[Hammarlund] Oil-Filled Caps (BC-779)

[Al Parker]

Hi Joe, et al,
    Thanks to Chuck McGregor, I stand corrected, don't use 450v caps.  I
hadn't ckd the schem & voltages, was shooting from poor leaky rembrances.
    privately, to avoid my public embarrassment he said:
---------------------
"TM11-866, page 61,  shows 415v ac on each rectifier plate (measured
to gnd), for nominal line voltage conditions and under normal receiver
load.  That amounts to about 567 volts peak at the rectifier.  All we have
to pull that back down is the forward drop across the 5Z3....which under
load is around 50-60 volts. So we have about 507 volts peak, at the input
capacitor, under nominal conditions.   (The TM shows 450v DC at the input
cap, under these nominal conditions....which seems low...for these
AC  voltages ahead of the rectifier..).

If we allow for 10% high line voltage that would get us up to 557 volts
peak.  If we consider that somebody might foolishly apply power to the
power supply with the receiver disconnected that could add another say,
10%,  getting us up to 613 volts peak.

And, I haven't mentioned, whatif....somebody plugs in one of those cheap
silicon diode rectifier replacements....  So, no way, would I use a 450
volt electrolytic for the input cap in that power supply."
----------------------------
  Thanks Chuck, I owe you again.  (& I"ll fill you in very soon on the
R-388 project)
73,
Al

----- Original Message ----- 
From: "Al Parker" <anchor at ec.rr.com>
Sent: Saturday, January 20, 2007 2:53 PM
Subject: Re: [Hammarlund] Oil-Filled Caps (BC-779)


> Hi Joe,
snip
>     600v is a bit over an overkill, but probably an easily reached  no.
> for oil filleds.  If you replace with electrolytics, use something at
> least 10% over the actual voltage.  450v for the HV, lower for the
others,
> but if one of the bleeder/divider resistors fails, you might get full HV
> on the LV section, I don't remember exactly the setup.
> 73,
> Al, W8UT