I sent a rather long message last week about this subject but it seems to
have gone the way of the dinosaurs.
To recap in as little of space as possible:
- MANY hams attempt to utilize transformers designed for tube
rectifiers and full wave service with a pair of 866 or 872 rectifiers as
an example.
- Most of those transformers were designed for choke input service
and had caveats for capacitor input use.
- Most of those antique (anything over 25 years) transformers with
their center taps, etc have a high series impedence or resistance as
compared to modern transformers. I dont want to get into a long winded
discussion here about impedence vs resistance, suffice it to say that
"something" is different.
- A transformer built in say 1955 with a 2200-0-2200 VAC secondary
at 700ma CCS will not be that magic transformer for a single 4-1000 at
6KVDC as an example. With a modern SS FW bridge rectifier and ANY
reasonable amount of C, that "typical" antique will/can drop 1000V under
full load. I've been there and watched them blow up before I understood
the issues.
- A transformer designed for tube rectifiers in a FW circuit can
still exhibit a substantial voltage drop when used in a FW SS bridge
circuit even when operated under the same Kva ratings.
If Ive added confusion, Im sorry. This has been a confusing subject for
many ever since SS diodes became popular. I use a modern xfmr with a
2700VAC secondary @ 2A ICAS for various VHF/UHF RF decks. No load DC is
about 3900V. At 1A it is 3600V and at almost 2A it is 3400V. The total C
is 24MF (2 x 12MF @ 4KV oil filled).
IMO, a PS choke is a complete waste of money and resourses unless it is
for an AM amplifier or modulator. Henry Radio has its fans.....so fire
the flame throwers. It is more cost and performance effective to
design/utilize the transformer and the complete PS around the
application.
73...Carl KM1H
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