1N4007 x4 or Bridge rec ? - UK Vintage Radio Repair and Restoration Discussion Forum

60 oldjohn · 10th Oct 2015, 12:47 pm

I have finally got round to looking at my Hacker mayflower RV14. The old Westinghouse FC124 rectifier has been removed and replaced with 4x 1N4007 and a resistor all very untidy and I intend tidying it up. 4x 1n4007 + resistor seems standard practice in this set.
1N4007 are quoted as 1A 1000v would a 2.5A 800v Bridge rec KBF-08 be ok? The sets HT is 275v max
I am aware of Mark Mhennessy great idea of hiding diodes and resistor in the old case, but as I have said original is long gone.

TFL John.

Herald1360 · 10th Oct 2015, 1:29 pm

That bridge will be fine. Max typical reverse voltage in a bridge diode is only peak ac in +/- a bit down to differing reverse leakage currents and even absolute worst case no more than 2Vpk.

60 oldjohn · 10th Oct 2015, 1:53 pm

Thank you Chris, I will get it put in.

John.

julie_m · 10th Oct 2015, 5:44 pm

The worst situation for a rectifier diode is actually a half-wave rectifier with capacitive smoothing. At the depth of the "trough", the capacitor connected to the cathode will be charged to the positive AC peak voltage; while the end of the transformer connected to the anode will be at minus that voltage. Thus imposing a reverse bias of twice the peak mains voltage (= 2 * RMS * sqrt(2); call it 3* the RMS voltage for the sake of round figures) across the rectifier.

A bridge rectifier constructed with 800V diodes will be absolutely fine, because the two reversed-biased diodes are in series and the PIVs add up.

10th Oct 2015, 12:47 pm	#1
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,988	1N4007 x4 or Bridge rec ? I have finally got round to looking at my Hacker mayflower RV14. The old Westinghouse FC124 rectifier has been removed and replaced with 4x 1N4007 and a resistor all very untidy and I intend tidying it up. 4x 1n4007 + resistor seems standard practice in this set. 1N4007 are quoted as 1A 1000v would a 2.5A 800v Bridge rec KBF-08 be ok? The sets HT is 275v max I am aware of Mark Mhennessy great idea of hiding diodes and resistor in the old case, but as I have said original is long gone. TFL John.

10th Oct 2015, 1:29 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: 1n4007 x4 or Bridge rec ? That bridge will be fine. Max typical reverse voltage in a bridge diode is only peak ac in +/- a bit down to differing reverse leakage currents and even absolute worst case no more than 2Vpk. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

10th Oct 2015, 1:53 pm	#3
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,988	Re: 1n4007 x4 or Bridge rec ? Thank you Chris, I will get it put in. John.

10th Oct 2015, 5:44 pm	#4
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: 1N4007 x4 or Bridge rec ? The worst situation for a rectifier diode is actually a half-wave rectifier with capacitive smoothing. At the depth of the "trough", the capacitor connected to the cathode will be charged to the positive AC peak voltage; while the end of the transformer connected to the anode will be at minus that voltage. Thus imposing a reverse bias of twice the peak mains voltage (= 2 * RMS * sqrt(2); call it 3* the RMS voltage for the sake of round figures) across the rectifier. A bridge rectifier constructed with 800V diodes will be absolutely fine, because the two reversed-biased diodes are in series and the PIVs add up. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.