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-   -   Grounded grid stage in guitar amp (http://www.diyaudio.com/forums/instruments-amps/219364-grounded-grid-stage-guitar-amp.html)

djgibson51 9th September 2012 01:56 AM

Grounded grid stage in guitar amp
 
I'm trying to figure out the effect of the grounded grid (effects return) stage in the soldano super lead 60 schematic I found at EL34world.com.

Also, the following triode is a puzzle. It has a 100k resistor on both anode & cathode with grid connected to previous grounded grid anode at B+.

What happens in these 2 triodes as they overload?

JimG

djgibson51 9th September 2012 02:03 AM

1 Attachment(s)
Here is a pdf of the schematic. V3 a&b have me intrigued.
JimG

jjman 9th September 2012 03:47 AM

That can't be correct I believe. It would put dc on the effect return from the cathode side of R18. I suspect a schematic switcharoo. Not an official one right?

benb 9th September 2012 04:50 AM

I agree about the DC, and more, I guarantee that schematic is wrong. Even if the return were meant to be a "cathode input" the plate goes directly to B+ and so there's no signal going to the grid ofV3b.

Now I see the disclaimer about accuracy in the lower left corner.

If there's a forum at that site, ask there. Someone may have a corrected version of the schematic.

DF96 9th September 2012 02:43 PM

Either a deliberate spoiler, or very clumsy reverse engineering. V3a grid and cathode have been swapped, and R21 should be in V3a anode not V3b anode.

tubelab.com 9th September 2012 06:46 PM

Quote:

very clumsy reverse engineering.
I have never seen a Soldano schematic with their name on it. I suspect that all the Soldano schematics on the net are reverse engineering derived. That one has the previously mentioned obvious mistakes. I have another (different) Soldano schematic on my hard drive somewhere that has a few questionable "features".

djgibson51 10th September 2012 09:19 AM

So soldano doesn't have a magic grounded grid stage. Can a gg be overdriven? What would that look like? Wouldn't have grid current limiting.
Ever been used in a guitar amp?

Nigel Goodwin 10th September 2012 10:19 AM

Quote:

Originally Posted by djgibson51 (Post 3158940)
So soldano doesn't have a magic grounded grid stage.

No, it's just drawn wrong - VERY wrong :D

Quote:


Can a gg be overdriven? What would that look like? Wouldn't have grid current limiting.
Ever been used in a guitar amp?
I wouldn't have thought so - I can't see any need (or advantage) in ever doing so?. Grounded grid gives you a low input impedance and a high output impedance, neither of which are of any value in a guitar amp.

You could certainly overload gg just as with any configuration, I don't know as it would make any difference or not?.

DF96 10th September 2012 12:13 PM

Quote:

Originally Posted by djgibson51
So soldano doesn't have a magic grounded grid stage. Can a gg be overdriven? What would that look like? Wouldn't have grid current limiting.
Ever been used in a guitar amp?

I have never seen a magic grounded grid stage. Ordinary grounded grid stages are often used in valve-based UHF receivers such as 1960s TV sets.
Yes, a gg stage can be overdriven. I presume it would cause signal clipping.
My guess is that gg has never been used in a guitar amp, except possibly by accident - someone blindly copying a bad case of reverse engineering?

Enzo 10th September 2012 09:18 PM

Look at the parts. Someone confused the two triodes. R21 and R19 belong to the left triode, plate and cathode. R18 and return signal go to the grid, not cathode. SO the right triode plate goes to B+. And step back and you have a VERY conventional gain stage with 1 meg grid return, a 1k cathode and 100k plate load. Plate direct coupled to VERY conventional cathode follower driving the tone stack.

What is drawn there is totally a fiction, born of error on the drawer.


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