[Heathkit] SB-220 Resistor # R3 Blown

[jeremy-ca]

Usual reasons:

1. Turning it on with cover off and shorting bar actuated
2. Tube short
3. Shorted bias zener

2 often caues 3 and takes out a grid choke.

Youre also lucky since the meter usually blows when the switch is in the 
grid current position. Solution: put reverse connected 1N4004-4007's across 
the meter terminals.

Carl
KM1H
Amplifier repairs, upgrades and 6M conversions since 1964
----- Original Message ----- 
From: <kc7hkp at comcast.net>
To: <heathkit at mailman.qth.net>
Sent: Tuesday, April 01, 2008 8:10 PM
Subject: [Heathkit] SB-220 Resistor # R3 Blown


> HI Guys
> I am bring a SB-220 Amp back to life, I put power to it with the tubes out 
> and meter showed 2700 volts.
> So i put the 2 Tubes  in  and resister R-3,  2 Watts at .82R had blown, 
> according Rich Measures page its the resistor grid current meter shunt 
> resistor and is the only path for the High Voltage to go to chassis from 
> the filter bank.
> Does any one know why it may have blown, ?
> It  has to do with the interlock also.
> easy to replace but why it broke is got me worried, i am not a Tech man so 
> i need some ones help here.
> Thanks
> George
>
> --
> KC7HKP
> George Yazzolino
> 14801 NE 20th Circle
> Vancouver, Wa. USA ,98684
> Grid CN-85
> kc7hkp at arrl.net
>