Date: Mon, 26 Jan 2015 16:41:48 +0100
From: "Carel, pc5m" <pc5m@xs4all.nl>
To: <amps@contesting.com>
Subject: [Amps] push pull or parallel ?
Hi,
160mtrs contest past and we need more power... Plan is to add 3 dB by
throwing in another tube (2.5kw anode dissipation Tetrode, grid driven).
I could go for push-pull of just parallel the tube's. I think push-pull
would be nice to get less even harmonics, but seems to be a big hassle and
just put the tube's in parallel is much easier. Or am I missing something ?
73's Carel, pc5m
## is this a monoband 160M amp...or multi band ? How much drive do you have
available ?
The problem with doubling the power output is, you double the plate current,
and the plate load Z
will drop in half. You now require twice as much tune and load C....and half
as much tank coil,
assuming a PI net output. IF it’s a monoband 160m amp, no big deal, just pad
both caps, and
replace the coil with one that has half as much uh. If it’s a multiband amp,
you can still pad
both caps on 160m, via vac relays, but you will have to watch the peak V across
the vac relay contacts
on the tune padder, when on 80-10m, esp the high bands. vac relay peak V
rating drop,
as freq increases. Coil will be one half as big on each band, but with double
the rf current through it. .
## I think push-pull will work on a monoband amp...dunno about multi band.
With 5 kw
anode diss, maxed out, and assuming 65% eff on 160m, you should be able to do
14 kw dc input,
and 9.1 kw output. (= 4.9 kw anode diss).
## 160m is pretty forgiving for the most part, with long leads etc. Is this
a CW or SSB amp...
or both ? If its cw or for a cw contest, you can always increase the TX bias,
and reduce idle
current quite a bit.... and increase the tank eff.
## 3db is not a huge amount. If instead you tripled the po, then you get
4.77db...which is
a well worthwhile increase. 3db would be enough to get you through in
most cases, and is a good starting point. 4 X = 6db. Now you have a
substantial increase.
You can only do so much with 160m TX ants.....after that, more PO is required.
You cant
work them...if they cant hear you.
Jim VE7RF
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