[Amps] Multi-tube vs Single or Dual-tube amps?

[Joe Subich, W4TV]

> Filament require high current capability, tank circuits become more
> complex because of the change in load impedance,

Filament current requirements are generally proportional to the peak
current capability of the tube.  Multiple low power tubes will often
require as much total current as a single tube of the combined power
capability.

Tank circuits will, again, generally be similar for a given power
output, particularly if the plate voltage for a single high power
tube is the same as multiple lower power tubes.

The biggest problem with multiple tubes is the higher grid-plate
capacitance (output capacitance in GG amplifiers) which results in
higher tank circuit Q, greater losses, and increased instability
at higher frequencies.  In addition, multiple (> 2) tubes often
create layout issues and difficulties maintaining balance in the
input/output connections.

73,

    ... Joe, W4TV


On 2015-01-19 4:36 PM, Roger wrote:
> It becomes a lot more complex when you start adding tubes. Power supplies,
> in particular HV and Filament require high current capability, tank
> circuits become more complex because of the change in load impedance, input
> tuning circuits get a bit more complicated plus the need to have the
> capability of adjusting bias and monitoring each tube individually. I could
> probably go on but I think you get the picture.
>
>
> 73, Roger
> AI7RR
>
> On Mon, Jan 19, 2015 at 1:27 PM, qrv at kd4e.com <qrv at kd4e.com> wrote:
>
>>  From time to time a multi-tube amp shows up, such designs were
>> common with sweep tubes, I think some with 4x150's, and 6146's.
>>
>> Other than the added sockets and wiring complexity are there
>> additional down-sides to such a design?
>>
>> e.g. Eight 6146's should generate 600w 160-10m and are cheap.
>>
>> Just pondering ...
>>
>>
>> --
>>
>> *David*
>> ~KD4E~
>> Nevils, Georgia USA
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