Fender Blues Deluxe Reissue clean channel Noise.

[seeemilyplay]

Hello folks,

I have a BDR amp with noise problem. Not hum and hiss. A lot like pop sound.
There are some tests I have made:

1. The pop sound is not always heard. Sometimes it happened in 10 or 15 mins.
But sometimes it happened just at turning off the standby. Sometimes the noise will gone itself.
2. The pop sound happened only in the clean channel. The noise stopped after switching the drive channel.
3. The noise won't gain by increasing amp volume knob. But the noise level will decrease by turn the treble knob down. The noise seems happened with/without signal input.
4. The preamp tubes (V1, V2, V3) have swap to new ones. The noise still happened.
5. When the pop sound happened, I insert the guitar cable plug to the return jack. The noise is gone.
The amp sounds good.
6. Use stick knock the tubes or PCB units, Nothing happened. The connect wire is good.

After reading the schematic, I guess It's a relay problem. After installing new relay K1, K2 , The noise is still.
I also replace the new cap C33, C35, C36. Nothing better.
I use oscilloscope see the waveform. When the noise happen. The waveform after C53 is getting little distortion. But I don't know where is the problem.




Hope someone can give me some advice. Thank you.

SeeEmilyPlay

[g1]

When you switch to the drive channel, do you have the master turned all the way up? If not, you may not notice the noise and it may actually be on both channels.

[dwmorrin]

I would suspect R4, the 100k 1/2W plate resistor, or possibly the next plate resistor, R11.
The wires to and from the tube sockets often need to be resoldered on these amps. Could be a connection that is "passing" the chop stick test, but is really not good.

[seeemilyplay]

Hi, G-one : No, I don't try to turn the master level of the overdrive channel to max. I miss the test. I'll try again. Thank you.

dwmorrin : This amp has repaired by someone before. All connect wires and units have been resoldered. You're right maybe I need to check all the soldered point all over again.
I guess the noise comes from the preamp stage (V1, V2). Because the EQ can roll off the noise. Is it right?
Is any possible the problem in the Relay circuit? Thank you.

[dwmorrin]

I guess the noise comes from the preamp stage (V1, V2). Because the EQ can roll off the noise. Is it right?
Is any possible the problem in the Relay circuit? Thank you.

My first guess for popping noise is a noisy plate resistor. For V1, and V2, those are R4 and R11.
In your first post, you said you replaced the relay. I would not suspect the relay after that.