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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 31st Oct 2018, 8:12 am   #1
suebutcher
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Default Philips N4407 etc double insulated?

Sorry if I've asked this before, but are the Philips N4400 series tape recorders properly double insulated? My N4407 came with the typical Philips two-core mains lead, but despite the lack of earthing, most of the metal trim and some of the knobs on the front panel are electrically connected to the chassis. That's not good practice is it?

And speaking of the mains lead, does anyone have an image of the mains stowage cover panel on top of the machine? These are almost always missing, and I'd like to try making one.
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Old 31st Oct 2018, 8:53 am   #2
TonyDuell
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Default Re: Philips N4407 etc double insulated?

They are _supposed_ to be double insulated, but I am not convinced...

One problem is that they may be earthed via the screening of the audio cables and whatever amplifier you connect them to. Which means that if the recorder is earthed as well you get an earth loop and thus hum.

When I repaired my N4450, I fitted a 3 core cable with the earth wire going to a tapped hole on the mains input bracket labelled with the earth symbol. I fitted an in-line cable connector as the hole in the rear panel was not large enough for the UK plug to fit through, meaning that I could not easily remove this panel for repairs (having it dangling on the cable was a pain). I then made up a 2-core cable with a similar in-line connector on the ends. I can fit this between the mains plug to in-line connector socket cable and the in-line plug on the machine if I don't want it earthed via the mains plug for any reason.
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Old 31st Oct 2018, 1:12 pm   #3
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Default Re: Philips N4407 etc double insulated?

I'll be using it mostly as a free standing tape player, so I'll fit a three-core earthed mains lead.

No earth and dubious insulation seems to be the norm for hifi equipment. I checked my sound system the other day, and none of it is earthed; each component is designed on the assumption that something else it's connected to will be earthed! I'll add an earth to the amplifier if possible.
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Old 31st Oct 2018, 5:55 pm   #4
TonyDuell
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Default Re: Philips N4407 etc double insulated?

I really dislike the idea that the screen of the audio cable should be the safety earthing conductor. It can be disconnected too easily, and may not carry the current anyway. I wonder why balanced (differential) inputs are not common on hi-fi amplifiers. This would go a long way to solving the earth loop problem. But anyway.

Some valve tuners which drew their HT+ voltage from the main amplifier used the audio cable screen as the HT return. Meaning that if you unplugged the audio cable the tuner chassis would get up to the HT+ voltage (albeit somewhat current-limited) relative to the amplifier chassis. ARGH!
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Old 31st Oct 2018, 6:42 pm   #5
Ted Kendall
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Default Re: Philips N4407 etc double insulated?

Ground sensing inputs are fairly trivial these days with op-amps, but I suppose the tradition just grew up in earlier times, with earth loops the major perceived problem. Even with studio kit, the number of manufacturers who didn't understand that Pin 1 of the XLR was to go to chassis and nowhere else boggles belief.
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Old 1st Nov 2018, 8:46 pm   #6
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Default Re: Philips N4407 etc double insulated?

Photos of the cover if you still need them. Actually from a Pye 9137 which I believe is identical.

Roy
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Old 4th Nov 2018, 11:35 am   #7
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Default Re: Philips N4407 etc double insulated?

Thanks Roy. I think I could make something like that from sheet styrene and paint it to match. The N4407 part is dark brown like the rest of the bottom case.
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Old 4th Nov 2018, 4:07 pm   #8
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Default Re: Philips N4407 etc double insulated?

Sue I think I have one of those you can have if you pay the shipping , I`ll have a look in a bit .

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Old 5th Nov 2018, 12:55 pm   #9
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Default Re: Philips N4407 etc double insulated?

Wonderful! Let me know if you find it.
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Old 6th Nov 2018, 10:52 pm   #10
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Default Re: Philips N4407 etc double insulated?

I have one Sue but there appears to be something missing off the catch , looks like there should be something holding the catch on . The catch just falls out of this one , you are welcome to it though I`m sure it can be sorted some how.

I`ll post some pics in a sec

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Old 6th Nov 2018, 10:58 pm   #11
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Default Re: Philips N4407 etc double insulated?

pic set 1
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Old 6th Nov 2018, 11:00 pm   #12
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Default Re: Philips N4407 etc double insulated?

If you look at these two pics , you need to stop those long bits going thround those holes , so a small plate and then melt them maybe ?
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Old 7th Nov 2018, 2:12 am   #13
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Default Re: Philips N4407 etc double insulated?

this is from the pye 9137 but as someone else said i thing they are the same.
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Old 7th Nov 2018, 4:24 am   #14
Maarten
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Default Re: Philips N4407 etc double insulated?

Quote:
Originally Posted by suebutcher View Post
I'll be using it mostly as a free standing tape player, so I'll fit a three-core earthed mains lead.

No earth and dubious insulation seems to be the norm for hifi equipment. I checked my sound system the other day, and none of it is earthed; each component is designed on the assumption that something else it's connected to will be earthed! I'll add an earth to the amplifier if possible.
Fixed metal parts that are at least 4 to 5kV of dielectric strength removed from the mains count as double insulation. I'm not convinced there is any kind of assumption that something else will be earthed. You don't want to have earth loops on audio equipment.
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Old 7th Nov 2018, 10:37 am   #15
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Default Re: Philips N4407 etc double insulated?

Posh hifi often has an earth terminal so that there is an option to earth it at any pace that gets rid of hum.
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Old 9th Nov 2018, 6:37 am   #16
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Default Re: Philips N4407 etc double insulated?

Quote:
Originally Posted by NorfolkDaveUK View Post
this is from the pye 9137 but as someone else said i thing they are the same.
Thanks. It looks usable, I'll PM you shortly.
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