> I think you missed the point I was making.
No, I didn't miss the point. Running an amplifier in
a mis-tuned condition (tune for 1500 W Output and drive
to 800 W Out) is hazardous and inefficient. If you
tune the amplifier for 800 W at the higher plate voltage
the Q of the pi network soars resulting in all kinds of
problems.
Instead, if you reduce the plate voltage 30% - 40%,
leave the bias up so the tube is running with no idle
current (class B), and dive it to the correct half
power (700-800 W out) level, the PLI will be correct
for the design of the pi network. Circulating current
will be reduced and efficiency will increase.
> -----Original Message-----
> From: gudguyham@aol.com [mailto:gudguyham@aol.com]
> Sent: Saturday, August 29, 2009 12:10 PM
> To: lists@subich.com; amps@contesting.com
> Subject: Re: [Amps] SB-220 bias question
>
>
>
>
> The SB-220 will not survive RTTY operation in "full smoke"
>
> @@@@@ Agreed, for sure, but the AAL-80, AL-82 et al. do not
> change the plate voltage on any mode. The operator is told
> to adjust power output according to the mode. I NEVER said
> to rum the SB-220 at full smoke on RTTY. My whole point is
> to run the tubes at higher plate voltage with less plarte and
> grid current for the same power output. Naturally on must be
> prudent with thr SB-220 as with the AL-80/ Al-82 et al. I
> think you missed the point I was making. Lou
>
> -----Original Message-----
> From: Joe Subich, W4TV <lists@subich.com>
> To: gudguyham@aol.com; km1h@jeremy.mv.com; amps@contesting.com
> Sent: Sat, Aug 29, 2009 11:33 am
> Subject: Re: [Amps] SB-220 bias question
>
>
>
>
> > So in other words it's not a technical issue so much as it is
> > a "idiot proof" fail safe measure?
>
> No. The SB-220 will not survive RTTY operation in "full smoke"
> mode. 100% duty cycle at 1500 W output will cook both the
> transformer and the output. Running at lower power keeps the
> transformer and pi-network within ratings and doing so at the
> lower voltage setting keeps correct plate load impedance.
>
> Remember, the SB-220 was designed for 1 KW DC (average) input
> power. That it will handle 1500 W PEP output with reasonable
> duty cycles is a testament to the care that went into the design.
> Still, it is no Alpha or Henry and will self destruct if pushed
> to 1500 W CW "brick on the key" output (approximately 2500 W DC
> input).
>
> 73,
>
> ... Joe, W4TV
>
>
>
> > -----Original Message-----
> > From: amps-bounces@contesting.com
> > [mailto:amps-bounces@contesting.com] On Behalf Of gudguyham@aol.com
> > Sent: Saturday, August 29, 2009 10:35 AM
> > To: km1h@jeremy.mv.com; amps@contesting.com
> > Subject: Re: [Amps] SB-220 bias question
> >
> >
> > So in other words it's not a technical issue so much as it is
> > a "idiot proof" fail safe measure?
> >
> > Many operate the SB-220 on RTTY and digi modes where the CW
> > position is a key to transformer survivability.? ? The same
> > for 12/17M where the tank circuits are far from optimum and
> > bandswitch arcing can occur at 1200W.? ? Some owners are a
> > bit slow in tuning up and the CW position reduces the plates
> > from brilliant orange to a darker version.? ? Carl? KM1H?
> >
> >
> >
> >
> > -----Original Message-----
> > From: Carl <km1h@jeremy.mv.com>
> > To: Gudguyham@aol.com; amps@contesting.com
> > Sent: Sat, Aug 29, 2009 9:00 am
> > Subject: Re: [Amps] SB-220 bias question
> >
> >
> > Many operate the SB-220 on RTTY and digi modes where the CW
> > position is a key to transformer survivability.? ? The same
> > for 12/17M where the tank circuits are far from optimum and
> > bandswitch arcing can occur at 1200W.? ? Some owners are a
> > bit slow in tuning up and the CW position reduces the plates
> > from brilliant orange to a darker version.? ? Carl? KM1H? ? ?
> > ----- Original Message ----- From: <Gudguyham@aol.com>?
> > To: <amps@contesting.com>?
> > Sent: Saturday, August 29, 2009 7:09 AM?
> > Subject: [Amps] SB-220 bias question?
> > ?
> > > It was always my understanding with the SB-220 and other
> older amps
> > > that? the reason for lowering the plate voltage on the 3-500's or
> > > whatever tube,? was to comply with FCC regulations. Years
> > ago the rule
> > > was 1KW DC input > CW? and 2KW PEP input SSB hence the
> > change in plate
> > > voltage. Now that this > rule? has changed I was
> thinking. It is my
> > > observation that the 3-500 tube? performs much better
> with 3000 or
> > > more plate voltage, tube makes nice > power? with lower
> > grid current
> > > for the same power at a lower plate voltage. > Hence,? my idea.? I
> > > routinely use 7 1N5408 reversed diodes to replace blown zeners.?
> > > Expanding on that idea I was thinking of removing the power
> > > transformer > primary? windings from the CW/SSB switch and wire
> > > nutting the wires together that? produce the higher plate
> voltage,
> > > then making up a small perf board with? about (have to
> > experiment) 11
> > > diodes and using the CW/SSB switch to short > out 4? of the
> > diodes on
> > > CW to lower the idle current and have normal SSB idle?
> current when
> > > switched to SSB. That has been the modern day approach to >
> > this? on
> > > the newer amps since the FCC ruling has changed. Many
> hams I know >
> > > went? to running CW with an SB-220 and other older amps
> in the SSB
> > > mode anyway.? Thoughts? 73 lou?
> > > _______________________________________________?
> > > Amps mailing list?
> > > Amps@contesting.com?
> > > http://lists.contesting.com/mailman/listinfo/amps ?
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
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