The tall black barrels are the high voltage filter capacitors in a tube guitar amplifier, or a "valve amplifier". The top of the viewable metal can with the "crease lines" that's surrounded by a brown plastic Mylar "glove" are still flat. There is pressure behind this glove that feels about like a volleyball causing it to bulge, which is caused by the over heated gel/liquid electrolyte turning into gas!
These are low grade filter caps used in almost all mass produced musical instrument amps made over seas, beginning around 1990. This amp is a stock Pignose B100V Bass tube guitar amplifier built around 2003, with about 500 volts on the power tubes. These caps are starting to fail, and are beginning to "leak" excessive voltage through the cap to ground, which creates heat which accelerates this dangerous degradation that can damge the amp. They may survive another 100 hours total of heavy operation, but that's pushing it - this leads to less output, the fuse blowing repeatedly, and the possibility of power transformer damage. Also the amp will hum more in general and will get real loud hum when trying to amplify a loud guitar signal, which sounds sort of "buzzy", because it is at twice the frequency of the 60 cycle A.C. mains power i.e. 120 HZ.
Here is a top view of the underside of chassis in original factory condition,
I suggested using highest quality capacitors within reason, at least in the first stage of filtering which supplies 80% of the high voltage power needed, which is for the power tubes. Many pro amp builders and bench techs consider real American Sprague "Made in U.S.A." caps to be some of the best and I agree, so that's what we used - the orange ones on the right side of the power supply PC board in the next image below.
For the remainder of the filter caps, we used decent quality Nichicon caps made in Japan, mostly because they are smaller and would fit on the board better. They also cost about a third of the price of the Spragues, but are only handling 20% of the power as the Spragues in this circuit, so it is not critical.
For the capacitors to handle the voltage of the first 2 stages, we used a pair in series, or what's commonly called a "totem pole" to handle double of their rated voltage. The orange Spragues will be forgiving of 20% excess voltage, the Nichicon and most other imports caps will only handle up to their rated voltage! The voltage on the first stage is about 500 volts, about 485 V on the 2nd stage, and initially when turned on it will surge up close to 600 volts DC. With a pro cap job and a few other minor enhancements this becomes a world class professional bass amplifier. This amp delivers 100 tube watts using 4 - 6L6 tubes, rivaling in tone what many players and studios consider the best sounding tube bass amp of all time - the Ampeg B-15N which delivers 35 watts, using 2 - 7027 power tubes.
We added more filtering, for a total of 75uf at 600 working volts