[Boatanchors] Gonset 972A

Tue Jan 3 01:59:17 EST 2006

Don't forget the air! I run a pair of 4CX250B tubes on 144 on CW with 1500 
VDC
adjustable, and 300 VDC fixed for the screens from a separate supply, 
and -40 to 55
VDC on the grids. I try to keep the output down to 400 watts by limiting the 
drive.
The drive level is right around 3.5 watts on CW or SSB. In AM mode I run the
rig at 1250 VDC plate volts, and modulate the plates, amp is class "C" at 
that time.

I dump a lot of air through the tubes, and maintain a close watch on the 
filament
voltage to the tubes, recommended is 6.0 VAC at this freq. You can get a lot
of good AM out of them that way.

It is also a good idea to have lots of metering to see when things start 
changing as
the parameters change during long transmissions. I monitor the grids and 
screens as well
as separate plate meters. The power should be reduced for 4X150A type tubes.

YMMV
Jim
WB2FCN

----- Original Message ----- 
From: "rayfri" <rayfri at highstream.net>
To: "Glen Zook" <gzook at yahoo.com>
Cc: <boatanchors at mailman.qth.net>
Sent: Monday, January 02, 2006 8:21 PM
Subject: Re: [Boatanchors] Gonset 972A

> 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....
>>
>>
>>
>>
>>
>>
>>Glen, K9STH
>>
>>Web sites
>>
>>http://home.comcast.net/~k9sth
>>http://home.comcast.net/~zcomco
>>
>>
>>
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>
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