[Amps] Question re GU-74B grid current

[Val]

Paul,

You are absolutely right. I omitted the standby state as I think that Jim 
doesn't care about it.

73, Val LZ1VB

----- Original Message ----- 
From: "Paul Christensen" <w9ac at arrl.net>
To: <Amps at contesting.com>
Sent: Monday, October 22, 2012 10:18 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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