Help with diode bridge and bias supply wiring

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Kennetiversen
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Location: Åsen, levanger

Help with diode bridge and bias supply wiring

Post by Kennetiversen » Fri Aug 04, 2017 7:26 am

Hi!

Just aquired a broken marshall jcm 800 4210. I ordered a ptp 2204 board from a guy named Walt from Ebay.

I have installed the board using this layout: http://imagizer.imageshack.us/a/img923/7464/csvXym.jpg

This is the layout for my ptp: http://imageshack.com/a/img924/2359/LcsqP6.jpg

Now... I discovered that my PT did not have an Center tap and that i have to go for a full bridge rectifier and change the bias circuit a bit.

Here is a picture of the actuall board: http://imageshack.com/a/img922/4094/8XNscd.jpg

Can somebody please give me a step by step on what to do?

Best regards :rock:

Kennet
Kennet Iversen

Kennetiversen
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Joined: Sat May 17, 2014 3:22 am
Just the numbers in order: 13492
Location: Åsen, levanger

Re: Help with diode bridge and bias supply wiring

Post by Kennetiversen » Fri Aug 04, 2017 7:43 am

This is what I have done so far: http://imageshack.com/a/img924/3291/9GgeW8.jpg
Kennet Iversen

marshallnoise
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Re: Help with diode bridge and bias supply wiring

Post by marshallnoise » Wed Oct 25, 2017 3:58 pm

marshallnoise wrote:
Mon Sep 18, 2017 7:14 pm
Seems like something at the bottom of the page would make sense. Am I correct in thinking that half of the rectifier will be seeing AC all the time and the other half will get it when the standby switch is flipped?
http://www.valvewizard.co.uk/standby.html
So this is what I had to do for the standby switch wiring.

If you have no centertap on your HT, then you have to do a capacitor coupled bias supply.
Littlewyan wrote:
Thu Sep 14, 2017 7:33 am
Because you have no centre tap on the HT you will need to use a Capacitor Coupled Bias Supply.

http://valvewizard.co.uk/bias.html

Merlin explains it here. It's an odd circuit and you will have to wire up the standby switch a bit differently for it to work properly when the amp is in standby. Also for safety reasons you may want to use a special capacitor. One that is rated for high AC Voltage and I think it shorts when it fails or something? I bought a few. Marshall have used this circuit a few times and I used it in my last build. I can give further details in a few days time if you need them :).
And here is the way it is wired up for me.
ImageIMG_20171024_082925017 by Paul Abbott, on Flickr

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