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Old 29th May 2019, 4:57 pm   #1
roberthewitt
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Default Racal RA17 Noisy Film Dial

Hi all

My RA17 works well but the kHz film dial is quite noisy (best described as crackling noise) as it rotates around both spigots.

I have tried various tension adjustments of the film but it doesn't seem to help much. Not having used an alternative RA17, I am not sure if this noise is excessive or normal?

The noise is eminating from the cog as it engages the film dial.

Just wondered if anyone can suggest a means of eliminating or reducing the noise?

Thanks in advance.

Also its starting to hum a bit!!

Robert
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Old 29th May 2019, 11:21 pm   #2
Colinaps
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Default Re: Racal RA17 Noisy Film Dial

Quote:
My RA17 works well but the KHz Film dial is quite noisy (best discribed as crackling noise) as it rotates around both spigots .
Sprockets? Has it been damp? Maybe a tiny dose of some sort of silicone polish like ArmorAll on the sprockets would help but please don't blame me if your filmstrip dissolves!

Quote:
Also its starting to hum a bit!!
Assuming you don't mean it contains a decomposing mouse dynasty , it's probably drawing lots of HT current due to leaky decoupling capacitors. If they're really bad there will be wax puddles underneath them and they will have gone from their original silver, through various shades of yellow and brown, ultimately to black and wrinkly.
A stock of mylar, aka PETP, 0.1uF, 150V or better and 0.01uF at 300V or better is a must for keeping an RA17 healthy. You'll be able to get both with 400V rating in a smaller package than the original. The nice yellow Vishay ones are good - I bought a stock of Russian military "surplus" PETP caps a few years back but the prices have gone up a bit since.

It may also be the big electrolytic in the PSU but I haven't had any trouble with them over 20-odd sets. Another possibility one half of the rectifier starting to fail but the wax/paper caps are more likely.

73

Colin.
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Old 30th May 2019, 12:36 pm   #3
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Default Re: Racal RA17 Noisy Film Dial

It's possible it's just that the rollers have seized.
Rob Filby, of the Racal RA17 forum, had some of the original smoothing caps for these. Sorry I don't have contact details to hand
Don
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Old 30th May 2019, 3:13 pm   #4
roberthewitt
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Default Re: Racal RA17 Noisy Film Dial

Thank you for suggestions.

I am reluctant to put anything on the film for obvious reasons. The film kind of clicks as the square holes dislodge from the spigot as the dial is turned which is why I thought maybe the tension on the 2 bobbins wasn't correct but having adjusted the tension it is still quite noisy. The rollers are fine otherwise. Maybe the film is becoming less flexible with age? I need to listen to another RA17 to see how mine compares noise wise!

It is annoying for an otherwise fine receiver.
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Old 31st May 2019, 12:25 pm   #5
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Default Re: Racal RA17 Noisy Film Dial

Hi,
It sounds to me as though the spacing between the rollers is not correct. The spikes on the rollers are there to index the film scale, not to pull it round. So, at rest, the spikes should be in the middle of the index holes in the scale and so should not touch the scale as it leaves the drum. Movement of the scale is achieved by rotation of the drum, with the scale held in tension by the drum springs.
Unfortunately I do not have a receiver in front of me to see how the spacing adjustment on the drums is achieved, but from memory there is a slotted securing screw on the take-up drum. Apologies if this is not correct.
Good Luck.
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Old 31st May 2019, 5:33 pm   #6
roberthewitt
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Default Re: Racal RA17 Noisy Film Dial

Thanks Peter
You could be right ..I will investigate to see if I can adjust the spacing.I readjusted the tension and it helped but did not solve the problem

Robert M0HFN
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Old 31st May 2019, 6:12 pm   #7
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Smile Re: Racal RA17 Noisy Film Dial

I have one though not to hand at present.
Could it be that if both the spigot rollers are driven together by the tuning knob shaft maybe that they are misaligned by the gearing to the tuning knob by a tooth or 2 to cause sprocket hole misalignment. I presume the tuning mechanism hasn't in the past been dismantled and reassembled? How is the calibration?

Christopher Capener
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Old 31st May 2019, 10:11 pm   #8
emeritus
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Default Re: Racal RA17 Noisy Film Dial

Some types of plastic film used in the 1950's do shrink with age. No experience with this radio, but I have noticed that the plastic sheet used for the windows of 1950's Hornby Dublo suburban coaches has shrunk significantly on all the examples I have come across, despite being firmly sandwiched between two sheets of tinplate, so the the edge of the sheet becomes visible at the side of one or both end windows.
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Old 2nd Jun 2019, 10:17 pm   #9
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Default Re: Racal RA17 Noisy Film Dial

My Racal makes a whirring sound when tuned, but its not at all a bother.
I have no idea what's wrong with yours, but it it bothers you, something is wrong.
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Old 5th Jun 2019, 3:18 pm   #10
roberthewitt
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Default Re: Racal RA17 Noisy Film Dial

Thank you all for your input. I have re adjusted the tension in the film sprockets making them quite tight (certainly more than the 3/4 turn recommended) and while it hasn't completely eliminated the noise it is now bearable so I will leave it at that and put the front panel back on !

Unfortunately another problem has emerged where the receiver is working fine for 10 -20 mins then goes quiet. If turned off for a while and then turned back on it does the same thing . Presumably valve or component over heating ?
I plan on injecting a signal at various stages to see if I can narrow it down to a specific area

Robert MOHFN
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Old 5th Jun 2019, 6:54 pm   #11
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Default Re: Racal RA17 Noisy Film Dial

You can always use a bit of "freezer" on the components,though not on the valves.Try to isolate which stage.

By quiet I presume lack of signals not low audio?
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Old 5th Jun 2019, 6:58 pm   #12
dtvmcdonald
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Default Re: Racal RA17 Noisy Film Dial

Quote:
Originally Posted by roberthewitt View Post
Thank you all for your input. ...

Unfortunately another problem has emerged where the receiver is working fine for 10 -20 mins then goes quiet. If turned off for a while and then turned back on it does the same thing .
Robert MOHFN
Welcome to the club. Mine had several such episodes, each being a bad
resistor (when hot only) or one of those bad red mica caps.
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Old 5th Jun 2019, 7:32 pm   #13
roberthewitt
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Default Re: Racal RA17 Noisy Film Dial

Quote:
Originally Posted by HamishBoxer View Post
By quiet I presume lack of signals not low audio?
Yes lack of signal , audio still present.

What type of freezer please .. Airosol spray ??
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Old 6th Jun 2019, 11:56 am   #14
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Default Re: Racal RA17 Noisy Film Dial

Sorry,yes aerosol from most places,RS or CPC etc. Always used to help me find heat related faults on tv,s.
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Old 7th Jun 2019, 10:48 am   #15
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Default Re: Racal RA17 Noisy Film Dial

Monitoring the AGC voltage may help to narrow it down to either the RF or AF stages.
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Old 7th Jun 2019, 12:01 pm   #16
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Default Re: Racal RA17 Noisy Film Dial

Hi,
You could try disconnecting the 250v link on the rear panel to kill the front end and injecting a signal (or attach an antenna) to the 2-3Mc/s input (PL3) on the rear panel and tune the kc/s dial to receive a signal. This will tell you if the problem is front end or back end.
Good luck
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Old 7th Jun 2019, 5:08 pm   #17
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Default Re: Racal RA17 Noisy Film Dial

Poundland air duster (for a pound) used upside down makes a great freezer spray.
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Old 7th Jun 2019, 9:18 pm   #18
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Default Re: Racal RA17 Noisy Film Dial

Very clever sir; take a bow!
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Old 12th Jun 2019, 7:21 am   #19
roberthewitt
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Default Re: Racal RA17 Noisy Film Dial

Thank you for that suggestion .. off to pound shop today !
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