Marshall 2210 Reverb Recovery

[lowell]

Anyone notice there's no grid leak on the recovery for the reverb? I had this thing apart on the bench and it's humming like crazy. Started pulling tubes and noticed this tube was really hot. Please correct me if I'm wrong, but this seems like a huge design flaw. The designer is depending on the tank's output coil to ALWAYS be in circuit AND to be functional. We all know those little wires to the coils break quite often and easily. So, I'm gonna add a 100k for reassurance. 100k because the coil dc resistance is 200ohms. 1meg seems a bit much, and too low may interact too much. I guess using the x10 rule, a 2k would work... but can't hurt.

http://www.drtube.com/schematics/marshall/2210prem.gif

[Enzo]

Ah, but there is a grid return resistor - the reverb pan transducer itself. Yes, they designed the amp for to be a working amp. Just as your car was designed and built for there to be air in all the tires all the time. There is no air leak resistor so to speak inside the tires. Just like a bad tube is to be fixed, a bad reverb pan is to be replaced.

The circuit could use a 1 meg resistor or some such from grid to ground for when no pan is connected. But once the pan is in place, that 1 meg will have the 200 ohms of the pan DC resistance, and the 2200 ohm impedance of the same, which pretty much makes the 1 meg invisible. You are right, you don;t want a lower value resistor loading the transducer.

[lowell]

Yes I realize the transducer is acting as grid leak. I just don't see why the cost of ONE resistor outweighs the cost of replacing a red plating 12ax7. Not sure how tires are designed or I'd invent something to fix flats too.

[Enzo]

They already have "run flat" tires. Some are used as spares, some in critical applications where a flat tire would endanger the occupant if the vehicle had to stop.