldn't be without: it's superb stuff - and it's non-corrosive.

Al.
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Old 27th Nov 2015, 7:03 pm   #42
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Default Re: Eddystone 888A.

Well Tanuki. The case has been painted and I can collect Saturday, the sticking point at the moment is the "goodness" of the valves. My valve tester says the EF91/6BA6 are low emission, but I don't believe it. I will post some photo's of progress in the next few days.
Skywave. All received and understood. The Eddy 888 only uses the dial drive cord just for that purpose, from two threaded drums driven from the gear assy.
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Old 29th Nov 2015, 7:00 pm   #43
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Default Re: Eddystone 888A.

Hi Peeps. Case collected Saturday, and front re assembled. Needed a few adjustments to the dial drive and flywheel drum. Fitted a single hole wire connector to the dial pointer to clamp the drive wire. Made new dial wire drum mounting posts.
The hard part was re assembling the front to the receiver chassis, you need fingers all over the place to get all to switches and pots into position.
Electrically needs some TLC, deaf as a post. Still past halfway.
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Old 30th Nov 2015, 8:18 pm   #44
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Default Re: Eddystone 888A.

Looks great, that'll be something to cherish. I do prefer this "'fifties" front panel casting to the earlier "'forties" half-moon and later "'sixties" functional but bland Eddystone panels.
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Old 30th Nov 2015, 9:09 pm   #45
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Default Re: Eddystone 888A.

Yes Turretslug. Much better castings, and the paint job was "crackle" finish too.
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Old 1st Dec 2015, 11:34 am   #46
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Default Re: Eddystone 888A.

That's looking nice!.. Like Turretslug I too prefer the 'finned' diecast front panel and full-size scale school of Eddystone styling.

One thing I never have managed to get my head round though is the way Eddystone *always* seemed to end up with one control-knob which incongruously didn't match the rest (the selectivity control on Wendymott's 888A, the noise-limiter switch on my 840A).
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Old 1st Dec 2015, 11:53 am   #47
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Arrow Re: Eddystone 888A.

The other 'feature' that I've always been perplexed about with the 888 / 888A is the aerial trimmer: fitted inside the cabinet, necessitating the opening of the hinged lid in order to adjust it. Now the designer must have been aware that with a 'longwire' type of aerial - which has been catered for on these sets - that trimmer would require re-adjustment from band to band. In my case, it is not a problem, since I use such an aerial with an external AMU / ATU - and always have done - rendering that control redundant.

The only conclusion I can come to is that the need for that trimmer was a late afterthought - but I quite prepared to listen to more acceptable theories.

Another puzzlement is the location of the headphone socket: fitted in the side of the cabinet: not exactly a convenient location.

Al.
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Old 1st Dec 2015, 8:53 pm   #48
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Default Re: Eddystone 888A.

Hi Wendy,

Looks great - much prefer the chunky casting to the "plasticy" smooth finish on the later Eddystones. I use a 680X regularly and find it ideal for the lower bands but a bit cramped at the top end. A nice feature is that you can switch in the crystal filter at any selectivity position - useful for nulling out unwanted carriers.

One question - what's this Osc Hi/Low malarkey? Calibration tweak perhaps?
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Old 1st Dec 2015, 9:08 pm   #49
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Default Re: Eddystone 888A.

The "Osc high/low" is used in association with the xtal calibrator to calibrate the dial.

Let's say you want to listen to a transmission on 3.615MHz; you first tune the radio's main dial to 3.600 then press the xtal-cal button and tweak the "Osc High/Low" knob to get zero-beat with the harmonic from the 100KHz crystal-derived calibration signal. This establishes a known high-accuracy mark at 3.600MHz on the main dial.

Then you tune 15KHz up on the main dial, and you're exactly on the frequency you wanted. This was the best you could do before the days of xtal-locked synthesizers, PLLs and frequency-counters.

Essentially the radio is self-calibrating because it has a built-in frequency-meter (so no need for the old Class-D Wavemeter or BC221 that was otherwise de-rigeur in amateur shacks of the 1950s).
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Old 2nd Dec 2015, 12:39 am   #50
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Default Re: Eddystone 888A.

Hi Peeps. Thanks for the comments. Yes I agree Tanuki ref the "odd" control knob, it is the same on my 750. The headphone socket on mine is bottom left front. and what a PAIN, it's location is too close to the Mains on off switch. I had fitted a Double pole switch with as narrow body as I could find. It looked ok until I came to fit the headphone socket. had to refit the single pole switch. grrrrr. Yes Skywave, whats the Aerial trimmer doing inside ?, as you say, an after thought.
I have just finished replacing the de coupling caps and carbon resistors, although in this receiver most were just out of value. However as they are carbon construction they were replaced with metal film, to hopefully reduce noise.
I also replaced the 5Z4 rectifier with silicon diodes in an Octal base, with series resistors to reduce the eventual voltage to 275, its highest voltage without the resistors was 300V, until conduction of the valves occurs, then it dropped to 290V DC. however it occurs to me that the heat generated by the 5Z4, may be similar or less than the power lost in the series resistors. I know that the 5Z4 will loose emission in time, but its not as though the receiver will be used often.
Alignment next.
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Last edited by Wendymott; 2nd Dec 2015 at 12:45 am. Reason: Additional data
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Old 2nd Dec 2015, 11:46 am   #51
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Default Re: Eddystone 888A.

From time to time I've heard a number of people discussing changing the 5Z4 for diodes. Not sure I understand it. Of course I understand the 5Z4 gets hot, but Eddystone knew that too. The radio was designed and tested with that level of heating. For what it's worth my first Eddy 888A managed regular use for 25yrs without any trouble and was still going well with the same valve set when I sold it on.
By the way, your triple eight is looking very good, and quickly too - I admire your work rate.
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Old 2nd Dec 2015, 12:09 pm   #52
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Default Re: Eddystone 888A.

The receiver does get hot though- and displacing the 5Z4 for silicon diodes is an easy 10W saving, which is a fair amount in anyone's book. I haven't siliconised my 750, but I did remove the original (and rather nice-looking) Brimar 5Z4G with its bulbous envelope and replace it with a metal 5Z4 with its much smaller envelope- the heater dissipation is precisely the same but the airflow is much improved around transformer, rectifier and VR150 in this cramped corner, making for a much less marked hot-spot at this rear corner of the case.

PS 'Cos I'm a safety weenie, I made sure to connect pin 1 of the rectifier socket to chassis when substituting the steel envelope valve.
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Old 2nd Dec 2015, 3:47 pm   #53
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Default Re: Eddystone 888A.

Quote:
Originally Posted by Wendymott View Post
Hi Peeps. Thanks for the comments. Yes I agree Tanuki ref the "odd" control knob, it is the same on my 750. The headphone socket on mine is bottom left front. and what a PAIN, it's location is too close to the Mains on off switch. I had fitted a Double pole switch with as narrow body as I could find. It looked ok until I came to fit the headphone socket. had to refit the single pole switch. grrrrr. Yes Skywave, whats the Aerial trimmer doing inside ?, as you say, an after thought.
Goes to show just how close together the controls are in the 888 models- in the 750 with two switches on each side, rather than three, there is room for a double-pole replacement of the same type. There seems to have been keen competition between comms receiver makers as to who could get the un-insulated mains switch tags closest to the un-insulated headphone socket tags- this challenge was subsequently eagerly joined by makers of hi-fi amplifiers/receivers.

I find the 750 chrome selectivity control quite ergonomic- with a hand over the main tuning, the pinkie (sorry, little finger) is nicely placed to tweak the selectivity- halfway clockwise for amateur bands, two-thirds round for broadcast segments. Nudge fully clockwise for congestion-free broadcast, fully anti-clock for CW.

That 888 and /A aerial trimmer control is clunkily placed- Eddystone seemed to have flair for precise mechanical detail, including co-axial controls in a number of sets, so it's a pity that the "Osc. Trim" didn't have a co-axial outer sleeve and "Ae. Trim" knob with short pulley drive to the trimmer in question. That would have been trick.
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Old 3rd Dec 2015, 11:19 am   #54
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Default Re: Eddystone 888A.

Hi Carnivalpete. Thanks for your comments. In the days of its manufacture there were no silicon diodes, only selenium, thus the 5Z4 was the best option. However the heat generated is quite high and all in that corner. I fitted an ex computer psu fan above this lot in my 750, which does help reduce frequency drift. The problem with replacing the 5Z4 with silicon is that the 1N4007 has a forward volts drop of 0.7V whereas the 5Z4 was approx. 20V. This extra voltage must be got rid of, thus 2 x 57 Ohm resistors are fitted, and they do get warm, but they do not include the heater of the 5Z4. I am also replacing the VR150 with a zener diode which will be attached to the chassis to spread the heat.
Regarding the time and effort. I like to get on with things. Being of the retired group, I have the time, being single I don't have too many distractions, and I do not like too many things on the "go" at once, thus I like to "clear the decks" before the next project.
Hi Turretslug. Its a shame the engineers at Eddystone didn't give me another 25 thou sideways, that would have been enough. I have sleeved the current switch so safety is maintained.
The latest problem, broken valve pin sockets. I noted when I was cleaning the valve pins that several sockets were a bit "Loose". On further investigation it seems the female pins have lost their springiness and at least 3 have broken. The RF valve socket was repaired with careful bending of the female half not broken and fitting the valve carefully. The BFO valve socket, had its two broken parts replaced, fortunately my spare sockets have the same construction, and I was able to replace the pins without replacing the whole socket.
I am getting the idea that the First oscillator which is a 6AM6 in mine, but triode connected, may, I say may be replaced with a high voltage FET, as its FT only need be say 50 Mhz, "I may be corrected on that", anyways I have ordered a couple to try.
Nothing ventured....
Onward and upward.
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Old 3rd Dec 2015, 10:13 pm   #55
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Default Re: Eddystone 888A.

Hi Wendy, as you have mentioned a "silicon" word, I suggest you look for Fetrons. There was a good article on them in a copy of WW in the 70's. This went over how they were being manufactured for use as valve replacements in communication receivers.

Ed
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Old 3rd Dec 2015, 10:34 pm   #56
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Default Re: Eddystone 888A.

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Originally Posted by Wendymott View Post
I am getting the idea that the First oscillator which is a 6AM6 in mine, but triode connected, may. I say may be replaced with a high voltage FET...... as its FT only need be say 50 Mhz, "I may be corrected on that", anyways I have ordered a couple to try...
Nothing ventured....
Onward and upward.
One of the various RSGB "Amateur Radio Techniques" books has a description of someone replacing the triode part of the ECH35 frequency-changer in an Eddystone 640 by a couple of 2N3819/MPF102-style FETs (powered from a voltage-doubler off the 6.3V heater supply) to reduce thermal frequency-drift.

There's a comment to the effect that the 2N3819 etc is "a humble 6C4-like device" - I'm sure that in the subsequent 40 years or so better FETs have emerged.
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Old 3rd Dec 2015, 11:25 pm   #57
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Default Re: Eddystone 888A.

Hi Tanuki..... Thanks for that......although... my thought was to do a "Direct" replacement without changing any components such as the Anode load.... the devices I ordered from CPC are out of stock... typical... but when they come I will try it and see what happens.... failing that, the suggestion of yours will be tried... Just replacing V6 valve base at present, cleaning and re tensioning did not work... hey ho.... fun starts here...
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Old 5th Dec 2015, 3:37 pm   #58
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Default Re: Eddystone 888A.

Hi Tanuki... Have you a "Soft" copy of the article re fets replacing 6C4 etc... or a quick hand drawn schematic please...
I have replaced V6 base with a ptfe type. Not as difficult as first thought...but V1, the RF amp in the diecast case is a bit more tricky.. in fact neigh impossible...will try and replace the broken pin only.
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Old 6th Dec 2015, 10:53 am   #59
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Default Re: Eddystone 888A.

I'll scan the relevant coupe of paragraphs and cct diagrams for you later today, OK??
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Old 6th Dec 2015, 8:48 pm   #60
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Default Re: Eddystone 888A.

Should be a couple of PDFs showing the "FET-isation" of an Eddystone 640 attached...
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File Type: pdf shrunk2.PDF (1.49 MB, 97 views)
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