intermittent fault with 102 ODS

[norburybrook]

Hi,

I recently persuaded my friend to purchase a lovely 102 50w ODS combo built by a forum member.

Sod's Law has come into play and within a couple of days of touring it started to male a crackling distortion noise, fortunately the crew swapped the amp out mid set. THis happened one more time a few days later then has been fine for the last 7 gigs.

Last night however it happened again. The sound is almost like digital clipping or clipping a solid state input and just seems to appear out of the blue.

The guitarist is playing an active Eric Clapton custom shop strat.


Any ideas as to what to check or what it might be? I'm going to swap out the valves today as a first thing to try as I'm going to sound check early.

TIA


Marcus

[martin manning]

Is anything plugged into the loop jacks? If not the signal must pass through the switching contacts, which could be the cause of the the problem.

[norburybrook]

Thanks Martin, house would I check that? Would putting something in the loop bypass those switches and eliminate the problem?


Marcus

[rock_mumbles]

Plug a patch cable into the fx loop in/out

[David Root]

Very good chance this is indeed the problem.

I have had exactly that happen in one of my builds. I changed the jacks from standard grade Switchcraft to MilSpec grade (P/N C12AX) and that solved it. The milspec has better nodular silver plated contacts on the the shorting pin and the +ve pin and is US made, not C***A. I also use milspec on the input and main output jacks too for the same reason. Costs more but worth it.

Could also be a dry joint on one of the pot grounds, I had that happen too.

[norburybrook]

Thanks guys.

Got to love this forum 😊

Marcus

[norburybrook]

Well it wasn't the sockets amp started playing up end of the first set again e even with a jumper lead in the send/return.


Which valves would you try swapping first if you think it might be valves?

Marcus

[martin manning]

Any chance you can make a recording of the distortion you are hearing?

[hitchcaster]

sounds like guitar.... you swapped guitars and it still did it?

[norburybrook]

Any chance you can make a recording of the distortion you are hearing?

It's very intermittent and has only happened mid set, so the crew have to change amp quickly when it happens .

I changed the 3 ax7 valves yesterday and so far it's worked 100% for the last 2 gigs.

However it did 5 gigs on the trot last week without issue.

Fingers crossed we've got it


Marcus

[martin manning]

I guess you'll just have to wait and see. Sound cutting out sounds like an intermittent open, which could be a bad solder joint or socket-pin connection; or possibly a signal short to ground, which could be something like a whisker of shield braid on one of the coax runs grounding the center conductor.

[norburybrook]

Tour finished

Just thought I'd report back on this to say it was indeed one of the 3 x 12AX7 valves, however I'm not sure which one as I just swapped all 3. My feeling it is the phase inverter valve as that was a NOS and V1 and V2 were new JJ's


Anyway just to say thanks for the suggestions and for the future, I now know crackly intermittent noises can be valve problems.

Marcus

[Structo]

Tube amps take a lot of abuse when on tour.

Vibration and bumpy roads can raise havoc on the tubes.

Not to mention the load out and load in handling.

Not sure if you use flight cases for your gear but that can get expensive as well.