Crackling

[Old Fart]

Amp is crackling. Not when the knobs are turned. The crackling happens when notes are played. Doesn't happen all the time, but often enough. It's not the bass, and it's not the speaker. It's the amp. It is subtle, but it's there. Sometimes. Crackling when a tone is being sent through the amp and speakers. The amp is an SVT. Magnavox-era.

Any clues?

[fdeck]

I once traced crackling to a bad cable -- after I got my amp apart.

[B-string]

Most likely the 6C4 in the preamp. Try moving the amp off the cab to isolate the head (and tubes) from cab vibrations.

[Old Fart]

Ah Hah! This must be what is meant by a tube being "microphonic."

I will isolate the head from the cabinet vibrations and see if the crackling goes away. Thank you.

[dincz]

Originally Posted by Old Fart

Ah Hah! This must be what is meant by a tube being "microphonic."

I will isolate the head from the cabinet vibrations and see if the crackling goes away. Thank you.

Microphonic tubes don't so much crackle as behave like microphones - meaning if you tap the amp, you'll hear a sound from the speaker. It's often a ringing sound.

[B-string]

Originally Posted by dincz

Microphonic tubes don't so much crackle as behave like microphones - meaning if you tap the amp, you'll hear a sound from the speaker. It's often a ringing sound.

This is very true. I also have had multiple cases of 6C4's popping, crackling, hum and an odd jingling sound (best appreciated in December)