[Amps] SB220 step start blows fuses
jim.thom at telus.net
Fri Jul 7 12:23:06 EDT 2017
Date: Fri, 7 Jul 2017 01:07:36 +0000
From: Bill Turner <dezrat at outlook.com>
To: Amps group <amps at contesting.com>
Subject: Re: [Amps] SB220 step start blows fuses
<Because of all the above, IMO, a better way is to use a Variac to
<slowly bring up the voltage while monitoring the current. Variacs are
<widely available on eBay. Every ham shack should have one.
<73, Bill W6WRT
### be careful with any variac rating. The small 0-120 vac or 0-132 vac...at
1.2 amp types, typ 3 inch diam x 2 inches thick, are only rated at 157 va..and thats
based on 132 v X 1.2 A. The tubes alone will suck 150 VA. If careful, you could
test the HV portion of the supply, with tubes removed.
## To use the varaic, you really need a 5A or larger variac, if using a 0-120 or 0-132
V type. You also need to temp disconnect the entire step start assy..and feed the output
of the variac directly into the 120 vac input of the plate xfmr. IF the step start assy is included
in the mix, and low voltage on the varaics output....step start relay will not pull in, and step start
resistor is still in the circuit, and you will probably end up with a blown step start fuse.
## with step step assy temp out of the circuit.....and starting with the variac on zero, + a safety
fuse on the input of the variac, + both either both tubes removed from sockets, or anode leads
temp dis connected... then bring the variac up real slow. If u have any fubar in there, the small
1-3 A safety fuse on the input of the variac will open up. Removing tubes from sockets will eliminate
the 150 va fil load.
## If fuse blows open, disconnect the 8 filter caps + doubler diode board...leaving just the xfmr, with
nothing connected to sec of plate xfmr. Try again, if good, add in the doubler diodes, then re-test, then
evaluate. If good, add in the 8 x caps, then re-evaluate. Its really just a simple process of elimination.
## Once the B+ supply is working correctly... ok, remove variac, add the step start assy to the mix...then evaluate.
If good, then install both tubes...one at a time.
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