[AMPS] 813 question

[Larry Molitor]

At 10:55 AM 10/3/99 -0400, you wrote:
>
>Is the input impedance of a pair of 813 tubes, grounded grid configuration,
>close enough to the magic 50 ohms to accept power from a modern exciter with
>simply a parallel low-Q circuit shunted from input to ground?  I sure hope I
>do not have to work up a pi-network for each of three bands.  Thank you, 73,
>J. Fisher K4GF

A single 813 running in TCGG has an effective cathode input impedance of
270 ohms at any reasonable anode voltage. Two would be 135 ohms, four would
be about 67 ohms. Go ahead, put in the pi-net. Do it right. It only takes a
few extra minutes for each network and it will pay off in the long run.

Two 813's in TCGG are nice. As Skip said, four are just short of wonderful.
I have one amp in each of those configurations. You can see the 4 x 813 job
on the AMP PIX page.

Have fun!




73,

Larry - W7IUV
w7iuv@arrl.net
http://www.axtek.com/w7iuv
Amp pix at http://207.108.137.61



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