[Amps] Question re GU-74B grid current

[Carl]

Yeah sure. A 600W rated tube fraudently labled 800W to grab US dollars. At 
least ACOM has erased the GU74B for a 4CX800A even tho running them just as 
hard.

They will soon go the way of the dodo bird unless the Chinese copy and maybe 
improve it.

Carl
KM1H



----- Original Message ----- 
From: "Leigh Turner" <invertech at frontierisp.net.au>
To: <amps at contesting.com>
Sent: Monday, October 22, 2012 9:28 PM
Subject: Re: [Amps] Question re GU-74B grid current


>
> Yes, the ACOM-1000 and ACOM-2000A are two good examples of what good amp
> designers can do with good tubes.  These GU74B tube based amplifier 
> products
> have been immensely successful for ACOM and others.
>
> Jim you are absolutely right to be interested in what amp builders are
> actually getting and experiencing from these fine tubes, rather than rely
> only on information gleaned from the translated GU74B Russian data/spec
> sheets. Unlike the savvy folk, many are not aware of the full picture in
> respect of how good these conservatively rated mil-spec tubes actually 
> are.
>
> Leigh
> VK5KLT
>
>
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Carl
> Sent: Tuesday, 23 October 2012 11:19 AM
> To: Vic K2VCO; amps at contesting.com
> Subject: Re: [Amps] Question re GU-74B grid current
>
>
> Thats being rather polite about it (-;
>
> Carl
> KM1H
>
>
>
>> 71% overall efficiency is remarkable for a class AB1 amplifier.
>
>
>> On 10/22/2012 12:10 PM, Val wrote:
>>> 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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