Plexi Crackling

assquatch20

Active Member
Joined
Jan 19, 2019
Messages
122
Reaction score
238
Location
Tennessee
I guess I need to get some de-oxit and go through it but any ideas where to start or alternative theories? It seems to be when it's turned up with the certain notes on the low E. Turning down channel 1 when I jumper the channels or just plugging into the second channel seems to make it less noticeable but it's still there. Only seems to happen when turned up a bit and hitting some low notes.

It did this with a different guitar, cab, cables and such as well. Had a look at the tubes when it did it and could see no arcing or anything strange but I'm not a real amp tech.

Any help is appreciated.
 
Last edited:

Gene Ballzz

Well-Known Member
Joined
Feb 19, 2013
Messages
3,816
Reaction score
4,606
Location
Las Vegas, NV
@assquatch20

Remove and reseat the pramp tubes, especially the first one! Do not use DeOxit D5 on the tube sockets, but instead an electronic cleaner that does not leave any residue or lubricant, such as CRC QD Electronic Cleaner, if using any cleaner!
Let Us Know?
Gene
 

assquatch20

Active Member
Joined
Jan 19, 2019
Messages
122
Reaction score
238
Location
Tennessee
@assquatch20

Remove and reseat the pramp tubes, especially the first one! Do not use DeOxit D5 on the tube sockets, but instead an electronic cleaner that does not leave any residue or lubricant, such as CRC QD Electronic Cleaner, if using any cleaner!
Let Us Know?
Gene

Hey thank you for the advice. I actually have some of that CRC QD stuff here I may try. I tried some different preamp tubes with no luck. I noticed it's on both channels so I edited my post a bit.

Where would you start spraying?
 

Gene Ballzz

Well-Known Member
Joined
Feb 19, 2013
Messages
3,816
Reaction score
4,606
Location
Las Vegas, NV
Typically, I would spray the pins of the tube and then work it in/out a few times while still wet! Alternatively, you could spray the non-residue cleaner into the socket's grippers and work a tube, in/out in the same manner! The second method may "flush out" debris, but might get a little messier, although a good non-residue cleaner will leave little trace of it's own!
Just My Way,
Gene
 

assquatch20

Active Member
Joined
Jan 19, 2019
Messages
122
Reaction score
238
Location
Tennessee
A Plexi? Not much to go on.

Well it's a 1976 model 1959 SLP 100w. Not labeled as a MKII though.

I cleaned the tube sockets and tried different preamp tubes to no avail. I have a feeling it's something simple but can't really tear into it just yet.
 

Matthews Guitars

Well-Known Member
Joined
Aug 17, 2019
Messages
6,659
Reaction score
10,903
Has it ever had a cap job done? That can be a clear symptom of them being due.
 

Matthews Guitars

Well-Known Member
Joined
Aug 17, 2019
Messages
6,659
Reaction score
10,903
Then it's PROBABLY not the caps. Wiggle the tubes in their sockets. If it's a crunchy socket, you'll know it.
 

Chris-in-LA

Well-Known Member
Joined
Jul 19, 2018
Messages
3,398
Reaction score
3,525
Location
Los Angeles
Might also be a cold solder joint. Try poking around inside with a wooden chopstick if you are comfortable working with high voltages.
 

neikeel

Well-Known Member
Joined
Feb 12, 2014
Messages
7,339
Reaction score
7,032
Most commonly resonant frequency causing intermittent connection ie dry joint. Occasionally internal failure of a resistor- often thermally induced too.
I’d check wiring esp mods and recap connections, particularly if RoHS solder used.
 

assquatch20

Active Member
Joined
Jan 19, 2019
Messages
122
Reaction score
238
Location
Tennessee
Most commonly resonant frequency causing intermittent connection ie dry joint. Occasionally internal failure of a resistor- often thermally induced too.
I’d check wiring esp mods and recap connections, particularly if RoHS solder used.
Those are the two most likely culprits to me at this point but not sure yet. I may take it to someone or I may drain the caps myself and have a look. It's not my top priority right now but it'll get done.
 

Chris-in-LA

Well-Known Member
Joined
Jul 19, 2018
Messages
3,398
Reaction score
3,525
Location
Los Angeles
If you use a chopstick, the amp must be running, no sense draining the caps. Tap or touch every connection and component you see especially around where the mods were done. It also helps if you have a magnifying glass.
 


Top