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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 14th Jul 2019, 8:53 pm   #21
Reelman
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Default Re: Philips N4450 Reel to Reel Tape Player

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I think at switch-on one of the 'direction' lamps should glow at low brightness showing the direction it was last used in.
Tony is absolutely right, on power on there should only be one of the two play lights on and dimmed. The stop button has no illumination.

Incidentally on power on both reels should rotate momentarily in opposite directions. This is to pick up any lack in the mounted tape.

Peter
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Old 14th Jul 2019, 9:00 pm   #22
Michael Maurice
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Default Re: Philips N4450 Reel to Reel Tape Player

I successfully repaired the flip flops on these using BC547’s and BC327’s.

The BC327’s have a similar current rating to the AC128’s and are pin for pin compatible
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Old 14th Jul 2019, 10:28 pm   #23
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Default Re: Philips N4450 Reel to Reel Tape Player

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The 'square PCB at an odd angle' sounds like the capstan motor electronics. It's mounted on the motor iteslf which drives the 2 capstans via a belt. I don't know if you are missing just the PCB or the complete motor assembly.
Yes that is correct.
It's actually part of the motor and was never available separately.

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Originally Posted by TonyDuell View Post
As an aside, some versions of the service manual give the circuit diagram for this part.
The 'Circuit Description' showed the circuits of the modules. It was available separately from the Service Manual which only showed the modules as blocks.
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Old 14th Jul 2019, 11:12 pm   #24
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Default Re: Philips N4450 Reel to Reel Tape Player

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I successfully repaired the flip flops on these using BC547s and BC327s.

The BC327s have a similar current rating to the AC128s and are pin for pin compatible
I'd have expected BC327s to be a good substitute in this application. I looked at the circuit and it only depends on the PNP polarity of the transistor, not the base-emitter voltage. The base-in-the-middle pinout makes it a very easy substitution.

A flip-flop fault could certainly cause your spurious recording lights problem. AC128s were once thought immune to Tin Whisker Syndrome, but apparently it just takes longer to show. Better to whip the lot out now than store up trouble for later.

As for why Philips used a germanium transistor: They were still making them in the 1970s, and they probably were cheaper than a similarly-rated silicon PNP transistor (it's harder to dope silicon to P-type than N-type; germanium is the opposite).
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Old 15th Jul 2019, 7:45 am   #25
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Default Re: Philips N4450 Reel to Reel Tape Player

Thank you experts. I have noted the transistors you have mentioned and have seen that these are under 2 delivered via ebay.

There are lots of spares available on Ebay today - even a capstan motor board....

https://www.ebay.co.uk/sch/i.html?_f...N4450&_sacat=0
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Old 15th Jul 2019, 8:58 am   #26
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Default Re: Philips N4450 Reel to Reel Tape Player

Quote:
Originally Posted by Reelman View Post
Quote:
Originally Posted by TonyDuell View Post
I think at switch-on one of the 'direction' lamps should glow at low brightness showing the direction it was last used in.
Tony is absolutely right, on power on there should only be one of the two play lights on and dimmed. The stop button has no illumination.

Incidentally on power on both reels should rotate momentarily in opposite directions. This is to pick up any lack in the mounted tape.

Peter
Thanks Peter - Yes, I initially found this odd that on power up the reels rotated in opposite directions, but now understand why. Machine 1 does this.
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Old 15th Jul 2019, 4:31 pm   #27
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Default Re: Philips N4450 Reel to Reel Tape Player

Sorry for all the questions - but If i want the machine to run properly and i want to try and fix it myself, where should I start?

I guess that replacing all the common fault transistors is a good place to start.

Replace all AC128s with BC327's
Replace all xxxx with BC 547's

Anything else?

My:
flip flops have BC147's.
tape tension is BC 147's.
auto rev is 157's and BC547
motor stop is BC557 BC547
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Old 15th Jul 2019, 9:53 pm   #28
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Default Re: Philips N4450 Reel to Reel Tape Player

My advice is to replace the AC128s with BC327s then test everything. By and large the BC147s will be ok but if you suspect them, fit BC547s.

I would not attempt to replace transistors for the sake of it. The AC128s are known troublemakers but the rest are not and you might end up with more problems than when you started.
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Old 16th Jul 2019, 7:22 am   #29
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Default Re: Philips N4450 Reel to Reel Tape Player

Sorry Michael. On which board are the AC128's? I cant see them, but i do need some new glasses.....
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Old 16th Jul 2019, 8:54 am   #30
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Default Re: Philips N4450 Reel to Reel Tape Player

They are on the flip flop boards, there are 4 on each board and are recognisable by their metal can.
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Old 17th Jul 2019, 7:57 pm   #31
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Default Re: Philips N4450 Reel to Reel Tape Player

BC 327's ordered and will arrive on Friday - 20pcs for 3.98 delivered...

Apologies for external linked images, but what is missing here?

https://i.imgur.com/yUk9J8G.jpg

Do i need this part?
https://www.ebay.co.uk/itm/PHILIPS-N...2329%7Ciid%3A1

https://i.ebayimg.com/images/g/oXUAA...GX/s-l1600.jpg
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Old 18th Jul 2019, 10:48 am   #32
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Default Re: Philips N4450 Reel to Reel Tape Player

BC 327s have arrived and I am keen to get on and replace.

The AC128 data sheets i have shown that the component should have a tab on the metal case. Mine dont.
Is the red spot (or black spot on some of them) marking the emitter?
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Old 18th Jul 2019, 2:27 pm   #33
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Default Re: Philips N4450 Reel to Reel Tape Player

All the AC128's I've ever seen don't have a tab and the red spot marks the collector. The AC127...the NPN counterpart has a dark blue spot that marks collector
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Old 18th Jul 2019, 5:45 pm   #34
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Default Re: Philips N4450 Reel to Reel Tape Player

Thanks Sideband - If im feeling brave, I will try to replace all 8 across two machines tomorrow (16 in total).

Some of mine have a blue dot. Does that mean that they are NPN and cannot be replaced by the BC327s?

Last edited by Ray_Singh; 18th Jul 2019 at 6:00 pm. Reason: NPN Vs PNP
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Old 18th Jul 2019, 7:43 pm   #35
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Default Re: Philips N4450 Reel to Reel Tape Player

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Some of mine have a blue dot. Does that mean that they are NPN and cannot be replaced by the BC327s?
Well.....if they are marked AC128 then they should be OK. If they are originals as fitted by Philips then they will be AC128.

The original flip flops had AC128 and BC148 (or BC548) fitted so PNP germanium and NPN silicon. NEVER NPN germanium.

Why not post a picture of one of your flip flops?
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Old 19th Jul 2019, 7:52 am   #36
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Default Re: Philips N4450 Reel to Reel Tape Player

I have had some AC128's that have a slightly thinner can and a tab, a bit like an elongated BC107.
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Old 19th Jul 2019, 9:56 am   #37
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Default Re: Philips N4450 Reel to Reel Tape Player

Thank you.

Flip Flop photo:
https://i.imgur.com/kkacDvx.jpg
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Last edited by Michael Maurice; 19th Jul 2019 at 1:48 pm. Reason: addition of picture
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Old 19th Jul 2019, 7:24 pm   #38
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Default Re: Philips N4450 Reel to Reel Tape Player

Yes...the AC128's as I remember them....red spot marks collector. If you are not aware, those BC147 lockfits are now becoming unreliable.....They can be replaced directly by BC547 which is the same transistor in a different package, also has the same lead configuration. Chances are almost any NPN transistor with a similar gain could be used but watch the lead configuration.
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Old 20th Jul 2019, 4:37 pm   #39
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Default Re: Philips N4450 Reel to Reel Tape Player

Thanks Sideband.

I spent a bit of time fiddling with the machine today. I swapped the flip flop boards around between machine 1 and machine 2 and from top to bottom.
I finally got the record button to switch off and the old tapes i have are actually playing!! I cant hear them as i have no DIN connectors, but i can see the VU meters fluctuating!

I am so excited.

I will use the "spare" flip flop boards as a starting point to swap out the AC128s to BC327s and see how i go from there.

The capstan motor will be here next week too!
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Old 22nd Jul 2019, 11:42 am   #40
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Default Re: Philips N4450 Reel to Reel Tape Player

Capstan motor arrived.

I have managed to hear the tape playing from machine 1. I dont have any of the odd speaker connectors, so plugged in a DIN from the monitor output into my own home amplifier. I can hear tapes i recorded 25 years ago!

I managed to screw up the power on/off switch on both machines. Does anyone have spare please?
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