Date: Thu, 28 Mar 2019 15:42:54 -0500
From: Rob Atkinson <firstname.lastname@example.org>
To: "email@example.com" <firstname.lastname@example.org>
Subject: Re: [Amps] Replacing padder caps on an Alpha 77DX/SX
I would imagine that a 500 or 750 pF doorknob that could handle the current on
160 meters is at least $150.00 or more.
You imagine incorrectly. Even brand new HEC 15 KV is about half that price.
That is why modern amplifier manufactures don't use them. They use what I used,
and more likely surface mount types on a small circuit board.
<No, they don't use them because hams are cheap customers, most don't
know any better, the duty cycles are usually low, and manufacturers
buy in lots of 1000 or more. But a single ham with one amp can afford
## Typ HT-50 + HT-58 door knobs in the 5 / 7.5 kv variety are in the
$12.00 to $14.00 range..in single lot quantities.
Buy them in huge quantities and prices drop like a rock. A single HT-58
in 700 pf, would easily handle the required current
as a padder on 160m... and still not drift. Screwing down the HEC doorknob
to the chassis heat sinks the doorknob, increasing its
current rating. Although caps with better temp coefficients are preferred
as padders, this is normally not required. IF the padder
in question has more than ample current carrying capacity, the cap wont heat
up in the 1st place. Once that is factored into the equation,
drift becomes a non issue.
## The 15 kv HEC doorknobs Rob is referring to are called HT-57s...and
typ cost $40.00 Again, in single lot quantities. Not required
for a padder application. 20 kw into 50 ohms is only 1414 Volt peak.
## Forget ham amps, look at how commercial amps are built, they use the real
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