Eddystone Radio

[Murphyv310]

           
Hi.
I was given this Eddystone Radio today. It looks complete, a bit rusty and the dial cord is snapped. Not bad for nothing.
Any idea of the model? It uses Mullard octal valves.

[pwdrive]

According to what's on the control panel it's an s640.

Lawrence.

[Murphyv310]

Blimey strike me down with a feather Lawrence, I'm a blind old bat.
Thanks though

[Geordie McBoyne]

Hi Trevor,
I've two Eddystone radios. The sets are the later models and employ the Mullard U40 series valves.
I'd reckon your set with it's octal valves is the better set.

Geordie McBoyne.

[Synchrodyne]

The Eddystone 640 was more highly specified than the later 670 and 840 series.  The 640 was of the (1 x RF, 2 x IF) configuration, with a 1.6 MHz IF, whereas the 670 and 840 series were of the (1 x RF, 1 x IF) configuration, with a 450 kHz IF.  So with three-gang front ends throughout, the 640 would have had better image rejection at the higher HF frequencies.  Arguably the higher IF required the use of two IF stages to meet selectivity and possibly gain requirements, but even so, two stages at 1.6 MHz were probably better than one stage at 450 kHz.  The top-of-the-line (at the time) 680 model was of the (2 x RF, 2 x IF) type, with 450 kHz, this layout being common for higher performance communications receivers of the time.

Evidently with the 640 Eddystone obtained the desired AGC performance with agc bias applied to the RF, mixer and 1st IF stages, but not to the 2nd IF stage.  Having no (or at least significantly reduced) agc bias on the final IF stage was considered advantageous, and helped with the reduction of modulation rise distortion.

The 670 was designed as a marine cabin broadcast receiver, so was required to be able to operate on DC as well as AC supplies, down to 110 volts. Thus U-series valves were required.  Probably the voltage and cost constraints limited it to a (1 x RF, 1 x IF) configuration, although that was quite respectable by domestic receiver standards.  The 840 series was more-or-less a communications receiver version of the same concept.  A point of interest is that the final 670C and 840C variants, released in the early 1960s, retained the U-series Rimlock valves of the originals, probably long after Philips/Mullard had ceased offering them for new designs.

Strictly domestic receivers with serious shortwave broadcast reception intent seldom went past the (1 x RF, 1 X IF) layout.  For example, the Bush EBS44, Murphy TA160 and Pye PE80 were all of this type.  But the Ekco contender in this class, the A182, I think had two IF stages.  At the very upper end one found the (1 x RF, 2 x IF) format as for example in the Dynatron T69 and T99, Chapman S6BS and some of the Armstrong models.  Here there was more than enough gain for broadcast programme listening purposes.  As evidence, some of those, such as the Dynatron (from the T99A) and the Chapman S6BS (later variants at least) had preset IF gain controls that allowed the gain to be reduced where required.  Perhaps that’s why a 2nd RF stage was very rare in domestic receivers.  Where four gangs were used for better RF selectivity, as in the Dynatron T69D and T99, the fourth was used to form a bandpass, either input or interstage.  That also avoided undue narrowing of the RF passband.  On the other hand, for communications purposes, where reading of signals that were much weaker than the signals than were usable for entertainment purposes was required, and very narrow passbands were acceptable, the extra RF stage was advantageous.


Cheers,

Steve

[Murphyv310]

Thank you Steve for a very informative post.
I'll be dismantling the set in a week or two as in the meantime I've a 50's table top Ferguson radiogram to do. It has two EL84's in push pull and a good sized elliptical speaker. I'll post up pictures on a new thread soon.

[Murphyv310]

Hi.
Well I did some preliminary checks on the Eddystone today. I decided on a near to HKS approach as possible. The reason being the set has had work done in the past and I wanted as far as possible to see and hear what was good or bad. Most of the valves had lost their metalising to some extent so I had a look for some spares before I powered the set up. On closer inspection I found the crystal switch to be broken and most of the controls loose, I made sure there was no shorts and applied 120v from the variac for around 30 mins. The 6V6 was duff so that was the first to go. 150v and audio was strong from the 6Q7 top cap, no joy from the rf nor clicks from the first IF, another EF39 was fitted and at last some clicks from the bandwidth, at 210v there was noise but the IF was unstable. Signals could be heard so that's as far as I went. Big strip down tomorrow and the work commences. Pictures to follow.

[Murphyv310]

               

Tomorrow I'll take some more pictures when I start to dismantle the set.

[Murphyv310]

                           
Hi.
What an awful radio to repair, God help those engineers that had to do drive cords...... Well I have removed the front panel, itself a rubbish job to do, the glass and dial have to be removed and this has to be an after thought as are the controls and switches. Probably a job for those with long thin fingers but I'm disappointed in Eddystone and their lack of thought for repair.
Well I did the the three cords, some plonker in the past did away with the bandspread cord to the pointer and did it his own way which didn't work. This has now been sorted out.
The slide switch for the Xtal was broken and TBH due to lack of room I can understand. I've still the controls to sort out and refit the front panel, scale and glass which will no doubt fill the air with Billy Connelly expletives. I also have changed the 0.01uf caps in the RF and IF sections and checked the audio output stage and replaced two faulty components. I also have powered the set back up and have better results than yesterday, not brilliant but improved. Next will be to check the resistors for value and once done do a full realignment.  

[pwdrive]

The only Eddystone I owned was a 358x, give me an HRO anyday

Lawrence.