1971 50 Watt - Mains fuse keeps blowing

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Loop-Master Pedals
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Re: 1971 50 Watt - Mains fuse keeps blowing

Post by Loop-Master Pedals » Fri Mar 08, 2019 10:36 am

Thanks for the test suggestion. I haven't gotten to it just yet but will as soon as I can. Thanks

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neikeel
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Re: 1971 50 Watt - Mains fuse keeps blowing

Post by neikeel » Sat Mar 09, 2019 7:12 am

jnew wrote:
Fri Mar 01, 2019 2:00 pm
neikeel wrote:
Fri Mar 01, 2019 1:36 pm
jnew wrote:
Fri Mar 01, 2019 1:30 pm
I had the diodes backards. :stars:

Amp sounds like the quintessential Marshall. It's killer. I don't know if anyone keeps track or has any interest in PT sag but I'm seeing 425V's on the plates and a big hard strum on an open E chord pulls the voltages down to about 310 or so. :what:
Write 1,000 lines "I must check diode polarity before soldering" and you will not do it again.
Sag is pretty typical.

Waiting for OP to chime back in.
Forgot to mark the schematic above up that the bias feed should be on the other side of the standby switch to that shown above so the bias circuit sees juice when on standby.
In the pics from above, are you suggesting that red wires from the PT and bias tap be placed on the bottom lugs of the switch while moving the blue wires to the rectifier to the top lugs?
As long as bias is connected directly to half the PT HT winding that will be correct.
Neil

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Re: 1971 50 Watt - Mains fuse keeps blowing

Post by jnew » Sat Mar 09, 2019 10:51 am

That's what I thought. Basically just want the bias "LIVE" when the power gets turned on. I wonder why the 100W amps were this way but not the 50W's. :what:
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neikeel
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Re: 1971 50 Watt - Mains fuse keeps blowing

Post by neikeel » Sat Mar 09, 2019 11:30 am

They were up to 69/70 and then again ear;y 70s (73 i think)
Neil

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