VH4 Filter Cap Question

webrthomson

I had my VH4 out of it's headshell to test the tubes as I've been getting odd noises and right enough a preamp tube was on the way out.

Now while I had it out I noticed that the three filter caps in front of the power tubes have slightly rounded ends (the one on the right hand side of the amp is perfectly flat), like so:





Does this mean they are needing changed - they caps are dated 07/07 and the amps is a 2008 serial so that ties up.

The bulge is about 2mm or so - any input would be greatfully recieved as I'd rather get them changed if they are on the way out than they leak / blow!

Incidentially the amp still sounds utterly amazing

ICBM

I see this quite a lot, and it doesn't seem to mean anything bad - just that the plastic has got hot and expanded slightly. It's not the cap starting to vent gas or electrolyte because the seal is at the other end. It used to worry me when I first started seeing it, but it doesn't seem to correlate with failures.

The cause here is the caps getting heated by the radiant heat of the power valves - which is not good for them really, but most valve amps do run the caps quite hot - which will be why the one at the end hasn't been affected yet, as it's further from the centre of the line of valves.

At only ten years old there is certainly no need to change the caps if there are no signs of actual trouble, contrary to what you may read online - twenty to thirty years is more like it, and even that's pretty conservative. I often work on amps with caps over forty years old that *seem* to be fine... although I do normally change them at that age.

DJH83004

+1 for IC's comments, it's is just expansion of the plastic top caps due to general heat, if the cap was gassing then it would blow the top off the aluminium can and make a real mess ( trust me It does!!).
So no worries and keep rocking      

webrthomson

@ICBM ; and @DJH83004 thanks chaps, thats reassuring

I did think it seemed a little early to be failing - I've recently had them changed in my Marshall JMP and that is the same age as me, 41!