Question about signal chain

[RDK]

Studying tube amps. About to build first one. I was curious. The signal circuitry and power amp circuitry. What keeps high voltage from getting into the signal chain and into the guitar. Are the 2 chains separated by a tube? May seem like a silly question but I'm going to ask anything I can think of before this build. Ha

[big_teee]

Coupling Capacitors.
On the first stage the signal is amplified and ends up on the plate voltage.
You connect a coupling capacitor to the plate.
The B+ is stopped, but the signal crosses the coupling cap.
Simple but effective.
T

[RDK]

Coupling Capacitors.
On the first stage the signal is amplified and ends up on the plate voltage.
You connect a coupling capacitor to the plate.
The B+ is stopped, but the signal crosses the coupling cap.
Simple but effective.
T

Oh ok. Coupling capacitors block DC voltage all together correct? So you have coupling capacitors in line between your guitar signal and the DC voltage.

[big_teee]

Yes, you got it.
Have a look at this Schematic.
It has the Voltages on it.
If you look, anytime they leave the high voltage with signal they put a Coupling Cap.
Start at V1 and follow the signal through toward the Power section and you will see the Coupling Caps.
Most are .022uf.
Good Luck,
Terry
JCM800_2204Schematic.pdf
**
22nf and .022uf are the same.

[g1]

If you are asking what keeps the high voltage out of the the guitar itself, the grid (input) of the first preamp tube does not have high voltage on it.

[Steve Conner]

Yup, and the grid is just a little metal grill dangling inside the evacuated tube. It has no physical connection to any of the other electrodes. Behold the magic of tubes.

If you did something really stupid, like pulverizing the first preamp tube with a hammer, or replacing it with a pickled onion, you could probably get high voltage to feed back into the guitar input.

But all of the metalwork on your guitar is supposed to be grounded to the amp's chassis, which in turn is grounded to the green wire of the mains supply. The high voltage would just appear on some wires inside the control cavity.

It is possible to get electrocuted by your guitar. The classic way is for the amp's chassis to get connected to the hot wire of the mains supply, either by bad wiring at the gig, or a faulty "death cap" (another story in itself)

[Jazz P Bass]

[QUOTE=Steve Conner;252905]
If you did something really stupid, like pulverizing the first preamp tube with a hammer, or replacing it with a pickled onion, QUOTE]
A 'pickled onion?'
Now , that would be stupid

[Enzo]

Olive my amps have that.