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]

2 hours ago, Saul Goodman said:

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]

1 hour ago, BoogieMKIIA said:

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.