Diodes and SCR's old/ new replacements - UK Vintage Radio Repair and Restoration Discussion Forum

Levente · 14th Jun 2020, 2:32 pm

Hey Guys,

Refurbishing an old delay unit.

Please, advise me on some replacement possibilities on the following:

1. Diodes. Can a 1N5404 (or MR501) be replaced to a higher voltage/value one? MR506 for example? I have these in my drawer but the unit has 1N4004's in the -5V circuit..

2. SCR. Someone during the years installed 2n6403 for at the -5V and i think the -12V seems to be there too. The manual (sadly I can not hold of any schemantics on th enet for this LExicon Delta T 102 model) referring to an old 2N681 thyristor) at this place. Comparing the values of the two, there are massive differences in values..

What could be a suitable replacement for this thyristor?

Many many thanks for your advise...the only piece of information I have with regards this is attached..

TrevorG3VLF · 14th Jun 2020, 6:10 pm

1. A 1N4004 is a 1A diode, I would go for a 1N4007 to avoid keeping lower voltage ones. Similarly for the higher current 1N540x.
Replacing diodes with those of higher capability is OK if rhe fatter leads will pass through the PCB holes.

2.SCRs. In a similar way to diodes, components with higher capability should be OK but the more powerful SCRs need a bigger gate current to turn them on.

Show us the specifications of the components you have. I do not want to spend time looking for them and I only have one brain cell left.

Levente · 15th Jun 2020, 7:58 am

Quote:

Originally Posted by TrevorG3VLF

1. A 1N4004 is a 1A diode, I would go for a 1N4007 to avoid keeping lower voltage ones. Similarly for the higher current 1N540x.
Replacing diodes with those of higher capability is OK if rhe fatter leads will pass through the PCB holes.

2.SCRs. In a similar way to diodes, components with higher capability should be OK but the more powerful SCRs need a bigger gate current to turn them on.

Show us the specifications of the components you have. I do not want to spend time looking for them and I only have one brain cell left.

Hi Trevor, thanks a lot. Really appreciate your time.

1. What I have in the unit is an MC2N6403 attached the pdf info of it. Here the gate trigger current is 30-60mA.

2. What I have for replacement is either 2N6509 or 2N6505 with the peak reverse and forward voltages 800V or 500v and the gate trigger current is 40-75mA.

With regards the diodes, i have these two, took a pic of them and I don't know what are they... this must have been replaced by someone earlier. The little green on has "53" on it the other I can not make it out, but both could be a value of either 1N4004 or 1N5404 referring to the user manual posted earlier? This is where I am getting confused a bit..

Thanks again,

Best
Levi

14th Jun 2020, 2:32 pm	#1
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	Diodes and SCR's old/ new replacements Hey Guys, Refurbishing an old delay unit. Please, advise me on some replacement possibilities on the following: 1. Diodes. Can a 1N5404 (or MR501) be replaced to a higher voltage/value one? MR506 for example? I have these in my drawer but the unit has 1N4004's in the -5V circuit.. 2. SCR. Someone during the years installed 2n6403 for at the -5V and i think the -12V seems to be there too. The manual (sadly I can not hold of any schemantics on th enet for this LExicon Delta T 102 model) referring to an old 2N681 thyristor) at this place. Comparing the values of the two, there are massive differences in values.. What could be a suitable replacement for this thyristor? Many many thanks for your advise...the only piece of information I have with regards this is attached.. Attached Thumbnails

14th Jun 2020, 6:10 pm	#2
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Diodes and SCR's old/ new replacements 1. A 1N4004 is a 1A diode, I would go for a 1N4007 to avoid keeping lower voltage ones. Similarly for the higher current 1N540x. Replacing diodes with those of higher capability is OK if rhe fatter leads will pass through the PCB holes. 2.SCRs. In a similar way to diodes, components with higher capability should be OK but the more powerful SCRs need a bigger gate current to turn them on. Show us the specifications of the components you have. I do not want to spend time looking for them and I only have one brain cell left.