[Amps] SB220 step start blows fuses

donroden at hiwaay.net donroden at hiwaay.net
Tue Jul 11 11:10:47 EDT 2017

The problem with this approach is that with two 60-100 watt bulbs *IN SERIES*,
there is too much resistance to "wake up" the amp.

It's difficult enough to try to "fix" an amp over the internet, and  
even more difficult to publish a broad-stroke technique that applies  
to every amp or the technical experience of the owner.

Some amps, like the SB220  require straight 240 ( no requirement for a  
common 120 return ), but others do. Some amps like the Collins 30S-1  
use switches to control the filament and HV relays.  The light bulb  
technique won't work well on these amps until you use a high enough  
wattage bulb to pull in the relays.  Study the schematics and  
accommodate  accordingly.

For a 2340vac amp, I would use a single 150 watt bulb in series and if  
it popped..... no big deal.
But I would know that there was a serious problem, and that I probably  
saved an unobtanium switch on the front panel.  But that's just me.   
You may have a better idea, and if that works for you ...great.   Do  
what is within your experience level and test equipment on hand and  
learn from your troubleshooting.


Quoting Jim Thomson <jim.thom at telus.net>:

> Date: Mon, 10 Jul 2017 12:41:52 -0500
> From: "Gary Schafer" <garyschafer at largeriver.net>
> To: "'Joe'" <nss at mwt.net>, <amps at contesting.com>
> Subject: Re: [Amps] SB220 step start blows fuses
> Well, yes you would need a bulb in each side of the 220 circuit or two bulbs
> in series (rather than parallel) on one side,
> assuming that the amp is not a 4 wire amp that also uses 120 volts.
> If something in the amp shorts you would have 220 volts across a single bulb
> and the bulb would burn out.
> 73
> Gary  K4FMX
> ##  agreed.  This is also why, if you install a separate fuse in  
> each leg of the 240 line,
> each fuse has to be rated for 240 vac.  IE:  if only one fuse blows  
> open, you will
> have 240 vac sitting across the same open fuse.
> ##  Step start should consist of one resistor, or 2 in parallel,  in  
> just one leg of the
> 240 line.   Ditto if the amp is wired for 120 vac, step star goes  
> into the hot leg of the
> 120 vac line.
> ##  The drake amps used a separate breaker in each leg of the 240  
> line.  They too have to
> each be rated for 240 vac.   Same deal, if only one breaker opened   
> off, you have 240 vac
> sitting across the open breaker.
> Jim  VE7RF
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