OK, I've received the education I anticipated, thanks!
Price comparison for a true 600w output 160-10m linear amp:
813 $90. new, $45 - $50. each used, tested good.
x 2 = $90. - $180. tube cost.
6146 $15 - $30. nos, $10. - $20., used tested good.
x 8 = $80. - $240. tube cost.
So, unless one had a box of cheap 6146's, a dual-813 amp would
make more sense.
I get that one might force a true 600w out of a single 813, e.g.
http://www.iw5edi.com/technical-articles/a-low-cost-600-watt-ultra-linear-amplifier
but that seems a bit aggressive for the life of
the tube - and appears to limit band coverage as well.
One might also force 600w out of six, rather than eight, 6146's,
but the same caveats appear to apply.
Yes?
Thanks - David
> 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
>>
>> >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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