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Old 22nd Apr 2021, 2:30 pm   #1
BrianAllen
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Default HMV 1120 Very Strange Goings On

I have an HMV 1120 that has been recapped and had replacement valves (mostly sourced here) as all valves were all missing.

Whilst I know there could be a 101 reasons for the following any input would be good.

Put quite simply whilst operating the set horizontally, if I gently tap anywhere on the chassis or components (very lightly that is) there is loud interference but stand vertically on end and no interference whatsoever, no matter how hard I tap the chassis, whether with a finger or rubber end of a pencil.

Any suggestions as to what may be causing the interference are most welcome.

Brian
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Old 22nd Apr 2021, 3:00 pm   #2
BrianAllen
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Default Re: HMV 1120 Very Strange Goings On

Here is a quick update.

If I lower the chassis from vertical to horizontal the interference starts.
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Old 22nd Apr 2021, 3:10 pm   #3
Station X
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Default Re: HMV 1120 Very Strange Goings On

Often caused by loose cores in IF Transformers. Sometimes sets suffering from this will only operate upside down rather than the right way up, or vice versa.
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Old 22nd Apr 2021, 3:15 pm   #4
cathoderay57
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Default Re: HMV 1120 Very Strange Goings On

What does the interference sound like? If it is a ringing sound you could have a microphonic valve. Jerry
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Old 22nd Apr 2021, 3:37 pm   #5
BrianAllen
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Default Re: HMV 1120 Very Strange Goings On

No, it's just lot of interference which sounds like connecting a battery to the speaker terminals and rubbing the wire over one of the terminals (the volume control has no effect over the loudness of interference.

It's almost as if there were a ball bearing in a tube and just as the set gets to horizontal the interference starts.

Luckily, I do have another set, so will take a closer look at that one and compare as not yet had a good look at this other set.

Brian
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Old 22nd Apr 2021, 3:41 pm   #6
60 oldjohn
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Default Re: HMV 1120 Very Strange Goings On

I had a Bush DAC90 on the bench 2 weeks ago. Thought I had a noisy valve, tapping the end of the case made it worse, also tapping the chassis sounded worse. Lightly tapping each valve made no difference. Reached across my bench to switch off the phone charger made it very noisy. Once charger was switched off no amount of tapping would make the noise. I put it down to being hand capacitance with me picking up noise from the charger.

John.
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Old 22nd Apr 2021, 3:45 pm   #7
cathoderay57
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Default Re: HMV 1120 Very Strange Goings On

With the noise present switch to gram and see if the noise stops. If it does you know the noise is coming from V1 or V2 stage. If it doesn't then try grounding the grid1 of V4 the output valve. If the noise doesn't stop then the fault lies in the V4 stage. If it does stop then the noise is coming from V3. Cheers, Jerry
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Old 22nd Apr 2021, 4:22 pm   #8
BrianAllen
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Default Re: HMV 1120 Very Strange Goings On

Hold fire gents.

After your posts, I got the set out again and would you believe, it's not now doing it; been running for about 20 minutes now but should it start again I will revert to your advice.

Just a thought, could it be that these old radios can take a little time to settle in if not been used for 20, 30, 40 years and having replacement caps/components?

Brian
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Old 22nd Apr 2021, 4:43 pm   #9
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Default Re: HMV 1120 Very Strange Goings On

Could there have been a bit of conductive grit in the variable capacitor vanes, and changing from horizontal to vertical distorted the chassis or VC sufficiently to just break contact, and it's now fallen out (or moved just enough to make the problem happen tomorrow or in a year's time....). The joy of trying to keep things going decades longer than originally intended
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Old 22nd Apr 2021, 5:00 pm   #10
BrianAllen
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Default Re: HMV 1120 Very Strange Goings On

I wonder if it started to work as intended because it gave me a "belt" (nothing too bad and first one since I started working on radios a year ago) no I didn't have one hand behind my back but I will in future. Obviously just a coincidence but giving me a warning to take care!!
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Old 22nd Apr 2021, 7:55 pm   #11
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Default Re: HMV 1120 Very Strange Goings On

My best guess is you have, or had, a dirty valve pin or pin socket somewhere. Turning the set on its side could have altered the weight distribution and induced/removed the fault. If it comes back then give the valve sockets a good squirt of Deoxit or similar switch cleaner. Ditto wavechange switch contacts. Cheers, Jerry
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