Filter cap bleeding resistors: pros and cons

[Hardtailed]

Are there any cons to bleeding resistors?

On one hand, it "feels" good to know that you filter caps are always drained when the amp is not in use, but it also means they have to fully recharge every time you turn the amp on, causing additionnal stress and risking burning up fuses.

When I need to work on the amp, I can drain the caps myself, I can also temporarily hook a resistor to ground to make sure they drain if they "regrow".

Any thoughts on this?

Do caps last longer when charged most of time, or is it the other way around? (I think I've read that electrolytics are happier charged...)

[tubeswell]

I don't think it shortens the life of the caps at all. I have gone to putting bleeders on all my amps now. It doesn't make any difference to charge-up time from my observarions. The tubes take far longer to heat up that the filter caps take to charge

[conisat]

My way of thinking is it is a good idea to to have bleed resistors on the B+. For instance in a fixed bias set up with the B+ fully charged the negative bias set up has a bleed therefore when first turned on the bias caps (usualy quite large) need time to charge resulting in unsafe amounts of power tube current.
As for the caps being happy when charged ive never bought one that was pre charged and they tend to be quite happy, no need to worry.

[defaced]

Wouldn't leakage current in the filter caps eventually drain them after sufficient time has passed without a voltage across the terminals?

[Hardtailed]

Originally Posted by conisat

My way of thinking is it is a good idea to to have bleed resistors on the B+. For instance in a fixed bias set up with the B+ fully charged the negative bias set up has a bleed therefore when first turned on the bias caps (usualy quite large) need time to charge resulting in unsafe amounts of power tube current.
As for the caps being happy when charged ive never bought one that was pre charged and they tend to be quite happy, no need to worry.

My standby switch is after the first cap can, so on standby the bias supply is already working (and it's just 2 10uF caps).

They don't come pre-charged, but they have a "shelf-life" that is shorter that their life expanctancy when in use. I've read many times that an amp that is seldom played will wear out its filter caps quicker. Counter-intuitive I know, which is why I question the bleeders.

[conisat]

Originally Posted by Hardtailed

My standby switch is after the first cap can, so on standby the bias supply is already working (and it's just 2 10uF caps).

They don't come pre-charged, but they have a "shelf-life" that is shorter that their life expanctancy when in use. I've read many times that an amp that is seldom played will wear out its filter caps quicker. Counter-intuitive I know, which is why I question the bleeders.

Ive pluged in my amps once or twice with the stanby switch on (by accident). That is why I personally allways fit bleeds but i suppose it is a matter of personal preference. The only time it is definatly benificial to fit bleeds is when connecting caps in series to ensure an even voltdrop.
Defaced is spot on about leakage if you are not using am amp for great lengths of time they will have bleed of any how.
On the bad side of things i have had a couple of shocks in the past due to lack of bleeds that tends to influence my decisions. 450v DC is not nice I can tell ya

[tedmich]

good caps self bleed pretty slowly, but the Fender in the attic is likely safe (the bleed time is a pretty straight forward calculation, R(MOhm) x C(uF)=RC (seconds) 5RC is a down (or up) all the way, 0.22MOhm x 47uF = 10.34sec x 5 =51.7sec) I've heard the self bleed RC is >400sec depending on the circuit/cap etc.