Re: 811A any good?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi Jan, Matt, Ralph!


Date: 23 January 2001 19:59
Subject: Re: 811A any good?


>Your right that the average power rating for the 811A is
"45W CCS and 65W ICS
>averaged over any audio-frequency cycle of sine-wave form".
Maximum plate
>input (pulse peak) is in the range of 230-260 Watts
(radar-type
>applications). It's usability depends critically on the
type of circuit and
>the type of signal.


I think there's slight confusion here over power output and
plate dissipation.  The 45W CCS and 65W ICAS ratings refer
to the amount of power which can be lost in the anode of the
valve as heat.  RCA's "Transmitting Tubes" manual (I have
the reprint) makes it clearer - under ICAS conditions and
class C biasing, you can put 260W into the tube, the plate
dissipates 60W as heat and 200W rf comes out, *continuous
wave*, per tube.

I suspect our friend Terman would say you can squeeze a fair
bit more under low duty cycle operation, e.g. ten
microseconds on, ten milliseconds off.  Is that what John
Freau does with his massive 833 coils?  I currently have a
pair of 813s awaiting similar treatment as and when I get
the time.  I anticipate 750W out (cw) from the pair with any
luck. But no idea when I'll get the proverbial round tuit.
It may be some time.

Dunckx