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Re: [Amps] SB220 step start blows fuses

Subject: Re: [Amps] SB220 step start blows fuses
Date: Tue, 11 Jul 2017 10:10:47 -0500
List-post: <>
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 <>:

Date: Mon, 10 Jul 2017 12:41:52 -0500
From: "Gary Schafer" <>
To: "'Joe'" <>, <>
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.

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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