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Re: [Amps] SB220 step start blows fuses

To: amps <>,
Subject: Re: [Amps] SB220 step start blows fuses
From: Warren Volz <>
Date: Sun, 9 Jul 2017 20:52:40 -0600
List-post: <>
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.


> On Jul 7, 2017, at 12:58 PM, gudguyham--- via Amps <> 
> 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 <>
> To: Amps group <>
> 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. 
> 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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