> 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 ?
>
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