CE 4x20 Can Cap failed for second time

[sonicmojo]

I have this '67 Blackface Princeton Reverb back on my my bench a year after I replaced a very new looking 4x20 475V CE can cap that had failed with another same brand new CE can cap. Is there anything I can consider that could be causing early failure of the can caps or is this amp just lucky? Voltage in the amp does not appear to exceed about 400-410V.

Edit: the first cap I replaced was a 2004, the replacement cap I need to replace again is a 2016. The first cap had failed on 2 nodes. This second cap has failure on 3 nodes. I am hesitant to replace again before I consider other things......

[tubeswell]

What do the HT voltages look like with the amp on standby?

[sonicmojo]

What do the HT voltages look like with the amp on standby?

This is a fairly stock circuit Princeton Reverb so doesn't have a standby switch. It does have replacement transformers but they seem to be right. It has a 5U4 rectifier tube.

[pdf64]

The HT Vdc will shoot up about 10 seconds after power up, as the 5U4 with its heater cathode warms up to operating temp quickly.
The HT will then start to come down after about another 30 to 60 seconds, as the other tubes heat up.
What is the highest Vdc each HT cap section is exposed to, and for how long, during the above period?
Vintage can caps often used to have a 'surge' voltage rating noted on them, usually about 50V higher than the normal 'max continuous operating' Vdc rating.

[Stevem]

I have done CE's can's in many amp's and most recently two came back.
In 2007 in two mono block Heathkit amps and in one it had to be replaced in 2016" and in the other just this Summer.

I think the company (CE) changed owners at some point , but when and if things are better or worse it's hard to say!

One thing is for sure of any amp that has been recapped, that being if the owner only plays it and or uses it once every 4 months then you can count on the Cap's life being near 25% less then what it could be!

[Lauri]

Some of those CE Mfg can caps only have a 55°C temperature rating. I wouldn't expect it to last very long in a tube amp. Was the can cap you used rated for 85 or 55°C?

[sonicmojo]

Some of those CE Mfg can caps only have a 55°C temperature rating. I wouldn't expect it to last very long in a tube amp. Was the can cap you used rated for 85 or 55°C?

Interesting. The first one is marked 85C, the second one is marked 65C. The replacement I have on hand is also 65C and it looks like the new ones you can order are all only 55C. I'll ask the customer what conditions he plays in and may reconsider what to use. There is a CE 20/20/20/10 450V available to order that is 85C but may require a clamp or bigger hole.

[tubeswell]

What do the HT voltages look like with the amp on standby?

This is a fairly stock circuit Princeton Reverb so doesn't have a standby switch. It does have replacement transformers but they seem to be right. It has a 5U4 rectifier tube.

In that case, its likely to be that the cap cans you've used were both duds, or the startup surge from the 5U4 is exceeding the cap's 475V rating (or its cooking as mentioned previously - but would think is not so likely as cap can is outside the chassis on a stock PR and thousands of them have been made that way and the caps have survived for a long time. Weber used to sell a 4 x 20uF '500V' rated cap can IIRC - tho can't see it on their website. I'm sure I have one in my stash. Their cap cans are rated for 105C)

[sonicmojo]

I hear you. I've measured about 150F in my black on black Honda Civic on a sunny day. In fact, I recently used that car to kill live termites in a 70s Marshall head cab (termites eat amps a lot here in Hawaii). I'm wondering if heat like that alone would damage caps in an amp without it even being turned on. This is a good reason why I never leave gear in a car during the day.......

[Lauri]

Maybe those caps keep failing often at temperatures over 55C, hence the low temperature rating on the new ones. I would expect the whole chassis of an amp like that to get warmer than 55C after playing it for an hour or so. And if the can is near the power tubes it will easily heat up to over 65C and have a short life

[1955alick]

The Best F&T

[Roe]

The Best F&T

yes, here are FT multican caps: https://www.die-wuestens.de/

[Travis_HY]

I would invest in the F and T and call it a day. A 55C cap in a tube amp is a snowball in Hell.

[sonicmojo]

Those look good and I see they have a 30/20/20/20 at 70C.

I recently ordered with a JJ 40/20/20/20 also rated at 70C. Hopefully it fits in the hole okay.......