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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: Tue, 11 Jul 2017 18:35:19 -0600
List-post: <>
Again thank you all for the advice and guidance. 

Replacement fuses showed up today so I'm being a little more
adventurous. As multiple people pointed out the dim bulb tester I have
as built won't work unless I can find at least one 300W bulb. 

So, I remove the dim bulb tester and tried each tube in the amp. Good
news is that both filaments light up just fine! To me that rules out the
filament supply and paints a target on the HV supply as many of you have

The amp as I received it was a pile of parts, and so I have no reference
in terms of working/not working prior to my mods. Both the QSK and the
RM220 were used pulls off of an auction site. The RM220 is squarely in
my sight now since it had a burned out metering resistor when I got it.
When I checked previously the diodes were all ok. Also, all components
(caps + resistors) on the filtering board are new. 

I'll likely try reconnecting the HV primary without the plates connected
to see what that does next. 


On 07/09/2017 8:52 pm, Warren Volz wrote:

> 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.
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