[vmlistening]

I'm using an integrated PrimaLuna EVO 200 with Spatial Turbo speakers (open baffle). I have a mix of crackle and hum from the right channel. The TT, amp, CD player are all connected to the same power outlet source. The crackle and hum is from the right speaker only and it is intermittent without any pattern that I can notice. So the crackle and hum is not all the time.

What I've done without any luck:
I changed the speaker cables.
I swapped the speakers from left to right - crackle and hum is still from the right channel. So, it is not a speaker issue, I think.
I've unplugged the sub.

This seemed to have happened after one KT88 and auto bias fuse blew. Those were replace with a new fuse and EL34's

I'd appreciate any advice or tips or things to try out.
Thanks.

[FullRangeMan]

There is any resistor in the output tube?

[vmlistening]

I guess there is one in the EL34 tubes.
The PrimaLuna amp has an autobias. So I don't have to tinker with that.
I'm not sure if that's where you were going with this. My experience with tube amps is limited.

[FullRangeMan]

Sometimes when an output tube dies, it take along its resistor with it or it stay apparently good but becomes altered, the Prima Luna's Bias PCB also may be affected.

[vmlistening]

Thanks.
It could very well be that since this started to happen after a tube and auto bias fuse blew.

Are there things I could try to eliminate other factors that may be causing it?

[FullRangeMan]

Its an easy to test amp since there is plenty of space to access the components.

[vmlistening]

Thanks.
How would I know if the Bias PCB is shot - some resistor on it fried? 

I don't expect you to teach me how to fix this! I just want to be able to know if it is bad, and if there is an easy way to know that.

Thanks again!

[FullRangeMan]

Resistors and ICs may have been damaged or have their functioning altered, which seems to have been the case.

Unfortunately to trace this problem the amp has to be power on, which exposes you to high voltages that can stop your heart.

[FullRangeMan]

Thanks.
How would I know if the Bias PCB is shot - some resistor on it fried? 

I don't expect you to teach me how to fix this! I just want to be able to know if it is bad, and if there is an easy way to know that.

Thanks again!

In the image you can see each output tube has 2 resistors, after power off the amp and remove the power cord from wall and wait some hours to unload the capacitors check visually if they are not burnt or smoky, etc.

Additional tests will require a compliant meter and rubber shoes and rubber glovers among other security procedures. 

[Early B.]

"Crackle" sounds like a bad tube and they can be intermittent. Have you tried swapping left & right tubes to see if the crackle & hum moves to the left side?

[borism]

I agree with Early B that swapping L and R tubes would help identify a tube issue. In addition, if you haven't cleaned the tube sockets yet it may be worthwhile. You can do it by repeatedly unplugging and reseating the tubes. This should get rid of possible oxidation/dirt on pins and sockets.

[mick wolfe]

I agree with Early B that swapping L and R tubes would help identify a tube issue. In addition, if you haven't cleaned the tube sockets yet it may be worthwhile. You can do it by repeatedly unplugging and reseating the tubes. This should get rid of possible oxidation/dirt on pins and sockets.

Exactly. Proceed as mentioned above before digging any deeper into possible failed component ( resistor, etc.) issues.

[WGH]

I had the same problem with a Van Alstine preamp. I discovered NOS Mullards have copper pins which oxidized in a year, a quick and easy pin cleaning with CRC QD Electronic Cleaner fixed the noise problem.

[vmlistening]

Thanks. I swapped the #2 and #3 gain tubes on preamp section and so far there is no crackle/hum from any channel. I've only played it for an hour or so, though. I hope it stays that way!

[mick wolfe]

Good news. You've just done a basic tube socket/tube pin cleaning by simply reinserting the tubes. Next time the amp has been off for awhile and cooled down, use this same procedure on all of the tubes in the amp. (2 or 3 times per tube doesn't hurt) To take it a step further, lightly sand the tube pins with a fine sand paper and wipe the pins with isopropyl alcohol. When the alcohol has completely evaporated, reinsert.

[Tyson]

I do the light sanding and alcohol steps any time I swap in new tubes, too.

[mick wolfe]

I do the light sanding and alcohol steps any time I swap in new tubes, too.

 

[vmlistening]

Thanks.
Will do. I guess even the PrimaLuna will need some TLC!