What happens to the bias voltage in the TX position with tubes out? Bad
zener or insulator?
Carl
KM1H
----- Original Message -----
From: <Gudguyham@aol.com>
To: <amps@contesting.com>
Sent: Tuesday, September 16, 2008 2:02 AM
Subject: [Amps] SB-220 PROBLEM
> Just when you thought you have seen just about every problem with a
> particular amp, you see a new one that baffles. In this case the
> problem is this.
> Amp blows the .82 grid shunt resistor. Replace resistor with new
> one. As a
> precaution after the repair attempt to bring amp up on a variac. As
> soon as
> the input voltage is raised on the variac, the plate meter indicates
> a reading
> and at the same time, the grid current goes negative when the
> multimeter is
> in grid position.
>
> Troubleshooting notes:
> 1. Removed tubes.....same thing
> 2. Isolated power supply from all metering circuitry, DC voltage OK
> 3. Checked 3600 ohm series plate current meter resistor....OK
> 4. Checked 1 ohm plate meter shunt resistor....OK
> 5. Replaced .82 grid shunt resistor....Ok
> 6. Meters themselves test OK
> 7. Removed 120 vdc bias supply voltage.....same thing
> 8. Shut down primary voltage to filament transformer....same thing
> 9. Isolated power transformer checked secondary AC...OK
> 10. Removed rectifier board checked for solder bridges etc...All OK
>
> SO I have checked just about damn thing and still same problem. The
> power
> supply is operating fine as I did isolate it from the metering
> circuitry and
> it is working OK as soon as I connect the metering circuitry the
> plate meter
> indicates a reading with only a few primary volts coming from variac.
> Don't
> know where to look next as I checked everything already. What have I
> missed?
> Suggestions? Lou
>
>
>
> **************Psssst...Have you heard the news? There's a new fashion
> blog,
> plus the latest fall trends and hair styles at StyleList.com.
> (http://www.stylelist.com/trends?ncid=aolsty00050000000014)
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|