LOUDthud wrote:As I said in my previous post, you need the cap coupled bias supply because of the full wave bridge.
Understood...
What I have now is like this(bottom of bridge is grounded and replaced 15k with 220k)
Is what you are saying is more like the top of the pdf page?
Darin
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tried my interpretation of the cap coupled bias supply
and still no go...bias just jumps to over 100ma quick
not sure what's wrong...tubes,bias cap?
Pic of the PS board as is.
Sorry this is taking so long to figure out.Learning how little I know about
different power and bias circuits. Suggestions are appreciated.
Darin
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Marshall uses the cap coupled circuit in a couple of their amps in the JCM900 series. They use a .047uF cap specified "Class X" and a 56K resistor before the bias rectifier.
How is your Standby switch wired? You need to make sure that the bias supply still works when the Standby switch is in the non-play position. Don't turn the Standby to Play unless you have good bias voltage at the tubes.
LOUDthud wrote:Marshall uses the cap coupled circuit in a couple of their amps in the JCM900 series. They use a .047uF cap specified "Class X" and a 56K resistor before the bias rectifier.
How is your Standby switch wired? You need to make sure that the bias supply still works when the Standby switch is in the non-play position. Don't turn the Standby to Play unless you have good bias voltage at the tubes.
Thanks LOUDthud
I did not know the bias should work in standby...
I have the B+ side of rectifier going to standby switch then to filter caps
Can I just break one side of the secondary taps with the standby switch
instead? Or do I need a standby switch at all?
Darin
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I think you are ok the way you have described it with the switch on the filter side of the bridge. The Marshall schematic you posted might not work (when the amp is in Standby) unless the coupling cap is moved to the side with the switch.
LOUDthud wrote:I think you are ok the way you have described it with the switch on the filter side of the bridge. The Marshall schematic you posted might not work (when the amp is in Standby) unless the coupling cap is moved to the side with the switch.
appreciate your time
so I only move the .047 cap to the switch side or move the switch to the
bias circuit side?
