Thread: Philips N4450
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Old 5th Aug 2017, 2:23 pm   #25
TonyDuell
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Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
Default Re: Philips N4450

A (small) progress report :

I finally got round to plugging it into the mains. At power-on the control system went crazy, and the left spool motor squealed like mad. To avoid problems there I powered down, pulled out the 2 flip-flop boards and powered up again.


All the switch illumation lamps came on, so did the 2 for the level meters (and the track switch controls them). The clock motor was running nicely. The capstan motor was running (with no belts obviously the capstans weren't turning), and the speed control switch does just that. Obviously I don't know if the speeds are correct but it runs.

I removed all 8 AC128s from the flip-flop boards and replaced them with 2N3906s. Maybe a bit marginal, but if they fail I can fit something with a higher maximum Ic. Put the flip-flops back in. Also removed the pulley from the left spool motor, cleaned it and put a drop of light oil on the bearing thus exposed. Powered up again. The control system seems fine, the motors and solenoids seem to run when they should. I will order a belt kit.

I've tried connecting a pair of cheap-n-nasty speakers to it. There is more background noise than I would like, probably due to the lockfit transistors. As I can easily get T092-cased versions (as I understand it, the BC547 is the same transistor as the BC147, just in a different package) I will get some. In AMP mode (by-passing the tape unit), the left channel gain seems much lower than the right. Maybe lockfit transistor problems again. I think the way to sort that out is to put a signal generator on the input and trace signals with a 'scope.

The good news is that in play mode (actually stop mode, since the electronics is set to play in that state), I get a buzz from each speaker when I bring my old demagnetiser up to the heads. Again left channel is quieter. Also works after selecting right-to-left mode and stopping it again. So the replay heads look to be doing something.
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