Some question about Mark IV's schematic

[ironlung]

Ohh, why can't upload a graph.

When in R1 R2 mode, both the LDR10 and the LDR8 are opened, if the LDR11 or LDR12 putting to earth is necessary? Because the LDRs isn’t reslly opened, but indeed a large velue resistor?

When R2 mode, the RY1 is closed, if the LDR11xx is necessary? Both close? If the LDR11xx is excrescent?

Would somebody kind tell me? Thank you very much!!

 

[Boogiebabies]

An LDR does need an extremely high dark resistance to keep the circuit from bleeding or in essence keeping the cell closed. Having relay closed on the R2 IMO is a misnomer as it is only engaging the mid gain circuit which we all know only works on the lead channel. Using LDR's as shunt with groung reference like LDR 11, 11X and 12 obviously do not show anything but the use if the 10M dark resistance when shunted/closed. What we never see on Mesa shematics is the second side of the trace or the switching buss.

So for that, you need to think of how it is accomplished.

With that, here is the function of a few LDR's in question and relays in the circuit. To fully realize the method of the switching matrix you have to study it and try to see if your get your answers. If you know about LDR11X you probably have the truth table and LDR functions, but you have to look at the unseen second trace. Some of these are done simply to isolate circuits, switching and possibly to make a quieter amp.


RY1 - Mid Gain Engage
RY2- 47pf / 680K ground reference
LDR8- Lead Drive on
LDR9- R2 Gain On
LDR10- Lead Output ON
LDR11- Lead Output Shunt R2
LDR11X - R2 FX Shunt (4.7K)
LDR12- Lead Output Shunt

After years of looking at Mesa schematics, I stopped asking "Why".

Have fun trying to figure this mess out.

 

[ironlung]

Thank you very much!!!!!
I got the whole schematic(including the power supply, the switching busses and the foot switch) and study it for a while. I don't understand "the second side of the trace" that you said, is there some more schematic about Mark IV?
I list the LDRs and Relays turn on in every mode, so is that right?

MODE.............Turn On(ON Resistance)

R1..................RY1(R1) LDR5 LDR12 RY2(R1、L) LDR15 LDR22

R2..................LDR7 LDR6 LDR2 LDR9 RY2(R2) LDR11 LDR14 LDR11x LDR21

LEAD..............LDR4 LDR8 RY2(R1、L) LDR10 RY1(R2、L) LDR13 RY1(R2、L) LDR20

The LDR11x turn on in R2 mode shunt a portion signal with ground, because the signal level in R2 mode (as well as in LEAD mode) from tube V2A is much higher than in R1 mode?
And is there some relation between the LDR11 and LDR11x? Why one call 11 and other call 11x?
I hope I own a Mark IV, but I don't.
At last, thanks again!!!

 

[Boogiebabies]

The second trace is the switching matrix circuit. What you do not see is the circuit on how all of the switching and logic is implemented. LDR 11X is probably a dual element that allows one LDR to switch two different functions. I would really like to check LDR 11 and 11X, but I do not feel like pulling the chassis so close to kickoff time.

 

[michelj]

Thank you very much!!!!!
I got the whole schematic(including the power supply, the switching busses and the foot switch) and study it for a while. I don't understand "the second side of the trace" that you said, is there some more schematic about Mark IV?
I list the LDRs and Relays turn on in every mode, so is that right?

MODE.............Turn On(ON Resistance)

R1..................RY1(R1) LDR5 LDR12 RY2(R1、L) LDR15 LDR22

R2..................LDR7 LDR6 LDR2 LDR9 RY2(R2) LDR11 LDR14 LDR11x LDR21

LEAD..............LDR4 LDR8 RY2(R1、L) LDR10 RY1(R2、L) LDR13 RY1(R2、L) LDR20

The LDR11x turn on in R2 mode shunt a portion signal with ground, because the signal level in R2 mode (as well as in LEAD mode) from tube V2A is much higher than in R1 mode?
And is there some relation between the LDR11 and LDR11x? Why one call 11 and other call 11x?
I hope I own a Mark IV, but I don't.
At last, thanks again!!!

hello Ironlung,

I sent you a PM with my email address because I'm interested in getting a soft copy of the power supply, the switching busses and the foot switch schematics. It would be great if you could oblige.

Thanks in advance Michel

 

[ironlung]

Thank you Boogiebabies!
I understand the swithing matrix circuit presumedly, but not sure
And I know there is dual cell LDR, one LED control two LDR, so since LDR11 is independent from LDR11x, if it is a dual cell LDR or two individual is nonsignificant.
I need a help, some clear inside picture, had best with commentate
Do any DIYer own a Mark IV, and would you please do me the favore?
I appreciate your kindness, thank you.

Michelj friend, I'll send you soon.

 

[Boogiebabies]

Thank you very much!!!!!
I got the whole schematic(including the power supply, the switching busses and the foot switch) and study it for a while. I don't understand "the second side of the trace" that you said, is there some more schematic about Mark IV?
I list the LDRs and Relays turn on in every mode, so is that right?

MODE.............Turn On(ON Resistance)

R1..................RY1(R1) LDR5 LDR12 RY2(R1?L) LDR15 LDR22

R2..................LDR7 LDR6 LDR2 LDR9 RY2(R2) LDR11 LDR14 LDR11x LDR21

LEAD..............LDR4 LDR8 RY2(R1?L) LDR10 RY1(R2?L) LDR13 RY1(R2?L) LDR20

The LDR11x turn on in R2 mode shunt a portion signal with ground, because the signal level in R2 mode (as well as in LEAD mode) from tube V2A is much higher than in R1 mode?
And is there some relation between the LDR11 and LDR11x? Why one call 11 and other call 11x?
I hope I own a Mark IV, but I don't.
At last, thanks again!!!

hello Ironlung,

I sent you a PM with my email address because I'm interested in getting a soft copy of the power supply, the switching busses and the foot switch schematics. It would be great if you could oblige.

Thanks in advance Michel

It would be the wrong schematic for your amp. His is a MK IV B.

 

[michelj]

Thank you very much!!!!!
I got the whole schematic(including the power supply, the switching busses and the foot switch) and study it for a while. I don't understand "the second side of the trace" that you said, is there some more schematic about Mark IV?
I list the LDRs and Relays turn on in every mode, so is that right?

MODE.............Turn On(ON Resistance)

R1..................RY1(R1) LDR5 LDR12 RY2(R1?L) LDR15 LDR22

R2..................LDR7 LDR6 LDR2 LDR9 RY2(R2) LDR11 LDR14 LDR11x LDR21

LEAD..............LDR4 LDR8 RY2(R1?L) LDR10 RY1(R2?L) LDR13 RY1(R2?L) LDR20

The LDR11x turn on in R2 mode shunt a portion signal with ground, because the signal level in R2 mode (as well as in LEAD mode) from tube V2A is much higher than in R1 mode?
And is there some relation between the LDR11 and LDR11x? Why one call 11 and other call 11x?
I hope I own a Mark IV, but I don't.
At last, thanks again!!!

hello Ironlung,

I sent you a PM with my email address because I'm interested in getting a soft copy of the power supply, the switching busses and the foot switch schematics. It would be great if you could oblige.

Thanks in advance Michel

It would be the wrong schematic for your amp. His is a MK IV B.

Hello Boogiebabies,

I only realized after has a MK IV B. Heck I like the MK IV so much that I may eventually end up with more than one and who knows that might be the B version. I suspect the footswitch schematics must be somewhat similar. Have you got the switching matrix for the A?

Thanks Michel

 

[michelj]

hello Ironlung,

I sent you a PM with my email address because I'm interested in getting a soft copy of the power supply, the switching busses and the foot switch schematics. It would be great if you could oblige.

Thanks in advance Michel

It would be the wrong schematic for your amp. His is a MK IV B.

Hello Boogiebabies,

I only realized after has a MK IV B. Heck I like the MK IV so much that I may eventually end up with more than one and who knows that might be the B version. I suspect the footswitch schematics must be somewhat similar. Have you got the switching matrix for the A?

Thanks Michel

I was just taking a look at what I got from ironlung and the preamp and amp schematics are those of the MK IV A. That also seems to be the case for the other schematics.

Michel

 

[welshboogie]

Jeez BB, do you have a second brain to store all this info - I get problems just trying to figure out how to switch this **** MKIV on!!! :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:

 

[edge59]

Looking for a Mark IV B schematic. The powers supply and switching matrix is needed. Noise with the switching and a background static and some popping when switching with FT. SW. sound that comes and goes even after replacing tubes, any ideas? Switching manually is noisy and the loop light comes and goes, When I flip the standby switch, the light come back on, it is intermittent but the loop works fine. I cannot see any bad solder joints, but the SN74LS138N and DN7404N multiplexer and hex inverter chips are in question, maybe even q-10 2n5401, not sure about the 2n6426's. but the switching circuit appears to be problematic. It worked fine the last time I fired it up and it's been stored for months now, getting ready to either use it or sell it, but not like this. Anyone have ideas and or schematics for the IV B?
Thanks
Ed