Jack Schmidling wrote:

My new (first one in 50 years) is an 8000 modulated by a pair of 813's
running as triodes. The RF deck and Pw supply are up and running and I
am working on the modulator now.

My plans are to drive it with the Ranger and eventually do a stand alone
audio section. The Range gets poor audio reports in spite of months of
trying to resolve it.

I am wondering if anyone here as any experience using 813's as triodes
and would also like some help on the audio driver.



I bought a little solid state audio pre-amp and driver that puts out
about 4W at 8 ohms. This is probably not enough to drive the 813's so I
need more poop and some ideas on how to drive the modulators with the 8
ohm amp.

There are some in progress pics of this project at
http://schmidling.com/radio.htm


Jack K9ACT


If I have my numbers right, a peak envelope power of 1500 watts equates
to a carrier power of 375 watts, which requires an audio amplifier to
put out 200 watts (to round up a bit).

If the 813's were wired as pentodes they could deliver 600 watts in AB-2
with less than a watt on the grids. I'm not at all sure of what you'd
lose using them as triodes, but I'll bet they'd deliver 200W in AB-1
with no grid power consumed at all.

Antique Radio Supply (www.tubesandmore.com) has a reprint of an RCA
transmitting tube handbook that has extensive data on the 813 -- it
should have enough data in there to figure out the design stuff, and
directions in the front on how to use the data.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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