[Boatanchors] Gonset 972A

[rayfri]

And on FM???


James M. Walker wrote:

> 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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>> ** List Administrator - Duane Fischer, W8DBF/W9WZE **   ** For 
>> Assistance: dfischer at usol.com **         $$ For vintage radio info, 
>> see the HCI web site $$      http://www.w9wze.org
>>
>>
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