1-01-02 10.50, skrev Peter Chadwick på Peter_Chadwick@mitel.com följande:
>
> Rich says:
>
>> With a 4-250A or 4-400A, it takes c. 75mA of ZSAC
>> for good linearity. In order to obtain 75mA of ZSAC
>> with 0v bias, one needs c. 3500v.
>
> Even then, you're pushing things to get more than about 400 watts out with
> reasonable linearity. In fact, nearer 4kV is better.
>
> 73
>
> Peter G3RZP
>
>
>
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>
Interesting Peter.
I took a quick glance in my library and found a 2x4-400 amp in the 1981 ARRL
Handbook with both grids grounded. At the 2kW level with 3.4kV they say
120mA idling current, 588mA plate current and the grid current was around
200mA. Drive power was around 100 watts. This is of, course, with two tubes.
The tube was manufactured by several European firms. SIEMENS = RS 1002.
MULLARD = QY 4-400. PHILIPS = QB 4/1100. TELEFUNKEN = RS 686. NATO = CV
3879.
As for distorsion, I see in a MULLARD news letter 40 db below one of the
test tones at 4 kV plate voltage, 700 G2 voltage and 498 watts at the load.
These ratings are for good linearity with a slightly higher no signal idling
current and lower effiency - class AB1 grounded cathode - 85 mA idling
current.
As far as I remember these tubes have graphite anodes, are cheap surplus as
they are used in AM broadcast transmitters and have the same filament
requirements as and can directly replace the 3-500Z or 3-400Z. However, I
assume stability may be affected and one has to replace the parasitic
chokes, eventually?
Has anyone seen any distorsioin measuements on the 4-400 in high mu gg?
One can also use 4-250A or 4-125A that have a lower anode dissipation.
The 4-1000A in the same family ( yes Rich) with another socket, can also be
used in the same way instead of a 3-1000Z. According to Bill W6SAIs RADIO
HANDBOOK the following applies to the 4-1000A: At 3.5kV and at the 2kW level
the anode impedance is 3000 ohms - resting no signal current is 110 mA -
anode current is 650 mA single tone - G1+G2 grid current is 230 mA - drive
power 110 watts. 1.5A higher filament current than the 3-1000Z otherwise the
same filament requirements as the 3-1000Z.
EIMAC has recommended the 4-1000A in high mu gg in one of their application
notes.
Prosit de Hans SM5KI
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