Hans said:
>As far as I remember these tubes have graphite anodes
All my 4-400s have metal anodes (Eimac, Penta and a Siemens). The Siemens one
surprises me - I'd have expected graphite....
I use a single 4-400 in gg on 10m. I found that it needs about 3.7 - 3.8kV to
give about 470 - 500 watts: I can't remember what the IMD is like, but guess I
could measure it if anyone is really interested. Just have to cart the spectrum
analyser to the rig.......
The emission capabilities of the 4-250 and 4-400 are the same; the
characteristic curves in the Mullard book appear to be so, too. I use a pair of
4-250A (actually QY4-250) in grounded cathode AB2 with negative feedback and
stabilised grid and screen supplies very successfully on 24MHz and below. But it
likes about 3.8kV on the plate. I get (from memory) -32dB rel each tone from
that amp at 900 watts PEP.
73
Peter G3RZP
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