Unless I missed something, the Centurion doesn't have a safety to
ground choke (which sort of surprises me). I don't know if that is
unusual among manufactured amps or not. Padding caps on the tune
cap, (C1) is something I am not very much aware of. I find it common
to pad the air variable cap on the Loading side but always thought the
range needed on Tune was typically not that much, maybe up to around
600 pf with high breakdown voltage needed (depends on the tube and Ep
though).
The thing with rx and idle plate current got fixed a long time ago.
That was an early mod Ten Tec made. That amp you saw (VE7RF) must
have been one of the first ones produced back around 1990 or late 80s,
whenever they first started making them.
The amp is a pretty good amp in my opinion for a pair 3-500ZGs but as
with all manufactured amps, it could be made better. I like the lower
Ep, around 3.1 KV resting (I used to think it could be higher but I
knew less then) and I like the plate choke they use, and the
bandswitch and tank components. I wish the cabinet were bigger, and
that they used a more robust h.v. transformer, and higher volume air
moving through the cabinet. The transformer and fan are not too hard
to change. But like almost all manufactured amps now, the price of a
new one is way high.
Before I ramble on too much longer, let me get to the main point I
wanted to make here:
On the Centurion you can add an extra fixed value load pad cap that
only gets switched in on 160. There is an unused lug on the
bandswitch that only gets contacted by the throw when it is in the 160
position. it's pretty easy to get in there and solder a wire (TT uses
silver teflon insulated wire) to that lug and snake it down to the
grounded lugs on the bottom of the cabinet under the variable cap
where the other 2 KV disk ceramic pad caps are located. there is
room down there to stick a mica or what Carl recommended in there. I
tried 250 pF and that shifted the Load sweet spot down from high up
near max variable cap mesh to around 30% of maximum variable mesh on
1880. So you might want to try 150 to 200 especially if you use the
amp down near 1800.
The loading is still fairly broad, but maybe some of that goes with
tuning a class AB stage instead of class C and using a pi network that
attempts to cover 1.8 to 30 MHz.
73
Rob
K5UJ
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