Bootstrapping replacement caps

[angelodp]

Hi, what is the efficacy of simply bootstrapping new caps (parallel) onto a circuit with older B+ caps. I was able to clean up the hum in an old Dukane amp by simply paralleling a 22uf on the first B+ node. Its a P to P amp so a bit congested at the second cap can. I can easily strap new caps throughout. Just wondering if this is a poor plan as the leaky cpas will still effect the circuit.

[thetragichero]

ever seen the inside of an amp where the old dried out filter cap blew? not a fun cleanup

[martin manning]

Yea not a good practice. The old cap will continue turning into a resistor, drawing more current, getting hot, and...

[xtian]

Yeah, bad idea. The older caps' ESR will likely be higher than the new ones, and will dissipate more current as heat, until, as Angelo says, "not a fun cleanup".

EDIT: Dammit, Martin for the win.

[pdf64]

Just to note that you're asking about connecting caps in parallel; 'bootstrapping' is a specific circuit technique used in the long tail pair etc, and so is something completely different, eg http://www.valvewizard.co.uk/acltp.html
and see last paragraph http://www.valvewizard.co.uk/dccf.html

[angelodp]

Ok I get it, out they come. In goes the new.

Thanks and thanks on the bootstrap definition.

A

[sluckey]

Hi, what is the efficacy of simply bootstrapping new caps (parallel) onto a circuit with older B+ caps.

The term you needed was bridging.

[angelodp]

Ok so both cap cans have various grounds from surrounding tube components. Once I build a board and populate the new electrolytic caps, does it make sense to leave the various grounds in place and run the new cap grounds to their respective points. The old cap cans would be left in place without any connections, the twist tab grounds remain with the associated grounds. Or is it better to pull the cans altogether and redo all the grounds (PITA). Just want to get this right.

A

[Phil_S]

I remove the old can caps when I do this sort of thing. I generally strip the chassis and start over. I find it simplifies things. You don't need to be stuck with Dukane's less than optimal decisions about where to ground stuff. Remember, it was a PA. They probably tolerated some hum.