Metropoulos Forum

Went to bias up my Splawn Quickrod, that I bought used about a month ago, with new KT77's and I get no mA reading on Power tube socket V4. V5,6,7 all show readings but 4 does not. No visual signs of damage, (I am a bit of a noob) for whatever that's worth. Any suggestions as to what to check and how would be greatly appreciated.

Check the screen grid resistor to make sure it isn't burned open.

Check the tube first, the screen grid can kill you.

axeman wrote:Check the tube first, the screen grid can kill you.

good point. swap the tubes and see if the problem stays with the socket or follows the tube. If it stays with the socket, (take all of the usual safety precautions for neutralizing the amp and discharging the caps) and then check the screen grid resistor to see if its an open circuit.

I moved the tubes around and it still does it. So it's not the tubes.

I just checked Plate voltage at that socket and it's there (498).

I checked continunity at pin 8 and it checked OK.

I also checked for negative grid voltage on Pin 5 and it reads correct.

danosol wrote:I just checked Plate voltage at that socket and it's there (498).

I checked continunity at pin 8 and it checked OK.

I also checked for negative grid voltage on Pin 5 and it reads correct.

What does the screen grid resistor measure with no tube in the socket? You might want to check all of them just to be sure of the values. If they all check out good, you might want to check the voltages (with the tubes in) at pin 4 and 5 on each tube. Pin 4 is the screen grid.

Just checked to see if there was any continunity on the screen resistor and it measured 0. V5, V6, and V7 all measured 750Ohms. Looks like that is the problem.