27nf Capacitors in Philips N4418 Speed control Circuit-is the value critical? - UK Vintage Radio Repair and Restoration Discussion Forum

'LIVEWIRE?' · 14th Sep 2010, 11:51 am

I suspect it is, because the two originals are 1% tolerance 63v yellow polyester(or similar)types. These need to be replaced, but none of the usual suppliers list 27nf capacitors(well RS stock SMD ones-no good for this machine!). The caps. in question are part of a differentiating circuit, wired in series with 470 ohm presets, one for each of the three speeds, the 27nfs being connected in Parallel for 1.875ips, in series for 3.75, and only one in circuit for 7.5. The machine runs too slowly if 33nf-the nearest value I had-are fitted, so I'm thinking of fitting 22nf/4n7(10% tolerance) types in parallel. As I have just fitted 3 new Piher enclosed presets in place of the original skeleton types I don't really want to change those again. Am I correct in thinking that the 'worst case' tolerance of the above would be + or - 20%?. Does anyone have, or know where I can get, some 1 or 2% 27nf capacitors?

AVO_VCM163 · 14th Sep 2010, 12:30 pm

If you can tolerate two in parallel, I can match and supply totally FOC if you pm me with address.
Roy

'LIVEWIRE?' · 14th Sep 2010, 6:57 pm

I'm sure they'll be OK, Roy. PM to follow shortly

david winter · 20th Sep 2010, 9:44 pm

Even if they're a bit out of the original tolerance, don't forget that you have individual timers to adjust the speed. Unless I mix that with the 4417.

Also, beware of a serious design fault in the 4450, just in case the 4418 has the same bug which can erase your tapes: in the 4450, the erase head is enabled not by a mecanical switch as usual, but by a stupid germanium transistor flip-flop (AC127/AC128). If one transistor gets shorted (which happens after all these years), the erase head will be enabled even in playback mode. As a result, you hear the tape very shortly and then nothing...

14th Sep 2010, 11:51 am	#1
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	27nf Capacitors in Philips N4418 Speed control Circuit-is the value critical? I suspect it is, because the two originals are 1% tolerance 63v yellow polyester(or similar)types. These need to be replaced, but none of the usual suppliers list 27nf capacitors(well RS stock SMD ones-no good for this machine!). The caps. in question are part of a differentiating circuit, wired in series with 470 ohm presets, one for each of the three speeds, the 27nfs being connected in Parallel for 1.875ips, in series for 3.75, and only one in circuit for 7.5. The machine runs too slowly if 33nf-the nearest value I had-are fitted, so I'm thinking of fitting 22nf/4n7(10% tolerance) types in parallel. As I have just fitted 3 new Piher enclosed presets in place of the original skeleton types I don't really want to change those again. Am I correct in thinking that the 'worst case' tolerance of the above would be + or - 20%?. Does anyone have, or know where I can get, some 1 or 2% 27nf capacitors?

14th Sep 2010, 12:30 pm	#2
AVO_VCM163 Retired Dormant Member Join Date: Mar 2008 Location: Hampshire, UK. Posts: 297	Re: 27nf Capacitors in Philips N4418 Speed control Circuit-is the value critical? If you can tolerate two in parallel, I can match and supply totally FOC if you pm me with address. Roy

14th Sep 2010, 6:57 pm	#3
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: 27nf Capacitors in Philips N4418 Speed control Circuit-is the value critical? I'm sure they'll be OK, Roy. PM to follow shortly

20th Sep 2010, 9:44 pm	#4
david winter Hexode Join Date: May 2008 Location: Paris, France Posts: 336	Re: 27nf Capacitors in Philips N4418 Speed control Circuit-is the value critical? Even if they're a bit out of the original tolerance, don't forget that you have individual timers to adjust the speed. Unless I mix that with the 4417. Also, beware of a serious design fault in the 4450, just in case the 4418 has the same bug which can erase your tapes: in the 4450, the erase head is enabled not by a mecanical switch as usual, but by a stupid germanium transistor flip-flop (AC127/AC128). If one transistor gets shorted (which happens after all these years), the erase head will be enabled even in playback mode. As a result, you hear the tape very shortly and then nothing...