Philips N4418 erase head query. - UK Vintage Radio Repair and Restoration Discussion Forum

Tractorfan · 25th Jan 2018, 5:47 pm

Hi,
I whipped the cover off this stereo deck today to change the belts, and I noticed that the two channels of the erase head are wired in anti-phase. Is there any particular reason for this? The record/play heads are, of course, wired in phase as per usual.
Cheers, Pete.

TonyDuell · 25th Jan 2018, 6:05 pm

The connections are shown like that on the wiring diagram page in the service manual, so your machine has not been 'got at'. The circuit diagram just labels the pins (a..d) and makes no indication as to the phase of the windings.

Actually, you don't _know_ that the 2 windings are wound the same way, so you can't be sure they are in antiphase (although I suspect you are right and they are). The erase heads on the (bidirectional) N4450 are wired the same way, so I guess there is reason for it.

It shouldn't matter as regards erasing the track the head is on, but I wonder if the idea was to reduce the stray field between the 2 heads and thus prevent erasure of the track between them (remember that the heads follow tracks 1, 3).

julie_m · 25th Jan 2018, 10:14 pm

Hmmmm ..... Interesting hypothesis. If they were fed in inverse phase, then the stray flux would tend to flow from one pole piece to the other one the same side of the gap, as opposed to shooting out if they were in equal phase .....

ricard · 26th Jan 2018, 9:36 am

Quote:

Originally Posted by TonyDuell

It shouldn't matter as regards erasing the track the head is on, but I wonder if the idea was to reduce the stray field between the 2 heads and thus prevent erasure of the track between them (remember that the heads follow tracks 1, 3).

Yes, I think that is exactly the reason, I remember reading that somewhere, can't remember where though.

hsbhachu3d · 29th Jan 2018, 3:25 pm

The winding in the head is done the other way round for the other channel. I ripped up a worn head and found it out the hard way lol

25th Jan 2018, 5:47 pm	#1
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Philips N4418 erase head query. Hi, I whipped the cover off this stereo deck today to change the belts, and I noticed that the two channels of the erase head are wired in anti-phase. Is there any particular reason for this? The record/play heads are, of course, wired in phase as per usual. Cheers, Pete. Attached Thumbnails __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

25th Jan 2018, 6:05 pm	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Philips N4418 erase head query. The connections are shown like that on the wiring diagram page in the service manual, so your machine has not been 'got at'. The circuit diagram just labels the pins (a..d) and makes no indication as to the phase of the windings. Actually, you don't _know_ that the 2 windings are wound the same way, so you can't be sure they are in antiphase (although I suspect you are right and they are). The erase heads on the (bidirectional) N4450 are wired the same way, so I guess there is reason for it. It shouldn't matter as regards erasing the track the head is on, but I wonder if the idea was to reduce the stray field between the 2 heads and thus prevent erasure of the track between them (remember that the heads follow tracks 1, 3).

25th Jan 2018, 10:14 pm	#3
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Philips N4418 erase head query. Hmmmm ..... Interesting hypothesis. If they were fed in inverse phase, then the stray flux would tend to flow from one pole piece to the other one the same side of the gap, as opposed to shooting out if they were in equal phase ..... __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

29th Jan 2018, 3:25 pm	#5
hsbhachu3d Pentode Join Date: Nov 2013 Location: Coventry, West Midlands, UK. Posts: 199	Re: Philips N4418 erase head query. The winding in the head is done the other way round for the other channel. I ripped up a worn head and found it out the hard way lol