----- Original Message -----
From: "jerome schatten" <romers@shaw.ca>
To: "Carl" <km1h@jeremy.mv.com>; <jtml@vla.com>; <amps@contesting.com>
Sent: Monday, September 07, 2009 12:13 PM
Subject: Re: [Amps] 304TH, 304TL, 813
> 1. How to tell if the 813 has graphite or tantalum plates? I have one
> pair from the early '40's and one pair made in the early 60's; I rotate
> them every year or so.
Very easy, look at them. The graphite are thick and look like a hunk of
carbon.....which they are. Similar but larger than a 572B.
The others are thin sheet metal.
>
> 2. Amp runs only on 80/40/30m at 2200v, grids strapped to chassis; zero
> bias; no suppressors. The pi output circuit uses a very robust variable
> inductor (square copper wire) that progressively shorts out un-needed
> turns. Does it make any difference which end (plate or load) the shorting
> of the turns takes place?
Do the progressive shorting from the Load end.
>
> 3. Fan sucks the hot air out from the top right above the tubes; should I
> be blowing air in instead?
Fans are more efficient when pulling air, take a look at the electric fans
in your auto. In your amp it doesnt matter as all you need is a small
movement of air.
>
> All these things I never thought about when I built it almost 50 years
> ago.
I built my first KW amp in 57, PP 250TH's, fans were for rich people!
Carl
KM1H
>
> jerome - va7vv
>
>
>
>
> On Mon, 07 Sep 2009 08:24:38 -0700, Carl <km1h@jeremy.mv.com> wrote:
>
>> There are some running 813's at over 3kv daily on AM; I didnt ask if it
>> is
>> graphite or tantalum plates. I run close to that with graphite plates
>> and
>> never a hiccup.
>>
>> IMO, the 813 is a highly underated tube and Pd with a bit of air is
>> easily
>> 250W.
>>
> [...]
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