Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ALBATROS1234 on February 14, 2018, 06:14:34 am

Title: Grid stopper or coupling cap?
Post by: ALBATROS1234 on February 14, 2018, 06:14:34 am

Normally I use a .01 cap with a 1 meg grid leak on my inputs but noticed many times there is a grid stopper resistor instead of a cap. On fenders it's usually a 68k. Yesterday upon suggestion to solve a problem I used a grid stopper and it helped somewhat. So my question is  grid stopper or cap or both? What are advantages of on the other or both?

Title: Re: Grid stopper or coupling cap?
Post by: sluckey on February 14, 2018, 06:24:35 am

Grid stopper resistor on the input is used to hopefully eliminate RFI. Coupling caps are rarely used at the input unless you have an old fashioned grid leak biased circuit, in which case, the cap is a must have item.

Title: Re: Grid stopper or coupling cap?
Post by: jojokeo on February 14, 2018, 02:02:48 pm

A cap on the input can be used for several things such as insurance against DC making it's way through from on board preamp inside your guitar/active pickups, wireless transmitters, an issue arriving from a pedal board, certain VVR circuitry, etc. Another could be if you were trying to limit low end response for a particular reason?
There is another way around RFI interference which places a small cap with short lead going from input ground to chassis.