Hi Mike
The dual 8877 arrangement should cost more as it allows more dissipation.
Watt for watt the 800's will cost more, more sockets more room. The lower
plate voltage means lower RL which means MORE required tune capacitance and
lower tank inductance,(smaller). You can maintain a lower loaded Q with the
same Cout+Cstray using the lower plate voltage. By the time you match the
dissipation of the dual 8877's with the 800's (four tubes) you have about
the same total Cout+Cstray, still not much benefit for 28mhz. I would think
the reason one doesn't see many of these large amps is that they can't be
type accepted for amateur radio in the US, although the "export only" amps
are freely sold here. Without the commercial market for these big non type
accepted amps (as Henry has) it might be hard make them profitable legally.
Paul
PAUL HEWITT
WD7S PRODUCTIONS
QRO HOMEBREW COMPONENTS
http://wd7s.home.att.net
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
> Behalf Of Mike McCarthy, W1NR
> Sent: Saturday, February 28, 2004 6:26 AM
> To: P. Coppin; Amps@contesting.com
> Subject: RE: [Amps] 2 x 8877
>
>
> The Alpha SX had issues on 10M because of the capacitance of the two
> tubes. Also, 2x8877 is more expensive than 3x3cx800. With the 3cx800,
> the plate voltage is lower, required capacitance is lower, voltage
> ratings of tank components is lower translating into a more cost
> effective design.
>
> Still, nothing impresses me more, at least visually, than a pair of
> 4-1000's built into a cabinet with windows...
>
> Mike, W1NR
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
> Behalf Of P. Coppin
> Sent: Friday, February 27, 2004 8:29 AM
> To: Amps@contesting.com
> Subject: [Amps] 2 x 8877
>
>
>
> First of all, sorry for my poor english.
>
> I would like to know the reason why the amps manifacturers build linear
> amps
> using three 3cx800a7, 2 3cx1200a7, one 3cx3000a7 and ruskies but no one
> build a linear amplifire with 2 3cx1500a7 (8877) such as the Alpha sx.
> What problems they could have ?
>
> 73
> Paul i8ixo
>
>
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