Philips N4407 - UK Vintage Radio Repair and Restoration Discussion Forum

akaigxfan · 29th May 2014, 2:12 pm

Hello, working on yet another Philips N4407.
I'm noticing that the diodes that form the bridge rectifier aren't the ones that are on the schematic.
It says they should be 4 BY122 type then 2 BA148 later down stream, and 2 upstream. This machine also has the BA148 ones as the 4 for the bridge rectifier as well, so I'm just wondering are these the correct type and value? anyone help please? thanks.

ricard · 30th May 2014, 6:14 am

In general one would have thought that a small-signal diode from the BA series would not be a reasonable substitute for a rectifier diode (BY series). Looking at the data sheets though, the BA148 seems specified at a maximum forward current drop of 0.3A and the BY122 bridge at 0.6A, so these particular two are at least in the same ballpark.

Note: it seems the BY122 is actually a complete rectifier bridge rather than a single diode.

I found schematics for the N4407 on this page, which at least specifies 4x BA148 for the rectifier bridge.

My guess would be that either the BA148 was originally specified but was found to be used too close to or over its specification and replaced for that reason, or alternatively that the BY122 was originally specified but that the BA148 was cheaper and sufficiently reliable for this application. One would have to look in a complete service manual with change notes to see what was in fact the case.

akaigxfan · 30th May 2014, 9:50 am

Thanks for that ricard.

29th May 2014, 2:12 pm	#1
akaigxfan Retired Dormant Member Join Date: Jan 2012 Location: Whissonsett, Dereham, Norfolk, UK. Posts: 128	Philips N4407 Hello, working on yet another Philips N4407. I'm noticing that the diodes that form the bridge rectifier aren't the ones that are on the schematic. It says they should be 4 BY122 type then 2 BA148 later down stream, and 2 upstream. This machine also has the BA148 ones as the 4 for the bridge rectifier as well, so I'm just wondering are these the correct type and value? anyone help please? thanks.

30th May 2014, 6:14 am	#2
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: Philips N4407 In general one would have thought that a small-signal diode from the BA series would not be a reasonable substitute for a rectifier diode (BY series). Looking at the data sheets though, the BA148 seems specified at a maximum forward current drop of 0.3A and the BY122 bridge at 0.6A, so these particular two are at least in the same ballpark. Note: it seems the BY122 is actually a complete rectifier bridge rather than a single diode. I found schematics for the N4407 on this page, which at least specifies 4x BA148 for the rectifier bridge. My guess would be that either the BA148 was originally specified but was found to be used too close to or over its specification and replaced for that reason, or alternatively that the BY122 was originally specified but that the BA148 was cheaper and sufficiently reliable for this application. One would have to look in a complete service manual with change notes to see what was in fact the case. Last edited by ricard; 30th May 2014 at 6:29 am.

30th May 2014, 9:50 am	#3
akaigxfan Retired Dormant Member Join Date: Jan 2012 Location: Whissonsett, Dereham, Norfolk, UK. Posts: 128	Re: Philips N4407 Thanks for that ricard.