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Old 28th January 2009, 12:45 PM   #1
Trout is offline Trout  United States
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Default PI Question Guitar Amp Related

I was looking through old schematics the other night and came across an old Guild guitar amp .

I was wondering if anyone could share some insight on the PI in this model.

I am really curious about this one, I have never seen a PI implemented on other amps like this,

Pro's Con's ?
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Old 28th January 2009, 02:37 PM   #2
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Am I missing something? It just looks like a long tailed pair with paralled triodes to me.
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Old 28th January 2009, 02:42 PM   #3
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Quote:
Originally posted by leadbelly
Am I missing something? It just looks like a long tailed pair with paralled triodes to me.

Yeah, but why? 1 tube per side, paralled.

Does this drive the 6L6's better/harder?
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Old 28th January 2009, 03:04 PM   #4
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Better drive capability. Double the transconductance, half the plate resistance, and the 12AX7 is about the wimpiest around when it comes to driving. It all comes down to preference, because how the PI reacts when overdriven is a pretty characteristic sound of the amp. Actually, there's been a lot of interesting threads on paralleling triodes over the years, did you search? Some of the old boys who aren't around as much today had a lot to say.
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Old 28th January 2009, 04:21 PM   #5
Trout is offline Trout  United States
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Quote:
Originally posted by leadbelly
Better drive capability. Double the transconductance, half the plate resistance, and the 12AX7 is about the wimpiest around when it comes to driving. It all comes down to preference, because how the PI reacts when overdriven is a pretty characteristic sound of the amp. Actually, there's been a lot of interesting threads on paralleling triodes over the years, did you search? Some of the old boys who aren't around as much today had a lot to say.

I was reading a post on a guitar forum from a guy that recently picked up a Guild (not this model) So I looked up several schematics and noticed this one.

I have checked out hundreds of guitar amp schematics but never encountered one like this.

His comments on the model he has were very positive in regards to overdriven tone.
That was why I posted the question, It looks like it might be interesting to try.
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