Kinda OT: Swan Mark I Linear expected output on 4-400A's in G-G?

[Keith Rowland]

First question:  How are you able to use the 4-400, which is a tetrode, in place
of the 3-400Z, which is a triode?  The 4-400 socket diagram is 4BK, while the
3-400Z socket diagram is Fig. 3 (in the ARRL Handbook tube section).

In any case, here are the operating parameters for the 4-400 in Grounded Grid
configuration (all figures are for a single tube):

Plate Dissipation:  400 watts (Forced air cooling required)
Max. plate voltage:  4000 volts
Screen Dissipation (max):  35 watts
Max. Screen Voltage:  600 volts
Full ratings to 110 mHz
For grounded grid operation:
Plate Voltage:  2500
Screen:  0 (control grid and screen grid tied together, making it in effect a
triode)
Plate current:  80-270 ma. (single tone)
Grid voltage:  0  Grid current, single tone:  100 ma.
Screen current:  55 ma. (single tone)
Single-tone driving power:  38 watts (single tone)
Output power (single tone):  325 watts

Anyway, regardless of how it's happening, with the above parameters and two tubes,
the expected output power is just what you are getting:  650 watts.

Keith





"Bob, WB2UJD" wrote:

> OK you amplifier gurus,
>
> I have a Swan Mark I I have restored to mint condition and I am using 2
> 4-400A's in G-G in place of the 3-400Z's (3-500Z predecessor) it was designed
> for.  It seems to work pretty well, but I am not sure it works as well as it
> might.
>
> What might I expect as a reasonable power output from such a combination?
> Here are a few pertinent details:
>
> 3.75 MHz, just over 650W out with about 112W drive (not 100% sure of the
> HM-102 meter cal)
> The Mark I has an untuned cathode driven input.
> 2600V key down, 3300V idling, in operate (SSB) position
> 240 mA plate current
> 540 mA grid current (yes this is high, but tetrodes in G-G tend to do this)
> 90 mA grid current idling (bias)
> Not 100% sure of metering cal either, but all metering resistors have been
> replaced and are 1% or better.
>
> DC plate input comes out as 624W.  Not sure how to calculate the grid portion
> or if this contributes to total DC input, probably does in some fashion.
>
> In Tune/CW position:
> 3.75 MHz, about 450W out with about 112W drive
> 1600V key down, 1900V idling
> 300 mA plate current
> 500 mA grid current
> 55 mA grid current idling (bias)
>
> DC plate input comes out as 480W.
>
> I am looking for some idea of how the amp is doing and what might be expected
> of such an amp (Or how likely I am to piss people off if I were to attempt to
> use this amp on SSB!).  This is my first linear in close to 30 years as a ham!
>
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