Ampeg V2 No Filiment Light

[plexi50]

I recapped this V2 yesterday and everything looks good except for 3 tubes that show no filiment light in the tubes

All the tube sockets read as shown in the pic. I can put the tubes in and still read the voltages as shown in the pic but still no filiment light

Pins measured across each tube 4&5 / 4-5&9 / 1&12 i read 6.32 VAC

All these tubes test good in my tester and light up in the tester / What the heck is this problem? Current draw?

I removed the hum pot wires. Grounded pin 8 of the power tubes and used (2) 100 ohm resistors off pins 2&7 to ground

[PRR]

Put one meter probe in pin 4, one in pin 9. (Not to ground.)

Is that 6V? Or zero?

What are plate voltages? Full 400V or normal 200V?

You WILL want the hum-pot with the PCB heater wiring; CENTER-tap works OK when heater leads are well-balanced, but they can't be symmetric on PCB; you need to be able to trim 47% off-center to match the PCB trace asymmetry. Or better yet, Dremel-off the heater traces and wire with twisted leads like it should have been.

[eleventeen]

Almost has to be a bad trace or bad socket somewhere, no?

My reco: Remove ALL of the subject tubes. Leave the others in. Figure out a semi-durable way to make a decent contact with one of the heater pins on one of the intermittent tubes. Could be a fat resistor lead stuck in the socket, if a 9-pin tube, or, a vector-style test socket. Or maybe you can make & then clip to a teeny solder connect on the exposed portion of the socket terminal.

(I am trying to use the term "heater" instead of "filament" based on PRR's post on that topic a few days ago)

Do the same to the other side of that same tube's heater. You are relying upon the near-short that should exist consisting of the transformer heater winding & the remaining tube heaters. Then you just have to poke at things until that short goes away.

I think you probably have either a bad socket pin, or a "conditional connection" where a "Y" or a "T" or a branch in the foil trace has a hairline crack. It is also possible that the foil traces are jumpered up to the component side of the board to jump over some traces and then back to the foil side, and a bad solder connection exists just for that jumper.

[plexi50]

Put one meter probe in pin 4, one in pin 9. (Not to ground.)

Is that 6V? Or zero?

What are plate voltages? Full 400V or normal 200V?

You WILL want the hum-pot with the PCB heater wiring; CENTER-tap works OK when heater leads are well-balanced, but they can't be symmetric on PCB; you need to be able to trim 47% off-center to match the PCB trace asymmetry. Or better yet, Dremel-off the heater traces and wire with twisted leads like it should have been.

I have 0 VAC across pins 4 & 5 on the 6KII board. The main preamp board has 6.32 VAC across pins 4 & 9

Plates are 400 VDC

[eleventeen]

My money's on a bad trace, or bad interconnect wire between PCBs. I can see they are different boards due to the different color.

[plexi50]

I just checked the heater wires to the 6KII board and one of them pulled right out of the socket. Needs a cleaning and resolder. Back in a  bit with the test results /

[plexi50]

Ok i have 6.23 VDC across pins 4 & 9 now. Tube filiments are light up

This problem was solved by cleaning and resoldering the heater wire that pulled off the board

I resoldered all the tube socket pins as well. Man these old Ampegs really take a beating over the years

Most of the solid core wire itself is brittle and snaps in half from the excessive heat over the years

I figure 39 years is a long time if the amp has had constant use over the years / Thanks all!

[eleventeen]

Nice! Nobody can accuse you of givng us bad pix to work with. Carry on!