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Old 21st May 2020, 12:14 pm   #1
JoshWard
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Default Roberts R900 dial cord

Hi all,

The drive cord recently snapped on my shed/garden radio, a Roberts R900. I have found a diagram here: http://www.valve-radio.co.uk/literat...ervice-manual/

However, I am really struggling in getting it to work correctly! No matter what I do the cord ends up crossing over itself and jamming on the tuning spindle. I am not one hundred percent sure that I am following the diagram correctly. I am struggling to work out the orientation of the tuning gang drum on the diagram. The drum is at 90 degrees to the rest of the cord layout and when at maximum or minimum capacitance mine doesn't seem to end up pointing the same way as in the diagram!

Does anybody have any images of the cord route so I can try and work out what is happening here please?
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Old 22nd May 2020, 9:32 am   #2
simpsons
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Default Re: Roberts R900 dial cord

I have to agree that there has been some poetic licence in drawing the dial drive per the service manual. Given the size of the tuning capacitor drive pulley, I guess this caused some drafting issues.

Without taking my one apart, may I offer the following advice:

Cord the drive with the tuning capacitor in the Minimum capacity position, ie 200 metres/88 Mhz shown on the scale. It doesn't matter that the pulley isn't then looking exactly like the drawing. Remember, it did once work!

Make sure that you have cut the length of drive cord correctly, too tight and the drive will bind, too lose and the pulley spring will be slack. You can easily tie off a little extra cord on final assembly but you can't add to it

The diagram says 3 turns around the tuning knob spindle exiting as shown
and I see no reason why this isn't correct.

Patience my dear Watson, you'll get there in the end.

Chris
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Old 22nd May 2020, 7:56 pm   #3
jonnybear
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Default Re: Roberts R900 dial cord

The Tuning drum is at right angle to the drive cord, what are you using for the replacement cord?. I find using crocodile clips to hold cord in place helps, when you tie off the ends on the spring I always put a dab of nail varnish on the knot, there should always be tension on the spring so fit that last.
John
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Old 25th May 2020, 11:36 am   #4
JoshWard
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Default Re: Roberts R900 dial cord

Thanks for the advice. I am using a 0.6mm waxed linen cord which I have used on numerous other radios with no trouble. Maybe it's just a bit too wide for this Roberts?

I see that proper (thinner) dial cord is available on eBay so I'll order some of that and see if we have more luck.
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Old 25th May 2020, 12:16 pm   #5
Boulevardier
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Default Re: Roberts R900 dial cord

Quote:
Originally Posted by JoshWard View Post
Thanks for the advice. I am using a 0.6mm waxed linen cord which I have used on numerous other radios with no trouble. Maybe it's just a bit too wide for this Roberts?

I see that proper (thinner) dial cord is available on eBay so I'll order some of that and see if we have more luck.
Just in case this helps - I had a lot of problems using waxed cord on a 1970s Grundig portable. The cord ran through fine channels moulded into the plastic frame at the points where it had to turn through 90 degrees, and the narrowness of these channels shredded the wax off the line and into the channels where it seized up the whole drive action.
Also, the plastic cord (0.5mm fishing line) I used didn't grip at all well on the shiny plastic surfaces of the pulleys, and I had to rough-up the surfaces of line and pulleys with fine emery paper to get good grip. Whipping twine should also be OK, but don't use the waxed stuff if yours also has tight plastic channels like mine.

Mike
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Old 25th May 2020, 12:34 pm   #6
JoshWard
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Default Re: Roberts R900 dial cord

Thanks Mike. There are a couple of narrow pulleys on this one so perhaps that is the issue. Fingers crossed the new cord will sort it! I did once have a reel of original dial cord and have never found anything else which worked as well as that did! Sadly it was used up many moons ago.
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Old 26th May 2020, 9:12 am   #7
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Default Re: Roberts R900 dial cord

Hi Josh
What I have been using over the last 5 years is SS plastic covered very fine bowden cable works a treat,similar to the stuff that philips used, if you would like some PM me, if you want something thicker either carp line or badminton string, waxed cord tends to stick and gum up the drive.
John

Last edited by jonnybear; 26th May 2020 at 9:22 am.
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Old 28th May 2020, 11:16 am   #8
JoshWard
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Default Re: Roberts R900 dial cord

Thanks John, that's very kind of you. I'll see if the stuff I have ordered does the trick and if not I will be in touch
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Old 13th Jul 2020, 9:49 pm   #9
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Default Re: Roberts R900 dial cord

Well I finally got round to fitting the new dial cord a couple of weeks ago. This one was much thinner proper dial cord and it did the trick! Thanks for all the advice.
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