Illinois capacitors

[Chuck H]

What failure mode are we talking about? I could be mistaken, but seem to recall Chuck talking about the number of phase inversions on the preamp supply node, and thus the HR series having the issue of howling when the preamp filters (decouplers) stop decoupling, where other amps don't exhibit the same symptom and it goes unnoticed?
Chuck H ?

BING BING BING BING BING!!!!

That's the ticket exactly. I haven't examined them all, but the ones that have come up for discussion here WRT oscillation issues related to filter failure do indeed have like phase gain stages on the same filter node... And IC caps. So...

Some of this could come down to design. I have to admit that there is no research to discount that another brand of cap wouldn't exhibit the same short-ish term problems in those amp models with some small rise in ESR due to age. So there's that.

But I do have a little experience with IC caps and I would never use them in anything I build. Does that mean they're sub par? Maybe not. But it does mean that I, and clearly many others have reason to suspect they are. Whether there are indisputable numbers in print or reasonable arguments THAT is enough for me to avoid them. Even call them out as candidates for replacement when they're over ten years old. Maybe they're lack of quality can't be proven by the available print, but it can't be disproven either and it's strongly inferred!!! Why stick our heads in the sand?

[DFuller]

What failure mode are we talking about? I could be mistaken, but seem to recall Chuck talking about the number of phase inversions on the preamp supply node, and thus the HR series having the issue of howling when the preamp filters (decouplers) stop decoupling, where other amps don't exhibit the same symptom and it goes unnoticed?
Chuck H ?

More often than not just 120Hz hum (as opposed to the 60hz hum, which comes from the heater hum balance resistors burning themselves out...), but yes - sometimes howling! In fact, on one of the Peaveys, the problem presented itself as motorboating only when there was significant current draw on the power tubes. Was a bizarre issue, to say the least.