12301 ?

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PLX
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Re: 12301 ?

Post by PLX »

Dave Friedman told me the filtering on Ed's 12301 was :

Two 100µF in series for the mains (200µF).
Two 32µF in series for the screens (64µF).
100µF on the phase inverter.
Two 32µF on the pre-amp taps.

:P
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harddriver
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Re: 12301 ?

Post by harddriver »

I found my Metro layout diagram the other day from the 12 Series instructions and the two 100uf axial cap are indeed in series which would make 200uf on the mains. The two screens 32uf axial caps are also in series would make 64uf on the screens.

There was some contention on Metro as to whether or not 12301 had 64uf or the 100uf PI filtering but if you look at the back of Ed's amp in the VHII pics it is a dual 50/50 can cap running at 100uf.

That would mean the Marshall actually reduced the filtering in 1969 to 50uf mains 50uf screens, 50uf/50uf preamp and 100uf PI.

At least you know you are not overfiltered on the mains at 100uf and are pretty much identical to 68 specs. ;)

I wanted to verify that the 69 Marshalls were indeed 50uf mains and 50uf screens and cames across this Metro thread...it's a good read.

http://forum.metropoulos.net/viewtopic.php?t=45387
Last edited by harddriver on Thu Jul 21, 2022 5:06 pm, edited 1 time in total.
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harddriver
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Re: 12301 ?

Post by harddriver »

PLX wrote: Thu Jul 21, 2022 4:06 pm Dave Friedman told me the filtering on Ed's 12301 was :

Two 100µF in series for the mains (200µF).
Two 32µF in series for the screens (64µF).
100µF on the phase inverter.
Two 32µF on the pre-amp taps.

:P
Did you have a recent email into Mr. Friedman?
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Re: 12301 ?

Post by PLX »

harddriver wrote: Thu Jul 21, 2022 5:04 pmDid you have a recent email into Mr. Friedman?
No.

He came over here to fix my BE-50 clone.

8-)
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Re: 12301 ?

Post by PLX »

harddriver wrote: Thu Jul 21, 2022 4:57 pm I found my Metro layout diagram the other day from the 12 Series instructions and the two 100uf axial cap are indeed in series which would make 200uf on the mains.
Right, and this is important for getting rid of the AC ripple once it's been rectified. This helps reduce noise throughout the entire amp.

harddriver wrote: Thu Jul 21, 2022 4:57 pmThe two screens 32uf axial caps are also in series would make 64uf on the screens.
I've tried different filtering here, and 64µF does something quite magical to the feel of the amp. I'll never change that filtering on the screens :!:

harddriver wrote: Thu Jul 21, 2022 4:57 pmThere was some contention on Metro as to whether or not 12301 had 64uf or the 100uf PI filtering but if you look at the back of Ed's amp in the VHII pics it is a dual 50/50 can cap running at 100uf.
I tend to believe what Friedman says about that, and he says it was the 50µF/50µF in series (total 100µF).
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