"Paul" bravely wrote to "All" (08 Apr 05 14:45:04)
--- on the heady topic of " Multi-section cap's for Scott 299B tube amp =
restoration"

Pa From: (Paul)
Pa Xref: aeinews sci.electronics.repair:45278

Pa Thanks to all who took the time to reply. Unless I find a cheaper
Pa source for replacement multi-cans, I will probably gut the old can(s)
Pa and stuff them with new cap's as Sam suggested. It is a fairly
Pa shallow and crowded chassis, so adding parts underneath would be
Pa difficult.
Pa Any comments regarding the need to replace based on the measured ESR
Pa values? If not, I'll probably replace only the dead ones at first,
Pa and see if here is any hum.

Pa On 'lytics that have not seen voltage for many years, I know that I
Pa should bring the voltage up slowly the first time. Should I expect
Pa the ESR to change after the first few charging cycles?


Paul, the matter of what amount is ESR is acceptable depends on the
expected working voltage and current. Older tube amps used high
voltages with low current and required less capacitance but thicker
dielectrics which typically results in greater ESR than a low voltage
high capacitance electro.

For example in a 350 volt DC supply that has 15 volts of ripple with
50mA, then 7 ohms ESR will add about a negligable 1/3 of a volt.
However, conversely if an electro is used for cathode bypass then that
same 7 ohm ESR might upset circuit conditions significantly.

Further some ESR meters may have a source of error giving a higher
reading with smaller value capacitance due to the test fequency being
too low (adds capacitive reactance to ESR) or too high (adds self
inductance from spiral plates).

On the matter of re-forming an electro, if the seal looks clean then
there is a good chance of success, and yes ESR will decrease a lot
once the electro is re-formed. Just remember a somewhat higher ESR is
to be expected with the higher voltage electros and might be normal.

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.