Heathkit SB-220

[Radio Tech]

Amp blows the .82 ohm resistor.
Is there anything other than a gassey tube that would cause this to blow?
The zener checks ok. Think I am going to replace the metering.rectifier board with the harbach board.

Any suggestions are welcome.

BTW, Drake L4B came in this week end. the .82 is blowed in it lol.

 

[wavrider]

anode short under high voltage. I got a triode in the shack that does the same thing, filament lights up but as soon as HV is applied it blows the circuit.

 

[Clayton]

Usually the filament will break a strand and it will rest on the grid. This can kill the amp
in many ways. Now, there is a fix! Remove the tube and carefully lay it in it's side and prevent it from rolling on the bench with wedges. I use solder to wrap both filament pins together, then do the same for the 3 grip pins. Now hook up a variac, one lead to the grid and the other to the filament. SLOWLY increase the voltage until you see a flash. This will burn away the short and the tube will now work as it should.

I have done this to several tubes of this type with very good results. Learned this trick from an guy that used to work at Eimac.

73 and good zapping
Clayton N4EV

 

[wavrider]

Clayton thanks I will give this a try, can't hurt as the tube is useless as it sits now.

 

[Radio Tech]

I ordered the harbach rectifier/metering board and solved the problem in this one.

 

[wavrider]

Glad to hear that you got it up and running.

I tried the filament and grid with variac as mentioned before. I saw no flash?

 

[Crusher]

More than likely its the tube, but you might get lucky and just have it be the bypass cap or the blocking cap.