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
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
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.
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.
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".
No, it's just drawn wrong - VERY wrong
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?.
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.djgibson51 said:
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?
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.
What is drawn there is totally a fiction, born of error on the drawer.
Hi Guys
As stated above, this is just a poorly drawn schemo with a mistake. Soldano's effects returns are always to the grid of a tube. As usual, grid-stops are left out where they are most needed.
If you wanted to feed a signal into a cathode, the grid must be biased and so must be the cathode. There has to be a bias path and capacitive coupling must be used as the cathode will sit at a volt or so above ground. if you tried a direct connection as the erroneous drawing depicts, you would lose half the signal unless the signal was very small. The signal source would have to be a very low impedance.
Reverb returns were done like this very rarely, but the tank output is typically 100-200R DC and is like having a transformer drive. The circuit still benefits from having conventional bias components added and AC coupling.
Have fun
Kevin O'Connor
londonpower.com
As stated above, this is just a poorly drawn schemo with a mistake. Soldano's effects returns are always to the grid of a tube. As usual, grid-stops are left out where they are most needed.
If you wanted to feed a signal into a cathode, the grid must be biased and so must be the cathode. There has to be a bias path and capacitive coupling must be used as the cathode will sit at a volt or so above ground. if you tried a direct connection as the erroneous drawing depicts, you would lose half the signal unless the signal was very small. The signal source would have to be a very low impedance.
Reverb returns were done like this very rarely, but the tank output is typically 100-200R DC and is like having a transformer drive. The circuit still benefits from having conventional bias components added and AC coupling.
Have fun
Kevin O'Connor
londonpower.com
The Ampeg Reverberocket uses a grounded grid amp as a summing stage in an interesting configuration where the preceding (conventional) gain stage is coupled from it's cathode to the GG stage's cathode, and the grid is DC coupled to the output of the reverb recovery amp via a 15k reverb level pot. The phase relationship of the overall signal chain is such that the grid signal from the reverb return is additive to the "dry" signal on the cathode. The conventional stage also feeds the reverb driver amp from the plate side...all of which I thought to be quite clever.
The reason I found this thread is that I was curious about GG stages in guitar amps myself; I found it's the perfect opportunity in the R-12R for adding an effects loop, due to the low Z and the fact that the signal level is appropriate - just had to break the cathode-cathode connection and insert coupling caps and the loop jacks.
As a side note: the R12-R used DC coupling between the aforementioned cathodes (a 22k resistor) and this 50+ year old amp has it's share of noisy resistors. Adding DC blocking caps in series with the loop jacks served to eliminate some of the resultant noise, so that was a nice bonus and is probably a good practice for anyone considering using the cathode coupled GG arrangement as Ampeg did.
The reason I found this thread is that I was curious about GG stages in guitar amps myself; I found it's the perfect opportunity in the R-12R for adding an effects loop, due to the low Z and the fact that the signal level is appropriate - just had to break the cathode-cathode connection and insert coupling caps and the loop jacks.
As a side note: the R12-R used DC coupling between the aforementioned cathodes (a 22k resistor) and this 50+ year old amp has it's share of noisy resistors. Adding DC blocking caps in series with the loop jacks served to eliminate some of the resultant noise, so that was a nice bonus and is probably a good practice for anyone considering using the cathode coupled GG arrangement as Ampeg did.
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