I heard last week a 8877 from Richardson's was reduced from $2930.00
down
to $2k. (Eimac).
A Greenstone 3CX-3000A7 used to be $729.00. It's now up to $925.00
A 3CX-3000A7 is instant on, 50 ohm input Z. 50 watts of drive =
1.5 kw out.
IMD3 is -53dbc (-59db pep) @ 5 kw PEP output. NO parasitic suppressor
required. Instant on.
The 24.0 pf anode to grid C rises to 33.0 pf when tube is installed in
the grid ring. The extra 9 pf is from the proximity of the lower anode fins
to the chassis. The 33 pf stray C is easily dealt with on the upper HF
bands with the inclusion of a small value coil between plate block cap
assy..and C1 tune cap. The tube C + the extra small coil forms a step
down L network. This transforms the plate load Z down to a much lower
value, such that a practical low Q PI net can be used.
Econco told me on the phone that they could rebuild Eimac, Svetlana, +
Greenstone 3CX-3000A7....or any other Chinese 3CX-3000A7 tubes. Econco
sells Eimac rebuilt 3CX-3000A7's for $830.00 ( you provide the dud).
The 3CX-3000AA7 is still used in FM broadcast. Typ life on the filament
for 5 kw FM broadcast use is 35K hours (4 years). The cooling
requirements
are minimal for 1.5 kw output levels....including RTTY / FM / DATA /
FT-8. 1.5 kw output @ 60% eff requires 2.5 kw DC input...and 1 kw anode
diss. Typ efficiency on 160-40m is 68-70%..and decreasing a bit as freq
increases..
RF parts sells a superb chimney.... and an ( expensive $375.00)
socket....which also handles the bigger 3CX-6000A7 tube.
https://eaglemade.net/ makes a machined grid ring + mating 2 piece,
inner +outer collet for the filament...at a reasonable price.. Floyd
at Eagle made has a new 5000 sq foot machine shop. His
160-10m 230 uh ferrite loaded plate choke has been used up to 6kv on
all bands 160-10m. It's simple to make too, just type 43 beads .736" OD x
.400" ID X 1.125" (or 2.0") long, slid inside a hollow 1" OD (.75" ID)
Teflon tube. Wound with Teflon coated 22 ga ( silver stranded) wire.1"
OD x .75" ID hollow teflon tubing is available at Mc Master Carr. The
225 watt CCS grid dissipation is actually a lot more, with the tube in GG,
and grid bonded to the (cold) chassis.
For max cooling, a Dayton 6DKY9 blower (cheap) puts out an easy 80
cfm @ 1.2" backpressure. Eimac specs 67 cfm @ 1.2" back pressure for 4
kw CCS anode dissipation with an inlet air temp of 104 deg F. With lower
inlet air temps, and / or lower anode dissipation, the cooling requirements
drop through the floor.
Jim VE7RF.
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