[Amps] SB220 Meter blown
jim.thom at telus.net
Fri May 15 12:13:44 EDT 2020
Date: Fri, 15 May 2020 11:10:06 -0400
From: Artek Manuals <Manuals at ArtekManuals.com>
To: "amps at Contesting.com" <amps at contesting.com>
Subject: [Amps] SB220 Meter blown
<I am resurrecting a SB220 that had an apparent classic Grid/plate short
<event. One of casualties appears to be the right hand meter movement.
<This is the one for Grid Current and HV. I am pretty far into it and the
<meter movement measures open , the internal shunt resistor is blackened
<( and open?)
<Anyone got a surplus movement from a parted out unit? Nothing found on
<evil-bay at the moment
## I believe harbach sells replacements. The heathkit shop might sell em.
Next time be sure to install rvs connected 6A10s or 1N5408s between
B- of hv power supply caps..... and chassis. HV fuse, followed by 50 ohm glitch resistor is series
## Toss all the grid chokes and caps. Bond each of the 3 x grid pins directly to chassis
## Install a 2nd HV fuse...in series with one leg of the plate xfmr secondary....either leg.
## Ok, now there is no way to blow anything up..including meters. Cro bar anything u want,nothing happens
except for a blown hv fuse.
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