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Old 18th Sep 2008, 9:56 am   #1
Hunts smoothing bomb
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Default Advice needed with Philips B6X12A

Hi all,

I have the above set, (I think the model No. is right)

It is a stereo set (on gram input anyway) The set uses 800ohm speakers! The output valves are 2 EL84's (one per channel)

The problem is that one of the speakers is U/S, the voice coil is grating on the magnet and there is no adjustment that I can see, I no it wont be original but can I simply replace the output transformers so that coventional low impedance speakers can be used?

Many thanks
Lee
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Old 18th Sep 2008, 10:12 am   #2
peter_sol
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Default Re: Advice needed with Philips B6X12A

Are You sure it uses output transformers, as usually the high impedance speaker is used to avoid the need for them.
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Old 18th Sep 2008, 10:28 am   #3
Kat Manton
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Default Re: Advice needed with Philips B6X12A

Hi Lee,

Since the schematic isn't available from Paul Stenning, here's a link to one, (320k .pdf)

It does use transformers but the primaries are tapped, so replacing them is not necessarily quite as straightforward as it could be.

One thought crossed my mind, it'd be possible to wind a couple of autotransformers to match low-impedance speakers to the set. That'd leave the output stage circuitry undisturbed making it easier to return the set to original should a replacement high-impedance speaker be found at a later date.

Cheers, Kat
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Old 18th Sep 2008, 11:52 am   #4
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Default Re: Advice needed with Philips B6X12A

This sounds like a variant of the 'Reverbeo'. I restored a similar set of the 'bi-ampli' type that used small output transformers with 800 ohm speakers. Before you condemn the speaker, check that the corrugated suspension disk (that attaches to the cone) hasn't come adrift. If it has, you can use something like Evo-Stik sparingly to glue it back into place. I've done this a number of times with good results.


Rich.
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Old 18th Sep 2008, 1:30 pm   #5
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Default Re: Advice needed with Philips B6X12A

Hi All,
Thanks for the replies, Rich I have had the set completely to bits and the speakers were taken out. They are in very good condition and it is definitely the voice coil scraping on the magnet.

Kat, I like your idea would that be just a small number of turns of wire around the core?
How many?

I'm posting a request for a replacement speaker in the relevant section.

Cheers
Lee
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Old 18th Sep 2008, 1:42 pm   #6
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Default Re: Advice needed with Philips B6X12A

Hi Lee,

Try twisting the speaker frame gently with your hands, whilst playing, and see if you can get any improvement.

David
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Old 18th Sep 2008, 3:55 pm   #7
Kat Manton
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Default Re: Advice needed with Philips B6X12A

Hi Lee,
Quote:
Originally Posted by Hunts smoothing bomb View Post
Kat, I like your idea would that be just a small number of turns of wire around the core?
How many?
I'll let someone else answer that one. I could probably work it out and get it right but I don't trust my calculations all that well. Other members here have probably forgotten more about transformers than I'll ever know

To me, making a couple of autotransformers seems like the obvious answer, you don't need isolation as the existing transformers provide that. There's less wire to wind as there's only one winding involved, too.

I like to avoid modifying things if possible. So redefining the problem as "how can I match a modern 8-ohm or 4-ohm speaker to a set which expects an 800-ohm speaker" is what I'd be looking into if this was my set. (I'd probably look for a pair of car speakers which would fit.)

Cheers, Kat
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