[Amps] SB220 power supply

[Pat Barthelow]

Re the SB 220,

If you had a fine carbide drillbit, would it be possible to drill cleanly into the center region of the laminations of the transformer, without doing functional damage to the tranformer?
If you could, then,  slip a tiny, cylindrical RTD, or thermistor, to measure temperature?   I dont know the hardness or drillability, of the core laminations, so it might not be easy to drill....if you could place the sensor in the middle of the laminations, center of the windings, (which I would assume is the hottest spot) and  run the transformer hard ,  what would be a reasonable upper limit temperature to look for as a representative maximum running power/Duty cycle?

All the best,
Pat Barthelow    (916) 315-9271
aa6eg at hotmail.com
http://www.jamesburgdish.org
Project Manager,  Jamesburg Moonbounce Team


> From: km1h at jeremy.mv.com
> To: kk7uv at bresnan.net; amps at contesting.com
> Date: Sun, 2 Mar 2008 22:17:05 -0500
> Subject: Re: [Amps] SB220 power supply
> 
> Typical HV is 2500 @ 800 ma key down for 1100-1200W out on a stiff 240VAC 
> line.
> 
> They may not care for 48 hours of CW contesting in the SSB position but they 
> hold up very well otherwise.
> 
> I see no reason why four 813's cant be used in GG at the same power level.
> 
> Added filter capacity wont do anything for key down readings. It may give a 
> bit better SSB regulation; I use 330MF CDE 381LX caps as replacements in the 
> SB-220 as they fit the blocks perfectly.
> 
> Carl
> KM1H
> 
> 
> ----- Original Message ----- 
> From: "Steve Flood" <kk7uv at bresnan.net>
> To: <amps at contesting.com>
> Sent: Saturday, March 01, 2008 9:16 AM
> Subject: [Amps] SB220 power supply
> 
> 
> > To avoid having to build a separate power supply box, I am thinking of 
> > using an SB-220 transformer.  As I see it, it was meant to run a pair of 
> > 3-500's at about 2700volts and 700mA.   I am thinking of using it to run 
> > either three or four  813's.  My calcs show about 170 to 180mA per 813 in 
> > class B at 2700v, which tells me I am probably pushing the transformers 
> > capability with four 813's.
> >
> >  An additional concern is the voltage drop on key down.  I read an online 
> > article by K0GKD regarding the voltage drop and impact on linearity with 
> > Heaths stock 25uF of filter capacity.  He increased the filter capacity to 
> > 56uF and still noted a 10% voltage drop, but noted better regulation (??).
> >
> > If I end up with a voltage drop on key down or voice peaks, that tells me 
> > the plate current will rise and further tax the transformer.
> >
> > So, my thought is the SB220 tranny may work well for three 813's but maybe 
> > not with four 813s.
> >
> > Is my rationale correct?
> >
> > Steve, KK7UV
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> 
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