> I notice the stock 200 uf @ 450 vdc caps in my 4 x old 1977 era Drake
> L4B's seem too last
> forever. B+ on em is 2650 vdc NO load on RX. 2650/3600 = 73.6% A
> heath SB-220 and similar
> amps with the same 8 x 450 vdc caps, run at 3300-3600 vd.... don't fare
> as well after yrs of use.
>
** The Drake secondary is 780/1065 VAC. The Heath is 860/1171 VAC. Where do
you get your numbers from?
## all 4 of my drake L4PS are 670/ 940 VAC. I know several Ameritron
owner's,
whose B+ is 3600-3790 vdc.. depending on their line vac. I know of a few..
who
moved to a new home.. and vac was as high as 257 vac.. and caps exploded !
With the
line vac up to 247.. a heath sb-220 can easily hit 3550 vdc. The
ameritrons are maxed
out.. with just 240vac.
** Most of the SB-220 series I get thru here have good original caps. Get
rid of the 30K heaters and go with 100K MOX and verify that the voltage
deltas arent excessive. I use the standard Mouser 5% Xicon, no need for 1%.
## I have had 5% tol.. that were 4% low... then the next batch are 3.9 %
high.
IF you have caps that are almost maxed out [due to excessive line V]..
it works out nicely to at least have better matched eq resistor's.
## The deluxe 1% tol resistors... [ that are actually .1%] were relatively
inexpensive. It was getting tedious.. trying to matchup 24-30 resistors..
then repeat 8 x more times.
I can afford the extra 2 bucks buying a box of 1% resistors... since I
didn't drop $10K on an Emtron. lol
** Amazingly Im still getting mid 60's NCL-2000's in with original caps.
National used a custom built 80uF 450V rated for high ripple current, about
an inch longer than a comparable Sprague Atom.
## OK.. how do they work with real caps in em... like 560 uf variety ? ..or
bigger. The screen HV cap in the NCL-2000 wasn't too big either. Think
the NCL-2000 uses 6 caps for the Hv ?? That's only 80/6 = 13.34 uf...
that's like 6% ripple.
later... Jim VE7RF
Carl
KM1H
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