what does this Diode network do exactly?

[Phorhas]

I saw this diode network- two diode shunting to ground on each side and a diode connecting them in the middle - on several FX (V-Twin 4 example) and I wonder what does this do exactly? what's the purpose for the the diode in the middle?

http://www.tubefreak.com/V-Twinp.gif

[RobB]

Doides D1 to D5 give you a clipping threshold of six diodes (three each way) for the price of 5.  If you follow a conventional current from the signal line to earth you will have pass through 3 diodes.  If you follow a conventional current from earth to the signal line, again you will have pass through 3 diodes.  3 * 0.7 = 2.1 volts either way.  

The same thing could be achieved using three in a row each way (six diodes).  

The Marshall JMP1 has the same arrangement. Compactness and lower parts count.

[Phorhas]

is that all?

does MESA find it too expensive or complicated to use the regular 3-in-a-row setup?

[smoguzbenjamin]

Maybe it's also cause it looks fancy :mrgreen: Plus, saving 20 ccents once isn't much, but saving 20 cents over 5000 times is gonna be a lot more. $1000 to be precise, and I'm sure MESA makes more than 5000 amps a year

[RobB]

Two components (bridge rectifier + diode) to be placed instead of 6 may also save time on the production line.

[Alex C]

Above the diodes in the schematic it says "4x1N4148."  It doesn't specify what type the fifth should be, and I can't imagine that it would matter.  Is this a misprint or am I missing something?

Alex

[Paul Perry (Frostwave)]

Above the diodes in the schematic it says "4x1N4148."  It doesn't specify what type the fifth should be, and I can't imagine that it would matter.  Is this a misprint or am I missing something?
Alex

Interestingly, it sometimes DOES matter what the 5th diode is. Imagine what happens if it is a zener, for ezample, and the diode ring is arranged so that it is reversed against the others. Then you get a circuit that conducts as though it is a symmetric zener. And so on. And if it is Ge, then it looks as though there are parallel Ge diodes there (with each having 2 1N4148s in series). Not that this is what is happening here AFAIK, buyt it is a useful circuit trick.