Origin 20 scem????

[Valvehead]

Not sure why I cant find this...after 20 minutes searching pulling my hair out.

Marshall Origin 20.

If this is some super secret Nasa amp and you cant share the scem..........please....please........tell me the value of R7. I have 2 amps here--both have R7 burnt bad .

[fewa]

May be this will help. It is origin 50.

[alexradium]

i guess its a 10 or 100 ohm,you should see where its connected,if its between the 2 main filters probably 100

[alexradium]

in this pic it looks like 150 ohms

[alexradium]

yes its confirmed 150 ohms
https://youtu.be/mLhyrJUYJAo?t=119

[Valvehead]

THANKS !!!!!!!!!!!!!!

[drewl]

Seems like this is a good place to post this.

Working on one of these with intermittent power scaling. It looks like they use relays to change the high voltage, and in high power mode the amp has around 25v DC across R7, 150 ohms, when playing hard.
So that's over 4 watts from a 2 or 3 watt resistor.

This one is basically new and is already showing signs of R7 burning, so I'm going to replace it with a 5w

Just something to look out for when working on these.

[Valvehead]

Seems like this is a good place to post this.

Working on one of these with intermittent power scaling. It looks like they use relays to change the high voltage, and in high power mode the amp has around 25v DC across R7, 150 ohms, when playing hard.
So that's over 4 watts from a 2 or 3 watt resistor.

This one is basically new and is already showing signs of R7 burning, so I'm going to replace it with a 5w

Just something to look out for when working on these.

I did the same = 5w . Amps are working fine so far , 6 months later