I have a few questions:
1. Are the rectifiers SS or tubes?
2. Was the transformer originally built for a Full Wave tube rectifier?
That is with a center tap.
3. The AC line is measured right at the transformer terminals?
Using an old tube era transformer with SS diodes in a full wave bridge
can cause the symptoms you describe due to a high series impedence. A
modern xfmr designed for a FW bridge, with standard E-I laminations, is
capable of excellent regulation. I have one here that is 3900VDC no load.
At a 1A load it is 3600V and at close to 2A it is 3400V. The transformer
has a 2A ICAS rating and the filter cap is 24MF oil filled @ 4KV. It has
been used for over 6 years in some serious VHF work with nary a problem.
73...Carl KM1H
On Mon, 10 Mar 1997 02:17:42 -0500 (EST) QROKING@aol.com writes:
>I kinda had the feeling that someone would suspect poor line voltage
>regulation as a cause of the secondary DC voltage to sag heavily. I
>was
>going to mention that it was the first thing I checked. When I
>originally
>built the supply I had 25 amp fuses but I blew them to kindom come in
>a few
>seocnds of key down loading. I took care of that, and continued my
>investigation, I determined that under no load and a HV DC of about
>4300-4400
>volts being produce by a line voltage of 238 volts. At full load I
>measured
> the line voltage and it dropped to 229 volts, thats not bad since the
>line
>current is about 45 amps. So the problem is NOT primary line sag.
>Bill Orr
>claims in his book, that the regulation of the DC from the rectifier
>is much
>tighter when the increase in filter capacitance. Like I said he
>recommended
>80uf for my specs. I had 120uf and did not get the 5% regulation he
>talked
>about. I know that all power supplies drop considerably when loaded
>heavy
>but this supply has all the goodies to prevent that. I am leaning
>towards
>the theroy that since the secondary AC voltage on the transformer is
>3000,
>that is the effective voltage and will be the only "heating power
>effect"
>voltage. The 4300 volts after the rectifier is 1.414 of the 3000,
>but that
>is the peak of the 3000, and the peak will not offer any effectiveness
>to the
>"heating effect" so a voltage drop should be expected near that 3000
>vac
>value. Also, since SSB has become popular nobody uses choke input
>filters
>any more. Now as I recall you dont get that rise in voltage with a
>choke
>input filter. So maybe I should count my lucky stars I have a few
>hundred
>more than the effective 3000. So what say anybody?.....73 LOU
>
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