[Boatanchors] Gonset 972A

[peter markavage]

I run about 3 watts, of maybe a hair more, to drive either the 903 or 913
amps. Enough drive to just tickle the grid current reading without moving
it off the zero reading.

Pete, wa2cwa

On Mon, 02 Jan 2006 18:21:28 -0700 rayfri <rayfri at highstream.net> writes:
> Found a couple comments online about the 4X150a ... Apparently one 
> might 
> expect 250 to 300 watts output (500 PEP) with an AC supply... SO, 
> does 
> this mean that I should cut my two meter driving power down to about 
> 
> half a watt? Doesnt look like I should
> be punching this thing with 30 watts of FM power....
> Ray
> 
> Push Pull Class AB2 Amplifier
> Plate Voltage ................................. 1250 V
> Grid No. 2 Voltage ............................ 300 V
> Grid No. 1 Voltage ............................ -44 V
> Peak Grid No. 1 Voltage........................ 100 V
> Plate Current ................................. 475 mA
> Grid No. 2 Current (Zero Signal) .............. 0 mA
> Grid No. 2 Current (Maximum Signal) ........... 65 mA
> Driving Power ................................. 0.15 W
> Load Resistance ............................... 5.6K ?
> Power Output (approx) ......................... 425 W
> 
> A 4x150A-4CX250B-4CX250R family tube will actually put out 500W PEP 
> 
> okay, if used at maximum plate voltage in a high-efficiency circuit. 
> The 
> old rule about power tubes, where output power is generally 2x the 
> plate 
> dissipation rating, holds up pretty well. 2x 250W = 500W. The 
> problems 
> with this tube are:
> 
> -Doesn't work well in grounded grid, so grid and screen supplies, in 
> 
> addition to a HV supply for the plate, really are required. This 
> complicates power supply design and construction.
> 
> -They have enormous power gain, so with a tuned input it's easy to 
> run 
> "full power" (e.g., 500W PEP output) with only 3-4W of drive. 15W 
> would 
> be *waaay* too much, in many cases. You only need about 55v peak 
> grid 
> voltage to drive this class tube to the limit, and with a tuned grid 
> 
> input network, it's easy to hit that with only a couple of Watts of 
> 
> drive. Thus, it's really easy to overdrive this tube -- and destroy 
> it 
> in the process.
> 
> -They have a really puny grid and screen dissipation rating, so 
> without 
> a lot of prevention circuitry it really is easy to destroy by small 
> 
> cockpit errors. On the other hand, I have homebrew 4CX250B 
> amplifiers I 
> built in the 1970s which have thousands of hours of use on them and 
> 
> still have the original tubes, running fine. It's a matter of 
> monitoring 
> grid and screen currents and knowing how to control them.
> 
> 
> Glen Zook wrote:
> 
> >It uses the 4X150A and operates primarily in AB-2.  It
> >was made for mobile operation and has a 12 VDC
> >built-in power supply.  According to my references it
> >puts out about 90 watts peak on SSB and 120 watts on
> >CW / FM.  SSB drive power is about 5 watts and CW / FM
> >is 30 watts.
> >
> >Original cost was $299.00 and there was an
> >installation kit that had a control head, cables,
> >etc., that cost $59.00.
> >
> >Glen, K9STH
> >
> >
> >--- rayfri <rayfri at highstream.net> wrote:
> >
> >Turns out it is not a 903 or 903A, but a Gonset 972A. 
> >   Anyone familiar with it?    The ID tag says 144 to
> >174 mhz....