[Amps] Question re GU-74B grid current

[Leigh Turner]

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