Leaking cap in ST 70

Hello All,

I was looking under the hood of my vintage ST70 with VTA board recently and noticed that the .1 uf cap at C1 was looking a little odd;  misshapen outer cover and whitish-looking accumulation along the top (facing) side.  This Solen cap is original to the VTA board install, which was about 7 years ago.  The C2 cap also appears to have a similar white accumulation on top, though it is not misshapen.  I have ordered replacements for the caps, but am a bit surprised that these are dying what appears to be a premature death..  

Is this common/uncommon or possibly symptomatic of another issue with the amp? Any input / related experience welcome.

Thanks,

K.

I've never liked Solen caps. I've used them, but for the price I believe there are better caps than the Solens, plus I've heard that other people are having the same problems you have. I doubt that you have a problem with your amp, replace the caps and you should be good to go.

first I've heard of bad Solen caps, or them not sounding good, for the price they are hard to beat, but I switched to Audyn about two years ago as they are similar for about 60% of the Solen price.
Also Jensen makes a similar cap. Much better caps are the Mundorf EVO series for about $8 each.

My go to caps are orange drop either, 715p or 716p as they are good caps for a good price. I've tried some of the supposed audiophile caps and to my ears, they don't sound any better than the orange drops.

715P are OK but not great. 716P are excellent and a real bargain

weird that those caps went bad.  The amp doesn't seem to get hot (tranny temp) but those two caps look pretty baked! I may try to post a pic later if it's not too complicated. (see link below)

Muchas gracias,

K.

https://i.gyazo.com/f146666c7082ed38c07c110d461a18dc.png

I use the 715P orange drop caps in most of the equipment that I restore as in my opinion, they are far superior to anything used in the 40's, 50's and 60's, plus they are reasonably priced. The 716p cap is a better cap and is priced accordingly, but works really well in recently built equipment and on par with the boutique audiophile caps for less money.

Dingojazz wrote:Hello All,

I was looking under the hood of my vintage ST70 with VTA board recently and noticed that the .1 uf cap at C1 was looking a little odd;  misshapen outer cover and whitish-looking accumulation along the top (facing) side.  This Solen cap is original to the VTA board install, which was about 7 years ago.  The C2 cap also appears to have a similar white accumulation on top, though it is not misshapen.  I have ordered replacements for the caps, but am a bit surprised that these are dying what appears to be a premature death..  

Is this common/uncommon or possibly symptomatic of another issue with the amp?  Any input / related experience welcome.

Thanks,

K.

Was the caps actually electrically leaking ? Or is it a visual thing on the surface of the caps ?

Hullo All, and thanks for the replies.


-Physical damage rather than electrical leakage. Looks like the outer wrap split open, revealing whitish substance like dried glue on top (facing the underside of the board).  I was not able to post a photo directly, but managed to insert a link in the post above for a look at the damaged caps. The amp sounded ok, at least as far as I could tell, but I decided not to take a chance.  I've never seen something like this... maybe heat damage?? My amp doesn't get hot, at least never too hot to be able to rest fingers on it for a spell.  

Commentary welcome.

Cheers,

K

I would be interested to know whether or not the caps just look bad or are actually damaged electrically such as an insulation failure causing internal electrical leakage. But that would require the use of a cap tester such as a Sprague Tel Ohmike TO6 to supply the necessary voltage to test for insulation breakdown.

Big Harry wrote:I would be interested to know whether or not the caps just look bad or are actually damaged electrically such as an insulation failure causing internal electrical leakage. But that would require the use of a cap tester such as a Sprague Tel Ohmike TO6 to supply the necessary voltage to test for insulation breakdown.

Or an in-situ measurment with a vtvm to detect any leakage.

Ya, well, I have a digital VTM that does test caps, but that may just be the uf rating rather than for "leakage" (?).  

Otherwise, as noted I didn't hear any distortion or other oddities - the problem may not have risen to that level, and maybe subtle "leaks" aren't audible.  I have replaced these with K40s, and everything sounds peachy.

One thing's for sure, they LOOK fugly...!

Have others come across this?  -Root causes?

Thanks,

K.

The modern cap testers do a good job of checking capacitance, but an older style tester that was used for testing of caps in vacuum tube electronics is what is needed to accurately test the higher working voltage caps. The modern testers are usually powered by a 9 volt battery which won't tell you much about the insulation resistance in a 400 or 600 volt cap which is a necessary test to give a good indication of the condition of the cap.

Dingojazz wrote:Hello All,

I was looking under the hood of my vintage ST70 with VTA board recently and noticed that the .1 uf cap at C1 was looking a little odd;  misshapen outer cover and whitish-looking accumulation along the top (facing) side.  This Solen cap is original to the VTA board install, which was about 7 years ago.  The C2 cap also appears to have a similar white accumulation on top, though it is not misshapen.  I have ordered replacements for the caps, but am a bit surprised that these are dying what appears to be a premature death..  

Is this common/uncommon or possibly symptomatic of another issue with the amp?  Any input / related experience welcome.

Thanks,

K.

The "outer cover" is just a piece of heat shrink with the cap info printed on it. It can get distorted by exposure to a lot of heat. It happens in the Citation II amp where I use them to replace a 4 uf electrolytic screen bypass cap, so I am quite familiar with what you are describing.

Below the heat shrink is a gray epoxy which is quite durable and has not shown any signs of distress even in the very warm location the caps are found in the Cit II. The caps are rated at 85 C (185 F) so all you are seeing is the shrink warp distorting. It's not an issue other than aesthetics.

I'm not sure what the white material is but it may simply be residue from under the heat shrink.

As others have suggested, a proper test of the cap for leakage, DF, capacitance, etc. will clarify the situation. But I strongly doubt there is anything wrong at all, especially since you didn't mention any performance issues with the amp. If the heat shrink shriveling bothers you then cut it off with a razor blade - just write the cap values on the epoxy with a permanent marker after you remove it.

Thanks, Jim et. al.,

That is useful information, and goes a long way toward explaining the appearance of the caps.  
Good to know that they're heating up, not 'blowing' up.

Now that they're replaced with K40's, I like the sound better, as they seem to have smoothed out some of the Solens' harshness.
Now, let 'em try to melt those babies!!

K.