Fluttery/rumbly/rubber bandy type sound on JTM50

[the boogie man]

Interesting, do you think it could just be beat frequency?

[rgorke]

Interesting, do you think it could just be beat frequency?

I thought of that except if I plug the guitar directly into another amp it isn't there.

[rgorke]

Ok, here's picture.

Board is a repurposed board and lifted off of its stands so I could poke underneath with a chop stick.

Wires may appear to be all over the place, that is because I have been moving them to see what if anything helps.

I had the OT secondaries shrink wrapped together but have now started to pull them apart.

I did install new 50+50uf filter caps. Seemed to help some but not perfect.

[shakti]

Now, I'll be polite and say that I have seen tidier builds. However, clean layout and shiny new components with straight leads does not guarantee good sound. Nevertheless, there are so many Places where there *could* be a dodgy solder joint or less-than-Perfect Connection or layout.

IIRC you said you have reflowed every solder joint? I think I would go one further and clean all tube sockets of solder, then make a new stripped end for each wire to ensure good, clean contact. As with my own amp, no particular part jumps out as being the obvious one to troubleshoot. But in my case, it turned out to be a set of tone stack pots with less than ideal values, possibly a dodgy solder joint or layout around V2 or V3.

BTW, I think we forgot to ask, but does this sound happen on both channels?

[Tazin]

Aside from some obvious issues (i.e. bit messy board, and needed shortening of the mixer cap leads), possibly try changing the two 100K plate resistors for V1 with some carbon film resistors. The carbon composition resistors are not the best for this location...Tend to be noisy.

[coldengray]

Yikes - messy build. Issue could be anywhere.

[rgorke]

Yeah, I know it is a mutt. The board was repurposed. The amp sounded fantastic for nearly 2 years prior to this issue. Something went bad....

The V1 plate resistors originally were 100k Iskras and have been switched out 2 times between these CC and CF...nearly the entire amp was Iska CF resistors and mustards.

It isn't a "noise" per se like a grounding hum. It is some sort of oscillation in the sustain on the notes.

It happens with all inputs regardless of which I use.

I did switch out the tone pots one at a time. The treble pot switch seems to have really improved things.

I also looked under the board and saw a big solder booger at the 1M grid resistor....

Thanks for the input...I may redo the board at some point soon.

[rgorke]

I think I am getting this straightened out. Previously I had the OT primaries twisted together. This is how most, if not all, the amp instructions say to do them. I now have each of the primaries going to opposite sides of V4 and V5 rather than in between them.

I also hard wired the 16 ohm tap to the output Jack to make sure the switch wasn't an issue.

The buzz distortion is mostly gone with the OT primaries way apart. Not sure why this is helping. Something tells me something might not be 100% correct with the OT.

That being said, the tone is actually pretty good.