Tube Amp Troubleshooting Question

[BoogieMKIIA]

I bought a used Vox Night Train 15 NT G2 several weeks ago. Sounded great in the store and the few times I played it at home. I pulled it out today to check how it does with my pedal board and heard a buzz/grit as chords and notes decayed. Some pulsing in the tails. It gets loud and the initial tone sounds good. I have tried the following so far to no avail.

• swapped speaker cable
  
• guitar direct to amp, no pedals
  
• different speaker
  
• different guitar
  
• changed all preamp and power tubes
  
• have not tried a different guitar cable, will do that.
  

Before I open it up and start probing, does anyone have experience with similar symptoms? Any suggestions?

 

[Saul Goodman]

I had to use Doxit (I think that's how you spell it) on my NT tube sockets. I sprayed the pins of the tubes and pressed them in and out of the socket not quite pulling it out all the way and being careful not to bend the pins. That would be the starting point and about all the qualifications I have to work on an amp. Perhaps @Dutchmanor @butcher can chime in.

 

[BoogieMKIIA]

I had to use Doxit (I think that's how you spell it) on my NT tube sockets. I sprayed the pins of the tubes and pressed them in and out of the socket not quite pulling it out all the way and being careful not to bend the pins. That would be the starting point and about all the qualifications I have to work on an amp. Perhaps @Dutchmanor @butcher can chime in.

Thanks. All the sockets are really tight, but it’s an easy thing to try and good practice for older tube amps. I also have the FX loop jacks to check out, could be oxidized. I opened the chassis when I got it, everything still looks new but it it’s over 10 years old. It was repaired in 2019 but the place that did the work doesn’t recall the details. The repair code indicated it was only a bench charge so nothing big at that time.

i found the service manual online so I won’t be going in blind if it comes to that.

 

[Saul Goodman]

Thanks. All the sockets are really tight, but it’s an easy thing to try and good practice for older tube amps. I also have the FX loop jacks to check out, could be oxidized. I opened the chassis when I got it, everything still looks new but it it’s over 10 years old. It was repaired in 2019 but the place that did the work doesn’t recall the details. The repair code indicated it was only a bench charge so nothing big at that time.

i found the service manual online so I won’t be going in blind if it comes to that.

Speaking of the FX loop, you can take a short patch cable and jumper between the send and return and see if there is any change.

 

[BoogieMKIIA]

I may have figured it out but my method missed a step. Today I worked a 1/4” plug in and out of the FX send and return jacks, then turned the amp on to test. The weird sounds underneath the notes are gone. However, I did not check before I worked the jacks. My daughter has a migraine today so I will check later when I can turn it up more. I did play it awhile in all modes and with my pedal board and it seems OK.

Before I buttoned it up, I did the Deoxit on all tube sockets and all input and output jacks - spray some on the pins and plug, seat/reseat a few times. All appears working OK. We play a party this Friday and I will give it a shakedown cruise. With the Quilter US Superblock as backup.

I had to work the input jacks on my Marshall after a long time not being played. Was picking up AM radio, weird.