Two different types of plate caps in use?

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dehughes
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Two different types of plate caps in use?

Post by dehughes »

Hi all,

On my Marshall JCM 2000 DSL 50, in parallel with the electrolytics on the 12AX7 plates I see they have ceramic caps of the same value. That is, the plates have both a 10uf electrolytic as well as a 10nf ceramic cap wired in. Never seen this before. What is the purpose of this?

Thanks in advance.
Last edited by dehughes on Wed Nov 01, 2017 8:19 pm, edited 1 time in total.
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sluckey
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Re: Two different types of plate caps in use?

Post by sluckey »

I see a 10nF in parallel with a regular 10µF electrolytic. The small cap is used because it reacts better for fast transients so it's more efficient at filtering fast noise spikes.
dehughes
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Re: Two different types of plate caps in use?

Post by dehughes »

sluckey wrote: Wed Nov 01, 2017 10:06 am I see a 10nF in parallel with a regular 10µF electrolytic. The small cap is used because it reacts better for fast transients so it's more efficient at filtering fast noise spikes.
Ah, sorry, thought that was "uf"...thanks.

So how is this "better", or, how does this setup express itself in tone and feel?
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tictac
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Re: Two different types of plate caps in use?

Post by tictac »

I don't think this is going to effect"Tone and Feel" as you say.... it's more about avoiding un-wanted noise artifacts, oscillations... etc. things that pop up in a high gain amp....


TT
dehughes
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Re: Two different types of plate caps in use?

Post by dehughes »

tictac wrote: Wed Nov 01, 2017 3:23 pm I don't think this is going to effect"Tone and Feel" as you say.... it's more about avoiding un-wanted noise artifacts, oscillations... etc. things that pop up in a high gain amp....


TT
Oh cool. Thanks.

I notice such caps are not used in "classic" Marshall-type circuits. Would removing these caps make any discernible, audible difference? I ask because I'm in full-on tinker mode with my DSL 50.
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sluckey
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Re: Two different types of plate caps in use?

Post by sluckey »

Pull 'em out. See what you think. Put 'em back in. That should satisfy your tinker mode for a while. :mrgreen:
dehughes
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Re: Two different types of plate caps in use?

Post by dehughes »

sluckey wrote: Wed Nov 01, 2017 4:07 pm Pull 'em out. See what you think. Put 'em back in. That should satisfy your tinker mode for a while. :mrgreen:
OH BELIEVE ME, I want to, but the older, wiser part of me says to ask here as you guys know more and can likely save me some effort.

(However, if no replies by noon PST today, then there's a good chance I'll just pull them out anyway.) ;)
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Stevem
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Re: Two different types of plate caps in use?

Post by Stevem »

I was gonna say, my God 10 uf ciramic s must be huge and act like a Microphone all on there own!
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sluckey
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Re: Two different types of plate caps in use?

Post by sluckey »

dehughes wrote: Wed Nov 01, 2017 5:00 pm (However, if no replies by noon PST today, then there's a good chance I'll just pull them out anyway.) ;)
So you default to the dark side. That's good... That's good... :twisted:
dehughes
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Re: Two different types of plate caps in use?

Post by dehughes »

Stevem wrote: Wed Nov 01, 2017 6:38 pm I was gonna say, my God 10 uf ciramic s must be huge and act like a Microphone all on there own!
Fixed, to avoid future confusion.
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pompeiisneaks
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Re: Two different types of plate caps in use?

Post by pompeiisneaks »

sluckey wrote: Wed Nov 01, 2017 8:19 pm
dehughes wrote: Wed Nov 01, 2017 5:00 pm (However, if no replies by noon PST today, then there's a good chance I'll just pull them out anyway.) ;)
So you default to the dark side. That's good... That's good... :twisted:
Let the hate flow through you! :P

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Ten Over
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Re: Two different types of plate caps in use?

Post by Ten Over »

Whenever I used a 0.1uF capacitor in parallel with the filter capacitor it was because V1 was like 35cm from the filter cap. The 0.1uF capacitor was not physically located right next to the filter capacitor as it was shown on the schematic. The 0.1uF capacitor was physically located at the V1 end of that 35cm antenna to shunt any noise it picked up to ground.
dehughes
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Re: Two different types of plate caps in use?

Post by dehughes »

Ten Over wrote: Thu Nov 02, 2017 4:09 pm Whenever I used a 0.1uF capacitor in parallel with the filter capacitor it was because V1 was like 35cm from the filter cap. The 0.1uF capacitor was not physically located right next to the filter capacitor as it was shown on the schematic. The 0.1uF capacitor was physically located at the V1 end of that 35cm antenna to shunt any noise it picked up to ground.
Interesting. These 10uf caps are right next to the filter caps, and maybe two inches from V1. I've ran much longer B+ leads in my handbuilt amps without issue, so I'm inclined to remove them and see whassup.
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dehughes
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Re: Two different types of plate caps in use?

Post by dehughes »

Removed them...don't notice much difference either way. Leaving them out as less is more, IMHO. :)
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