Eddystone 680x - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

G6Tanuki · 13th Feb 2023, 6:34 pm

There's a very similar-looking little capacitor in my recently-acquired S.750; my instinct is to let it be, if only because, as others have mentioned, it may well come with circuit-considerations other than just pure capacitance.

Steve G4WCS · 14th Feb 2023, 6:01 pm

Been given some history of the radio by its previous owner, which would explain the bfo mod and bnc sockets having been fitted for the antenna connections.

On refection (some 30+ yrs ago) I didn't use it very much - it was about to be scrapped as redundant test gear and I put a bid in (£25 IIRC) as I didn't want to see a hammer through it! But life in those days was very much into PC's and so the 680 was eventually banished to the loft.

The probable reason for the bfo mods was that it was used (amongst other things) for testing FDM (Frequency Division Multiplex) line systems carrying analogue telephony channels (300 - 3.4 kHz) and each channel was ssb supressed carrier stacked 4kHz apart. The line systems had a range from 60 kHz up to several MHz, depending on the size (number of channels) of the line system.

Sophisticated test equipment was rare in the 50's and 60's and quite a number of engineers were Radio Amateurs, so hence the choice was for the 680 - which had an 'S' meter. They used a known signals thru' switchable attenuators to compare signal levels over the frequency spectrum of the line systems to confirm they were working correctly. So they could inject an audio tone (usually 800 Hz) onto any given channel and search for it on the line system and confirm its level (or absence, in the event of a fault).

Incidentally, the old CR100 preceded the S680X as test gear in the early 60's - just a very potted history!

Steve G4WCS · 14th Feb 2023, 10:18 pm

My leaky cap hunch was right. Replaced it and the set is alive

https://youtube.com/shorts/vIElDb0x9DM?feature=share

https://youtu.be/p6RxJ8KLxUg

https://youtube.com/shorts/YYHPC4R5Hy4?feature=share

turretslug · 15th Feb 2023, 12:08 am

Well spotted and a satisfying outcome- I take back my comment about their reliability! I suppose that with the passage of time, more and more component types hitherto regarded as trustworthy will inexorably succumb.

Steve G4WCS · 15th Feb 2023, 10:03 am

For clarification, I left the small cap in the vfo box. It was the 8uF electrolytic that I replaced.

Steve G4WCS · 16th Feb 2023, 7:40 pm

Boxed up a speaker

13th Feb 2023, 6:34 pm	#21
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Eddystone 680x There's a very similar-looking little capacitor in my recently-acquired S.750; my instinct is to let it be, if only because, as others have mentioned, it may well come with circuit-considerations other than just pure capacitance. __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

14th Feb 2023, 6:01 pm	#22
Steve G4WCS Heptode Join Date: Sep 2004 Location: Preston, Lancashire, UK. Posts: 632	Re: Eddystone 680x Been given some history of the radio by its previous owner, which would explain the bfo mod and bnc sockets having been fitted for the antenna connections. On refection (some 30+ yrs ago) I didn't use it very much - it was about to be scrapped as redundant test gear and I put a bid in (£25 IIRC) as I didn't want to see a hammer through it! But life in those days was very much into PC's and so the 680 was eventually banished to the loft. The probable reason for the bfo mods was that it was used (amongst other things) for testing FDM (Frequency Division Multiplex) line systems carrying analogue telephony channels (300 - 3.4 kHz) and each channel was ssb supressed carrier stacked 4kHz apart. The line systems had a range from 60 kHz up to several MHz, depending on the size (number of channels) of the line system. Sophisticated test equipment was rare in the 50's and 60's and quite a number of engineers were Radio Amateurs, so hence the choice was for the 680 - which had an 'S' meter. They used a known signals thru' switchable attenuators to compare signal levels over the frequency spectrum of the line systems to confirm they were working correctly. So they could inject an audio tone (usually 800 Hz) onto any given channel and search for it on the line system and confirm its level (or absence, in the event of a fault). Incidentally, the old CR100 preceded the S680X as test gear in the early 60's - just a very potted history!

14th Feb 2023, 10:18 pm	#23
Steve G4WCS Heptode Join Date: Sep 2004 Location: Preston, Lancashire, UK. Posts: 632	Re: Eddystone 680x My leaky cap hunch was right. Replaced it and the set is alive https://youtube.com/shorts/vIElDb0x9DM?feature=share https://youtu.be/p6RxJ8KLxUg https://youtube.com/shorts/YYHPC4R5Hy4?feature=share

15th Feb 2023, 12:08 am	#24
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: Eddystone 680x Well spotted and a satisfying outcome- I take back my comment about their reliability! I suppose that with the passage of time, more and more component types hitherto regarded as trustworthy will inexorably succumb.

15th Feb 2023, 10:03 am	#25
Steve G4WCS Heptode Join Date: Sep 2004 Location: Preston, Lancashire, UK. Posts: 632	Re: Eddystone 680x For clarification, I left the small cap in the vfo box. It was the 8uF electrolytic that I replaced.

16th Feb 2023, 7:40 pm	#26
Steve G4WCS Heptode Join Date: Sep 2004 Location: Preston, Lancashire, UK. Posts: 632	Re: Eddystone 680x Boxed up a speaker Attached Thumbnails