[Amps] Replacing padder caps on an Alpha 77DX/SX

[Jim]

Put your money where your mouth is Jim..

Please send a link that includes prices that I can order.

Thanks
73
Jim W7RY

On 3/30/2019 1:51 PM, Jim Thomson wrote:
> Date: Thu, 28 Mar 2019 15:42:54 -0500
> From: Rob Atkinson <ranchorobbo at gmail.com>
> To: "amps at contesting.com" <amps at contesting.com>
> 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
> quality.
>
> <73
> Rob
> K5UJ
>
> ##  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 deal.
>
> Jim   VE7RF
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