Why does my express sound like FUZZ?

[fugezii]

For the noise problem can't be solved, I rebuilt one.and I checked the layout 3 times with highlighter. can't connection errors were found. The voltage data was measured and only V2 Pin1 appeared to be slightly above normal. Connected to the guitar, the volume at 12 o'clock can hear a faint sound. Like fuzz! Is it a problem with any damaged tube or potentiometer?
who can save me, is about to collapse!

[martin manning]

What are pin 3 voltages on V1a and V2a? Looks like V2a has a problem though... bad solder joint, wrong value resistor, bad tube or socket connection, etc.

[pdf64]

What happens to the V2 plate voltage if its grid leak resistor is shorted out (linked to 0V common)?

[wpaulvogel]

Probably nothing to the plate voltage, but it won’t amplify signal because signal is shunted to ground. What is your cathode voltage on V2?

[fugezii]

Probably nothing to the plate voltage, but it won’t amplify signal because signal is shunted to ground. What is your cathode voltage on V2?

What are pin 3 voltages on V1a and V2a? Looks like V2a has a problem though... bad solder joint, wrong value resistor, bad tube or socket connection, etc.

What happens to the V2 plate voltage if its grid leak resistor is shorted out (linked to 0V common)?

Hi, guys
Sorry for the late reply. I measured them again today. As you can see, the voltage on V2 PIN3 is also abnormal, it is much higher.

[martin manning]

Same diagnosis. There is no current flowing through V2a. Note that the plate voltage is the same as the supply voltage.

[fugezii]

Same diagnosis. There is no current flowing through V2a. Note that the plate voltage is the same as the supply voltage.

I see! Now I think it is 100k resistance damage or poor contact, I will try to replace it and feedback the result, thank you so much！

[pdf64]

If there's no current flowing through V2a, how can there be cathode voltage, nevermind that it's somewhat high?
Perhaps the 100k plate resistor is wonky, eg really 100 ohms?

[wpaulvogel]

What is the cathode voltage on v2. If there is some picture or image it won’t open. All I see is a little box with “image “ inside.

[wpaulvogel]

if the cathode is "open circuit" the voltages will be supply at the plate and somewhat lower at the cathode.

[fugezii]

What is the cathode voltage on v2. If there is some picture or image it won’t open. All I see is a little box with “image “ inside.

V2 pin3 gets 5.6v

[wpaulvogel]

Well with that voltage you are in cutoff. Are you 100% sure that you have a 10k resistor on pin 3? You should have about 2.8-3 volts.

[fugezii]

If there's no current flowing through V2a, how can there be cathode voltage, nevermind that it's somewhat high?
Perhaps the 100k plate resistor is wonky, eg really 100 ohms?

Well with that voltage you are in cutoff. Are you 100% sure that you have a 10k resistor on pin 3? You should have about 2.8-3 volts.

Hey guys! It get work!
I changed 150K, 10K, 100K; 0.0022UF & 0.1UF (measurement is not damaged)
and the 10K grounding part was re-welded,
Now everything is normal .
V2 pin1= 275v; pin3= 2.8v
Maybe it’s god damn 10k grounding problem!
Thanks for everyone's help. This frees me from the pain. You are great!

[fugezii]

If there's no current flowing through V2a, how can there be cathode voltage, nevermind that it's somewhat high?
Perhaps the 100k plate resistor is wonky, eg really 100 ohms?

Well with that voltage you are in cutoff. Are you 100% sure that you have a 10k resistor on pin 3? You should have about 2.8-3 volts.

Hey guys! It get work!
I changed 150K, 10K, 100K; 0.0022UF & 0.1UF (measurement is not damaged)
and the 10K grounding part was re-welded,
Now everything is normal .
V2 pin1= 275v; pin3= 2.8v
Maybe it’s god damn 10k grounding problem!
Thanks for everyone's help. This frees me from the pain. You are great!

[wpaulvogel]

I’m guessing that it screams now! I love these amps.