#1
So my friends 6505+ has been making odd noises when he turns on the effects loop to use the pedals in that loop. It happens even if there are no pedals in the loop though so it's got to be something wrong with the amp.

I haven't really worked much with tube amps but I'm assuming there is a pre-amp tube that controls the effects loop isn't there? And if so; is it possible that this pre-amp tube is malfunctioning?

Eager to fix this!

-The amp works fine without effects loop on.
-It was bought used and just recently started doing this.
-It has never been re-tubed.

Let me know if you have more questions.
Rig:
Schecter Hellraiser FR
Peavey 6505 Head
Vader 4x12
BBE 482

DOD EQ
Boss NS-2
#2
change the tube out that works with the loop
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#3
Quote by selkies
change the tube out that works with the loop

Is it it alright to just throw a tube in there? I don't need to do any biasing like with power amp tubes?
Rig:
Schecter Hellraiser FR
Peavey 6505 Head
Vader 4x12
BBE 482

DOD EQ
Boss NS-2
#4
Not sure if the peavey has a tube bufferd fx loop or not...first thing u can do is try swpaing the pre amp tubes about a bit and see if that solves the prob
#5
Quote by Orethor
Not sure if the peavey has a tube bufferd fx loop or not...first thing u can do is try swpaing the pre amp tubes about a bit and see if that solves the prob

preamp listing
Here's a post that shows that pre-amp tube v3 is the effects loop buffer tube.


So if I just pull out the v3 and put in a different tube; assuming that the tube is the problem, then the problem should be fixed? Or I can start troubleshooting different problems at least.
Rig:
Schecter Hellraiser FR
Peavey 6505 Head
Vader 4x12
BBE 482

DOD EQ
Boss NS-2
#6
Try swappin it with any tube except V4 then and see if it works better...then ull know...
#7
preamp tubes dont need biasing
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#8
Quote by Orethor
Try swappin it with any tube except V4 then and see if it works better...then ull know...

I have spare pre-amp tubes from when I re-tubed my 6505 so I'll just stick one of those in.

Thanks for the help guys!
Rig:
Schecter Hellraiser FR
Peavey 6505 Head
Vader 4x12
BBE 482

DOD EQ
Boss NS-2
#9
Could be dirty contact in the jacks? Put a bit of contact cleaner on the end of the lead and run it in and out a few times, pretty common problem with the 5150/6505.

But it does sound more like a microphonic preamp tube. strange it only plays up with the effects loop
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Gibson Explorer New Century
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Amps:

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Marshall JCM800 2203 - 1960A

Pedals:

Crybaby 535Q
Rockbox Boiling Point Overdrive
#10
The 6505+ is a fixed bias anyway.
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#11
Quote by Yngwi3
The 6505+ is a fixed bias anyway.


Yeah I'd recommend any 6505/5150 owner to get an adjustable bias installed by FJA mods. It's such nice thing to have.
#12
So just to update; switched out the v3 tube for an older one and seems to be working properly now. Not sure if it was a bad tube or just dirty contacts; but if it works why fix it.

Thanks guys!
Rig:
Schecter Hellraiser FR
Peavey 6505 Head
Vader 4x12
BBE 482

DOD EQ
Boss NS-2