Rephrasing:
An amp should be tuned up AT the power level it's going to run, OR a
"tune" switch that gives less plate voltage but the amp is tuned up at
the same ratio of plate current to plate voltage it will run in the high
position. IOW some amps like my Alpha can be tuned up at reduced power
and then switched to high power for SSP and the Q will be correct for
the much higher PEP. For amps that have very poor PS regulation it's
almost essential to tune in the TUNE position (if they have one) because
the plate voltage under a steady load in tune up is much less than with
SSB and would result in a mistuned condition. For amps being run at
reduced power they should be tuned up at that power level. I hope I
phrased all that correctly.
73
Roger (K8RI)
Joe Subich, W4TV wrote:
>> 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 ?
>>>>
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