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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 3rd Dec 2011, 8:50 pm   #21
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Default Re: 'Underwater' sound from valved amp.

Do you have a source of audio other than from the Juke Box's deck? An MP3 player maybe? Connecting this to the input of the amp with the deck unpowered and disconnected from the cartridge would eliminate any deck problems.
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Old 3rd Dec 2011, 11:12 pm   #22
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Default Re: 'Underwater' sound from valved amp.

Quote:
Originally Posted by Station X View Post
Do you have a source of audio other than from the Juke Box's deck? An MP3 player maybe? Connecting this to the input of the amp with the deck unpowered and disconnected from the cartridge would eliminate any deck problems.
My first thought was of a deck problem causing a vibrato effect - known as 'wow' on tape decks
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Old 3rd Dec 2011, 11:18 pm   #23
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Default Re: 'Underwater' sound from valved amp.

or flutter
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Old 3rd Dec 2011, 11:28 pm   #24
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Default Re: 'Underwater' sound from valved amp.

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Originally Posted by pwdrive View Post
or flutter
Quite so
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Old 4th Dec 2011, 9:44 am   #25
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Default Re: 'Underwater' sound from valved amp.

Looking at the diagram which is on pages 30/31 of Nicks service manual, nd reading his posts about the fault. It would appear that either the source is causing the problem or the first stage which is centred around the C6G7 valve.

The only components common to BOTH channels is the cathode resistor and its decoupling capacitor the resistor is 1K and the capacitor 100uF.

I suggest you check these components, preferably by substitution.

Unfortunately the diagram doesn't give component reference numbers and the diagram isn't particularly easy to read but if you look closely, the resistor is connected to pin 8 and ground, the capacitor between pin 3 and ground and that pin 8 is connected to pin 3 thus paralleling these components.
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Old 4th Dec 2011, 11:33 am   #26
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Default Re: 'Underwater' sound from valved amp.

Thanks Michael, I will pay that area attention as well as change that resistor as a matter of course along with the capacitors (which are all 50 years old). As far as the source, All is ok with a fairly new sc12M cartridge fitted.tracks ok into the amp but will double check.
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Old 5th Dec 2011, 7:47 am   #27
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Default Re: 'Underwater' sound from valved amp.

Possibly daft question: Are you sure it's meant to be fed from a ceramic cartridge? Seeburgs and later Rock-Olas used magnetic carts.
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Old 5th Dec 2011, 8:10 am   #28
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Default Re: 'Underwater' sound from valved amp.

Hello
Forgive me for butting in I don’t consider myself an expert but I have been following this thread. Is it possible for the tracking to be out or stiff on the record arm. Many records are not always centred on the platter and you often see the arm moving to and fro as the record plays. This could result in a pulsing effect on the audio and this would change with the speed of the rotation of the record. (I guess the speed of a juke box is set at 45 rpm unless it can play LP's)
If the “underwater” effect is not present when an external source is used then this would surely point to the cartridge/deck mechanism not the amp circuit.
Mike
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Old 5th Dec 2011, 8:22 am   #29
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Default Re: 'Underwater' sound from valved amp.

This is the 29th post in this thread. We still don't know what "underwater sound" is. There has been speculation that it could be mains hum, wow, flutter or something else. We still don't know whether the problem is with the deck/cartridge or the amplifier. Unless we get more information we can only speculate as to what the fault is and how to cure it.

Quote:
All is ok with a fairly new sc12M cartridge fitted.tracks ok into the amp
What exactly does "tracks OK into the amp mean"? A track on the record? The tracking of the arm/cartridge? Tracks on a PCB? Whether or not a deck tracks correctly, it's immaterial as to whether it's connected to an amp or not. A deck doesn't need to be connected to an amp in order to check the tracking. How do you know it "tracks OK into the amp"?
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Old 5th Dec 2011, 10:59 am   #30
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Default Re: 'Underwater' sound from valved amp.

Hello Graham,

That's why a recording of the effect would be invaluable!

Regards,

Dave.
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Old 5th Dec 2011, 11:02 am   #31
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Default Re: 'Underwater' sound from valved amp.

Quote:
Originally Posted by musonick
Hi, it's probably too subtle to do a recording but it's 'there'. It's the actual audio signal fluctuating.
I'd have thought that if you can hear it you can record it.

Fluctuating in pitch, amplitude or both? What's the frequency of fluctuation?
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Old 28th Feb 2012, 9:05 am   #32
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Default Re: 'Underwater' sound from valved amp.

Sorry for the late resolution to this thread but i have been in the subcontinent for some time. Pleased to say the fault has been traced.
It is a machine that we only get to visit once in a while hence the difficulty obtaining recordings etc.
Thank you all and particularly Crackle who provided the clue. cable grommets had been fitted to the TT motor instead of the correct ones hence the idler was not riding correctly. The fault really did sound like an amp fault rather than mechanical, something i shall not overlook in future!
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