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Old 21st Feb 2017, 11:46 am   #1
vampyretim
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Default Dynatron SRX 20 Speakers

Hi,

I'm repairing a Dynatron SRX 20.

I've managed to track down and install a CA3094A op amp and now got the thing working, however one of the bass speakers has come off centre and I will need to find a replacement.

I'm measuring about 12 ohms D.C resistance. It measures 8 by 5".

Does anyone know where I could get a replacement from?

Has anyone got anything suitable lying around?

Many thanks,
Tim.
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Old 21st Feb 2017, 12:03 pm   #2
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Default Re: Dynatron SRX 20 Speakers

I might have one - could you post a pic so I can check?

Roger
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Old 21st Feb 2017, 2:20 pm   #3
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Default Re: Dynatron SRX 20 Speakers

Hello Roger,

Thanks for the reply, please see photo.

Thanks again,
Tim.
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Old 21st Feb 2017, 2:39 pm   #4
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Default Re: Dynatron SRX 20 Speakers

These were originally Goodmans units and as you can see have a treated cone. There will be lots of 8" x 5" @ 3 ohms around I'm sure, but the 12 ohms impedance are not such an easy find. The right sized Car Audio speaker will only 4 ohm.
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Old 21st Feb 2017, 2:59 pm   #5
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Default Re: Dynatron SRX 20 Speakers

Hello Tim - I have a couple of spare 8 X 5s - one is a Fane, the other doesn't admit to being made by anyone but it works and looks OK - you are welcome to either. Just spotted you are in Bristol - whereabouts?

Cheers Roger
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Old 21st Feb 2017, 3:07 pm   #6
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Default Re: Dynatron SRX 20 Speakers

You'll need to check the impedance of those speakers, Roger, and the 'OP' needs to re-check the impedance of the one he's got to make sure he's got it right.
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Old 21st Feb 2017, 3:28 pm   #7
Edward Huggins
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Default Re: Dynatron SRX 20 Speakers

The Fane speaker is likely to be 3 ohms and the other, which lookes like a Grundig, is likely to be 5 ohms.
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Old 21st Feb 2017, 5:04 pm   #8
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Default Re: Dynatron SRX 20 Speakers

Quote:
Originally Posted by Techman View Post
You'll need to check the impedance of those speakers, Roger, and the 'OP' needs to re-check the impedance of the one he's got to make sure he's got it right.
So I should! They both measure just under 7 ohms. I can spare a pair of either if that helps.
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Old 21st Feb 2017, 5:16 pm   #9
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Default Re: Dynatron SRX 20 Speakers

Hi guys,

thanks for replying.

I'm measuring 14 ohms on both my AVO and dmm so I guess I'm a bit stuck!

Thanks all the same Roger.

Thanks again guys,
Tim.
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Old 21st Feb 2017, 5:34 pm   #10
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Default Re: Dynatron SRX 20 Speakers

I thought so! Yours is a 15 ohm and Rogers are 8 ohm.

Why don't you have a go at fixing yours and keep things original?

Many forum members have fixed off centre speakers and if you have a look, there's quite a bit of information on doing it in past threads.

Mounting the speaker upside down in the cabinet can sometimes make it 'sag' the other way and cure the problem - I did this with a speaker in an old tape recorder the other day!
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Old 21st Feb 2017, 6:19 pm   #11
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Default Re: Dynatron SRX 20 Speakers

Has the cone rear suspension become unstuck? It's uncomon for this sort of small speaker to go out-of-centre without some sort of damage.
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Old 21st Feb 2017, 6:57 pm   #12
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Default Re: Dynatron SRX 20 Speakers

Hi guys,

Thanks for all your help.

It's funny but I have repaired a lot of speakers lately.

I've replaced foam surrounds and repaired cone rear suspension.

I didn't realise you could recentre a cone. The rear suspension in this case is fine but I have never seen a speaker come this far off centre and turning it upside down won't fix something this far gone.

The cone is badly rubbing so much so that the cone gets stuck.

I would be up for giving this a go.

Anyone got any advice?
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Old 21st Feb 2017, 7:01 pm   #13
Edward Huggins
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Default Re: Dynatron SRX 20 Speakers

These are downward firing Bass/Midrange only units, mounted undeneath the Radiogram with seperate mid range/tweeters to each side. A replacement bass/mid range unit will need to have a good cone excursion to match the original sound of the Dynatron.
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Old 21st Feb 2017, 10:57 pm   #14
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Default Re: Dynatron SRX 20 Speakers

Use a scalpel to remove the central dust cover from the cone, then you can use shims of, say, card to centre the voicecoil. It's unclear what's moved here though - it looks like a glued magnet, which wouldn't move without falling off altogether. Has the cone got damp, perhaps? It looks in good nick.
Otherwise, there might be something in the airgap, metal filings for instance.
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Old 22nd Feb 2017, 10:08 pm   #15
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Default Re: Dynatron SRX 20 Speakers

Hi guys,


I cut off the dust cover today and had a look but couldn't really see the cone rubbing. I'm quite confused as the speaker seems to be freer to move now that I've been manually compressing the cone.

I don't really get what's going on but I'm going to put the speaker back in tomorrow and see how it is now.

It's not getting stuck like it was.

I'll report back tomorrow.
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Old 23rd Feb 2017, 12:14 am   #16
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Default Re: Dynatron SRX 20 Speakers

If it does face down, perhaps something was lodged in it and has now cleared unnoticed?
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