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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 21st Oct 2017, 2:32 pm   #61
TonyDuell
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Default Re: Philips N4450

For those who are following this saga...

I eventually decided on the 3 core mains lead. I wired a short length to the machine (earth to the marked screw next to the mains input bush) and fitted it with the plug half of an in-line connector. A longer length from the socket part of the connector to a BS1363 plug (3A fuse, of course). And I did make up a short 2-core adapter cable I can put between them if I ever want the thing floating. But I consider removing safety earths to be the wrong way to cure earth loops, perhaps that should be a different thread...

I did check the insulation between the current-carrying wires and ground (with the unit's mains switch on, of course). Around 200MOhms at 1000V. So I am not worried that there's excessive leakage.

Time to try it out. Two nasty faults, the right channel was missing and some of the illumination bulbs went out when I pushed a DIN plug into one of the sockets. It was the force of doing that that slightly bent the amplifier motherboard that caused the bulbs to go out, nothing to do with the DIN plug being connected to anything.

That was due to a cracked track on the PCB that was trivial to cure once I had found it The lost channel was thost Philips slide switches again. I found the offending part (just has 6 terminals to switch the amplifier input between the tape recoder part (most modes) and the output of the 'before tape' pre-amp (in amplifier mode). So I desoldered it, cleaned the contacts again, and slightly bent the fixed contacts inwards. It now seems OK... I played back a scratch tape with no problems

Need to check recording on this machine. Also need to sort out a trim strip for the cover.
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Old 24th Oct 2017, 11:50 am   #62
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Default Re: Philips N4450

The latest on this machine. I found my old Philips headphones with the 5 pin 360 degree plug which are historically the right ones for this machine. I wired a couple of cheap microphones to 5 pin DIN plugs (why is there no standardisation as to the pinout of these, Philips and B&O use pin 1 for the signal, Uher uses pin 3...) and plugged everything it.

It works fine. I can record, play back, monitor off-tape etc. Never having used a machine with separate record and playback heads for microphone recording before, the delay between speaking and hearing the off-tape signal in the headphones took a bit of getting used to.

So I've put the covers back on. All that needs to be done to complete it is to make a trim strip for the plastic dust cover (I mentioned that many posts ago).
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Old 24th Oct 2017, 8:53 pm   #63
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Default Re: Philips N4450

Quote:
Originally Posted by TonyDuell View Post
I wired a couple of cheap microphones to 5 pin DIN plugs (why is there no standardisation as to the pinout of these, Philips and B&O use pin 1 for the signal, Uher uses pin 3...).
I seem to remember that on record, pin one was a low-level input and pin 3 could be used as high-level input....depending on how the product was wired. On playback, pin 3 was usually line level output. Pin 2 was the common chassis connection.
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Old 25th Oct 2017, 4:56 am   #64
TonyDuell
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Default Re: Philips N4450

Using pin 3 as a high level input on recording (with pin 1 a microphone-level input) was certainly done on some of the simpler Philips recorders with only one DIN socket for everything. This machine has separate microphone sockets (pins 3 and 5 not used) but I guess they wired it so that the same microphones could be used.
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Old 25th Oct 2017, 3:43 pm   #65
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Default Re: Philips N4450

Well done Tony, I hope you have a lot of fun with it. Those switches are pesky though, originally I was going to replace the A-B switch with a relay. In the end I just accepted that it could be intermittent and lived with it!

I seem to remember that to make use of the “tape” source/tape button on the Goodmans 1-10 it was necessary to make up a cable that used the “monitor” socket in addition to the DIN tape socket to obtain functionality. A straight 5 pin to 5 pin DIN cable would not work. Used the same solution for the N4504 and Grundig TK945. In the end made a custom switch box which also allowed to levels to match and dub between machines.

Peter.
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Old 25th Oct 2017, 8:11 pm   #66
TonyDuell
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Default Re: Philips N4450

Yes, since pins 3,5 of the tape DIN socket are used both for the outputs in playback mode and another input in record mode, you can't get an output there when you are recording. But as you say, you take the signal from the monitor socket.

If the switches were still available, I'd probably replace the lot. As it is, I have found it is best to remove the slider, clean that, spray contact cleaner into the body of the switch and carefully bend the fixed contacts inwards (press them from the outside with a small screwdriver or scriber point) before putting the slider back in.
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Old 25th Nov 2017, 7:38 pm   #67
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Yet another bit of tweaking. For cosmetic reasons I replaced the machine screws that fix the deck chassis to my new mouting blocks with slot head types (as all other screws in the machine have that sort of head). And I've put BC640 transistors in the flip-flops (in place of the original AC128s).

Still works fine, I think the BC640s are better here than 2N3906s as they have to handle the pinch roller solenoid current.
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Old 25th Nov 2017, 8:48 pm   #68
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Default Re: Philips N4450

Well, I am one small step nearer restoring mine, I bought some BC640s as suggested.

Another piece of N4450 trivia for you; the piece of trim surrounding the problematic sliding controls is held by either 6 or 10 screws. The earliest machines had the 6 screws, the upgrade to 10 was soon made in the production run.

Peter
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Old 26th Nov 2017, 7:43 am   #69
TonyDuell
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I got my BC640s from RS, you have to buy them in multiples of 50, but they are not at all expensive.

Do check the pinout of the BC640 before fitting it. Unlike the original AC128s and the 2N3906s it is not 'base in the middle'. I will try to get a photo in my flickr account over the next few days showing how they should be positioned.

I assume the trm you are talking about is the bit aroumd the switches at the top of the controls panel. Mine has 10 screws. And one of them goes into a bracket on the deck chassis and has to be removed to get the amplifier out. I think that's mentioned in the service manual.
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