[Amps] SB-220 bias question

[gudguyham at aol.com]

 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 at subich.com>
To: gudguyham at aol.com; km1h at jeremy.mv.com; amps at 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 at contesting.com 
> [mailto:amps-bounces at contesting.com] On Behalf Of gudguyham at aol.com
> Sent: Saturday, August 29, 2009 10:35 AM
> To: km1h at jeremy.mv.com; amps at 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 at jeremy.mv.com>
> To: Gudguyham at aol.com; amps at 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 plate
s 
> from brilliant orange to a darker version.? ? Carl? KM1H? ? ?
> ----- Original Message ----- From: <Gudguyham at aol.com>?
> To: <amps at 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 at contesting.com?
> > http://lists.contesting.com/mailman/listinfo/amps ?
> 
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