Date: Mon, 5 Jun 2017 06:36:47 -0400
From: Herbert Schoenbohm <herbert.schoenbohm@gmail.com>
To: amps@contesting.com
Subject: Re: [Amps] Tube amps are not a thing of the past
<Tubes in High Power Amps can take a licking and keep on ticking...but
not solid state amps devices. Replacing power MOSFETS in RF pallets is
much more complicated.
On 6/5/2017 3:46 AM, Roger (K8RI) wrote:
> OTOH as W8HW said, the input of the high power devices is extremely
> fragile. Over drive and spikes of very short (few Ms) duration that
> wouldn't faze a tube can be fatal for SS devices.
## a 4CX-1000 has ZERO watts of grid dissipation. A 4CX-1500B is
not much better, at only 1 watt. They both require fast grid over current
protection, like < 100 microseconds. A 8877 also requires fast grid
over current protection. ON4UN took out the grids in his hb 2 x 4CX-1500B
amp years ago...in less than the blink of an eye. The GM3SEK tetrode board
has grid overcurrent protection..works.
## Nobody ever blew the grid out of a 3-500Z. The 225 watt CCS grid
in both the 3CX-3000A7 and also 3CX-6000A7 are indestructible. With the
grid flange bolted to the cold chassis, the grid diss is further increased.
A buddy had his ipa go nuts one night, and it stuffed 2 kw into the
3x6..instead
of the usual 500-700 watts. Nothing happens. A simple 3agc rear mount fast
grid
fuse, wired between chassis and negative terminal of grid meter..or grid shunt
ensures
plenty of safety. Fuse opens up, no path for DC grid current, amp cant be
driven, power
output drops to zero watts, input swr rises to infinity, xcvr shuts down,
event over.
## I can see where the SS amp revolution is going to surpass tube amps, and a
lot quicker
than 5-10 years. More like 1 year, 2 max. Tubes will be relegated for high
power use, like
5-15 kw. Even 2 or 4 of these SS amps could be driven through a
splitter....then a combiner on the
output side..which has already been done. Then the pre-distortion sample
could be derived from
the output of the combiner.
Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|