learning, building and testing tube amp

[fragman56]

Hum again??

I just hooked up my SE 6bq5 in the chassis (new layout compared with the breadboard) and got a lot of hum.

Quick question: Does it matter where the PS filter caps are grounded? I have a 10mf, 420 mf and 80 mf in a CRCRC config with the C's grounded at various points in the circuit. Could this cause humming problems?

FWIW, I am using the same PS system as in the breadboarded version.

Thanks in advance,
Rick

 

[Joel]

Rick, 420MF is a big cap. Too big for a tube PSU. Lower it to 100uF.

Also, if you are using the same PSU, and it nows hums, where it did not before - then it has to do with wire or transformer placement - not where B- is. Ground is ground.

 

[fragman56]

two simple questions

1.What exactly is a "ground loop"?

2. What is the function of a series resistor in the control grid of a tube (grid stopper?)?

Thanks,
Rick

 

[fdegrove]

QQ

Hi,

1.What exactly is a "ground loop"?

Since I don't have a short answer for that:

GROUNDING MATTERS

2. What is the function of a series resistor in the control grid of a tube (grid stopper?)?

It helps to prevent HF oscillation.
Some people tend to build oscillators...for audio use.

On a more serious not, some tubes and circuit topologies are more prone to it than others.

In SS equipment these are called gatestoppers.

Cheers,