[Amps] SB220 step start blows fuses

Gary Schafer garyschafer at largeriver.net
Sun Jul 9 23:20:21 EDT 2017

You don't have a big enough bulb.

I use two 300 watt bulbs in parallel. 300 watt bulbs are about the largest
you can find easily.

I made up the bulb unit using a square electrical box and mounted two
outdoor light sockets on it, an outlet and a regular house switch to short
out the bulbs when I want to bypass the series bulbs.
It works great for checking amps. It is really nice if you have an
intermittent arc or want to let suspect capacitors cook for awhile with the
amp is in standby as no harm is done if something arcs, the bulbs just light
up bright.

I sometimes plug the light bulb setup into a variac too. 


Gary  K4FMX

> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Warren Volz
> Sent: Sunday, July 09, 2017 9:53 PM
> To: amps; gudguyham at aol.com
> Subject: Re: [Amps] SB220 step start blows fuses
> I may shortly be looking to purchase a variac.
> After building a dim bulb tester this weekend I have a minor update.
> With 120V connected, the HV primary disconnected and one tube in a
> socket (doesn't matter which I use) the 100W bulb in my tester lights up
> bright. No fan and the meter lights aren't on. If I take out the tube
> the fan and meter lights work. So I guess I have a shorted tube? Would
> it be good to double check the DC/AC voltage on the filament supply with
> the tubes plugged in? That would show any sags that might exist.
> -Warren
> > On Jul 7, 2017, at 12:58 PM, gudguyham--- via Amps
> <amps at contesting.com> wrote:
> >
> > I know I sound like a broken record but yes, a Variac is the way to
> go.  Especially with amps that can have power supply problems and gassy
> tubes.  You will hear the plate transformer groan and won't see HV
> climbing on the meter if there is a problem in the PS long before the
> smoke Genie appears.  My Variac gets used daily several times after
> doing ANY work on an amp.  It's saved me loads of time fixing blown
> parts that would normally occur if I had just turned an amp on with
> problems.  Best investment I ever made.  0-250 volts at 20 amps.
> >
> > Sent from AOL Mobile Mail
> >
> >
> > -----Original Message-----
> > From: Bill Turner <dezrat at outlook.com>
> > To: Amps group <amps at contesting.com>
> > Sent: Fri, Jul 7, 2017 12:34 PM
> > Subject: Re: [Amps] SB220 step start blows fuses
> >
> >
> > ------------ ORIGINAL MESSAGE ------------(may be snipped)
> >
> > On Fri, 7 Jul 2017 10:21:36 -0400, Mark B. wrote:
> >
> >> A variac varies voltage.   It is not designed to limit current.
> >
> > REPLY:
> >
> > At the very low end of its range, a Variac limits current just fine. I
> > worked as a calibration technician at Tektronix for years, taking
> > brand new scopes off the assembly line and powering them up for the
> > first time. Believe me, a Variac is the only way to go with a unit
> > which could have any number of problems at first. Over the years I
> > powered up literally thousands of scopes this way and never a problem
> > with current limiting.
> >
> > 73, Bill W6WRT
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