On 1/19/2015 5:25 PM, Peter Voelpel wrote:
The design needs to take into consideration the characteristics of the
tube(s) and allow for such, In the case of the Emtron DX-2so ans DX-3sp
the bias is set for each tube individually. The closer the tubes are
matched, the lower the IM products. That something most of the multi
tube amps using sweep tube did not address. Many of those old designes
had pretty poor IM products
So, you have the question of how close to each other are the basic tubes
matched and will adjusting the bias individually be good enough? The
4CX1500B and the Chinese FU728F have excellent IM characteristics and
differences can be taken care of with the individual bias adjustments.
BUT they are high gain Tetrodes and require little drive, which means
dialing back the output of the exciter. If this is done in the exciter
using its ALC each transmission, or even each transmission "may" have a
leading edge, full power pulse while the ALC is being developed to limit
the power. These can lead to the pulses over driving the amp creating
splatter. Already mentioned are the low impedance of the input and out
put circuits when using multiple tubes and matching multiple tubes along
with the additional power to light the fire. Lower voltage, but higher
current takes a slightly larger transformer.
Another downside is the additional area required for the tubes as well
as enough and equal cooling to each tube.
I would no longer call 6146s cheap if purchasing new.<:-))
Multiple tubes "usually" means smaller tubes, which means a more compact
amp, but the power supply needs to be capable of delivering the desired
voltage and current, but the PS can be remote. Then its size may be a
non issue.
The problem with legal limit (and beyond) single tube amps is that most
of the tubes are BIG! Too bad the 3CX3000 series can not be mounted
horizontally. Allowing for the tube height plus clearance above and
below makes for a cabinet of substantial size.
73
Roger (K8RI)
I guess a 813 or 4-125 is cheaper
73
Peter
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of qrv@kd4e.com
Sent: Montag, 19. Januar 2015 22:28
To: amps@contesting.com
Subject: [Amps] Multi-tube vs Single or Dual-tube amps?
>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 ...
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