Diagnosing bad 9-pin sockets

[ViperDoc]

I just powered up an 18-Watt build and I don’t have any voltages on V1. Furthermore, the tube doesn’t light up. The heaters both measure 3.2 VAC on pins 4-5 and 9, and each pin on the socket probes continuous from the socket side to each solder lug. I don’t see any debris inside any of the pin sockets. The tube is harder then normal to put in and take out. I’m extra careful to ensure I’m putting the tube in correctly and fully seated. When I trade tubes to rule out a bad tube, the non-lit V1 tube lights up in V2. I’m using Belton micalex sockets which are supposed to be excellent. I’m about to change the socket but thought I’d ask. Thanks.

I should add that there is no solder wicking from the lugs tonthe sockets, I made sure of that when I soldered them.

[Stevem]

Something is strange here, as your stating / posting that you can not measure any heater voltage on the stocker pins, yet you state what the voltage reading is that you have found there!
Is V2 also a 9 pin preamp tube wired the same and that's powering up?

If your powering with 6.3 volts then pins 4 and 5 need to be shorted to each other.

[sluckey]

the tube doesn’t light up. The heaters both measure 3.2 VAC on pins 4-5 and 9

That behavior can be caused by a bad socket. But it's more likely that one of the filament wires is broken or not making contact to the tube pin. You will still be able to measure 3.2v on each pin even if one of the filament wires is broken or completely missing. You need to measure voltage ***BETWEEN*** filament pins, ie, put one probe on pins 4/5 and the other probe on pin 9. You will measure 6.3v if both filament wires are OK.

[ViperDoc]

the tube doesn’t light up. The heaters both measure 3.2 VAC on pins 4-5 and 9

That behavior can be caused by a bad socket. But it's more likely that one of the filament wires is broken or not making contact to the tube pin. You will still be able to measure 3.2v on each pin even if one of the filament wires is broken or completely missing. You need to measure voltage ***BETWEEN*** filament pins, ie, put one probe on pins 4/5 and the other probe on pin 9. You will measure 6.3v if both filament wires are OK.

Bravo, sir. I will check that tonight!

[ViperDoc]

Something is strange here, as your stating / posting that you can not measure any heater voltage on the stocker pins, yet you state what the voltage reading is that you have found there!
Is V2 also a 9 pin preamp tube wired the same and that's powering up?

If your powering with 6.3 volts then pins 4 and 5 need to be shorted to each other.

The pins read hot, but the tube is not lit. pins 4-5 are indeed shorted together. Thanks.

[PaulD]

That behavior can be caused by a bad socket. But it's more likely that one of the filament wires is broken or not making contact to the tube pin. You will still be able to measure 3.2v on each pin even if one of the filament wires is broken or completely missing. You need to measure voltage ***BETWEEN*** filament pins, ie, put one probe on pins 4/5 and the other probe on pin 9. You will measure 6.3v if both filament wires are OK.

Assuming that the heater supply is functioning then measuring between heater pins will still read 6.3v regardless of whether the filaments are intact! The filaments can be checked for continuity with a multimeter (the cold resistance value will vary depending on the valve but a typical 12AX7 might read 10 - 40 ohms between pins 4 & 5 and half of that between 4/5 & 9).

If, as the OP says, the heater voltage is OK and the valve lights up when plugged into another socket then clearly the problem can only be the socket. A close examination with a magnifying glass will probably show the cause.

[sluckey]

What I said is true.

[PaulD]

What you said was "You need to measure voltage ***BETWEEN*** filament pins, ie, put one probe on pins 4/5 and the other probe on pin 9. You will measure 6.3v if both filament wires are OK"

You will also measure 6.3v if either or both filaments are not OK, it tells you nothing about the filaments.

[sluckey]

What you said was "You need to measure voltage ***BETWEEN*** filament pins, ie, put one probe on pins 4/5 and the other probe on pin 9. You will measure 6.3v if both filament wires are OK"

You will also measure 6.3v if either or both filaments are not OK, it tells you nothing about the filaments.

Exactly. Who cares about the filament since he already verified the tube will light up in the V2 hole.

My comment was directed to the fact that he did not measure the filament voltage correctly to verify that he did in fact have 6.3v to the socket. He has also ruled out the socket so that only leaves one of the wires in the filament string between V2 and V1 being open, either bad solder or broken wire.

[pompeiisneaks]

Also realize that some tubes heaters glow so little it almost requires a dark room to see them. But since you tried it in V2 and it glowed, something's definitely amiss. Can you push the multimeter down into the socket pin side of hte pins to ensure they're reading okay?

As was stated, it could be a bad socket where the pins aren't making good contact to the tube etc.

~Phil

[sluckey]

Don't measure filament voltage from chassis to socket pins. Maybe a pic...

[ViperDoc]

Thanks all for the info on this. Yes, I was checking each heater to chassis ground. NOOB! Just for clarity, the filaments all tested at 3.2 VAC WITHOUT TUBES IN. If the wire was broken somewhere, wouldn't one filament end test at 0 VAC?

[sluckey]

Just for clarity, the filaments all tested at 3.2 VAC WITHOUT TUBES IN.

Nice info to put in your original post. I still don't know how much voltage is between pins 9 and 4/5. You ever gonna check that?

[ViperDoc]

Just for clarity, the filaments all tested at 3.2 VAC WITHOUT TUBES IN.

Nice info to put in your original post. I still don't know how much voltage is between pins 9 and 4/5. You ever gonna check that?

Indeed, I just have to leave the office first! I will report.

[PaulD]

Don't measure filament voltage from chassis to socket pins. Maybe a pic...

Ok, see what you were referring to now, it was your reference to "filament wires" that confused me. To me that refers to the tungsten filament inside the valve, not the hook up wiring.