> Is there experience here with using 813 in triode connection?
There are numerous amplifier articles using the 813 that have been
published in the past.... QST, Radio Handbook, ARRL Handbook.... etc.
Older Handbooks are a great place to start off.
>The 813 is a very rugged tube and has the reputation of being
>almost indestructible in amateur service. It is common to use it as
>a triode. The main limitation of the 813 in conventional circuits is
>reduced efficiency on bands above 20M.
Pretty hard to kill one. I've run them as single, dual, and quad.
I shouldn't say this, but it was not uncommon to operate with an anode
supply in excess of 4kv on the quad set to burn a good path for the
Wescars check in with "uncle Bill". Not to mention the late night check
in with "Hank, W2LTP for "The Triple H Net". We could buy the tubes for
$2 each at the flea mkts. Never lost one in service, even to the
excessive Pv.
>ZL1AXB has successfully used a circuit which tunes the filament
>and this improves the efficiency dramatically. This tuned cathode
>network takes the form of a bi filar circuit, and eliminates the
>usual filament RF chokes. ZL1AXB demonstrates key-down >400W
>output on 10m with a single 813 with Pv of 3000v.
I never had a problem driving the tube(s), the above amplifier circuit
was also written up in a book called 101 Easy Ham Radio Projects, circa
1960's or early 70' by K2AES. The tuned filament is also described for
use with an 811A circuit and 3-500z circuit in some Handbooks and used up
to 52MHz with success.
My single tube amplifier put 413 watts into a 50 ohm load on 7.255MHz. I
have placed them in operation in the horizontal plane with attention to
the mfgrs recommendations for said operation.
>The cathode circuit is described in an *Eimac* amateur service
>newsletter #AS-6 by W6SAI, W6KEV, and W6UOV. Some of the material
>may have appeared in QST August 1961 p16-21, but I have not checked
>this.
>Regards,
>Martin ZL1ANJ
Indeed,
I have the entire set of newsletters here in front of me, tittle "The
Grounded Grid Linear Amplifier". The last printed page shows three
circuits, the bi filar circuit that I've used. The second is the more
conventional pi-net and the third a shunt LC.
Recommended Q of 5 with reduction down to 2 or 3 when the physical limits
of the circuit are "bulky" at lower frequencies.
My shunt design was a brass tube (removed from a scrapped Perkin Elmer
GC) with teflon wire down the center before the coil was rolled. Don't
use RG-58 coax center conductor in the center of the coil. It melts much
to easy.....
Cheers
skip wv6f
nospam4me@juno.com
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