[Amps] Question re GU-74B grid current

[Carl]

I sure hope its not Class B Paul; more likely AB2 if there is some small 
amount of Ig on peaks.
There is also over 500W of idle dissipation per tube in order to make some 
attempt at decent IMD and that 3 stage bias can be heard on the air but not 
as bad as Alphas early attempts

Carl
KM1H


----- Original Message ----- 
From: "Paul Christensen" <w9ac at arrl.net>
To: <Amps at contesting.com>
Sent: Monday, October 22, 2012 3:18 PM
Subject: Re: [Amps] Question re GU-74B grid current


> Val,
>
> For the sake of completeness, I believe the typical "three state" bias 
> voltages for the ACOM 2000A (GU74B) are as follows:
>
> -124V on standby;
> -75V during plate idling with PTT key line enabled; and
> -52V when input RF is sensed.
>
> When using VOX, the amp is quickly transitioning from Class C to Class 
> .  -124V at level 1 should represent Class C.  I'll stand corrected if 
> it's not.
>
> Paul, W9AC
>
>
> ----- Original Message ----- 
> From: "Val" <val at vip.bg>
> To: <Amps at contesting.com>
> Sent: Monday, October 22, 2012 3:10 PM
> Subject: Re: [Amps] Question re GU-74B grid current
>
>
>> Jim,
>>
>> ACOM1000 and ACOM2000A are without doubt the most popular amplifiers 
>> based on GU74B. Many thousands of them are working under the following 
>> conditions at1000W output:
>> Plate  2350-2400V
>> Screen 340V
>> Anode current 510-580mA
>> Bias between -45 and -65V for 220 mA idling current (the EBS keeps the 
>> bias between -65 and -75V for idling current of 70 mA when no RF drive)
>> Normally the grid current is well below 10mA where the grid protection 
>> trips.
>>
>> 73, Val LZ1VB
>>
>>
>>> Could somebody advise me as to the resting plate current and operating 
>>> ctrl
>>> grid bias voltage they are using on a GU-74B (plate voltage is 2500V, 
>>> screen
>>> grid 300V)? Also, does the tube draw grid current? I realize that in 
>>> AB1, no
>>> grid current should be drawn, but the tube characteristic curves predict
>>> about 15mA grid current at full output (1000W output, 600mA anode 
>>> current
>>> (per tube) and 250W resting dissipation. I am interesting in what 
>>> builders
>>> are actually getting, and not information from data or spec sheets.
>>>
>>> Tnx and 73,
>>>
>>> Jim W8ZR
>>>
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>>
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