-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim Thomson
Sent: maandag 26 januari 2015 17:40
To: amps@contesting.com
Subject: [Amps] push pull or parallel ?
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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Hi Jim (and others who did reply)
It is a monoband 160mtrs amp. Output power is at the moment limited by screen
current, so surely not running it to the limit. Reason: we don’t want to retune
as we change QRG (1810 - 1900).... Screen current will increase of course when
Zload is not optimum. Also running the PI-L match already at rather low loaded
Q (8 or so). Normally we see the amplifier twice each contest...at the start
and at the end...located in other room.
Would be interesting to learn if in that respect parallel operation is behaving
different than push-pull ?
73's Carel.
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