Valveking low volume

[rednax]

I put a master volume in my effects loop and a few days later the amp started popping and the sound was fizzy. I moved the tubes around and now there isn’t popping but the volume is really low(turning it up to five now is the equivalent of turning it up to one before). I’m pretty sure it’s a bad tube because one of the tubes is microphonic. But after I switched the tubes around it isn’t microphonic anymore. V1 is a jj ecc83 and V2 and V3 are Electro-Harmonix 12ax7 and don’t light up. Is there anything else I should check besides putting in an new tube?

[Jon Snell]

If none of the valves light up I would check the DC supply to them suspecting either R122 or one valve with heaters open circuit stopping current flow into the others.

[Enzo]

Jon, what schematic is that from? I don't recognize it.

[Delta362]

Looks like Jon's snippet is from the ValveKing II, attached. I've also attached a ValveKing schematic.

For the original ValveKing, the heaters for V3-V5 are in series, while V1 and V2 are parallel. Check sheet 10 of the ValveKing 112 schematic and see what DC voltages you have on the heater pins of all tubes. The heater voltage source is on sheet 8.

Which version of ValveKing do you have?

[Enzo]

On the original 50w VK, V1,2 are indeed in parallel, but then that pair is in parallel with V3 too. Then that triple threat is in series with the two power tube heaters.

[rednax]

I have the valveking 100 watt head, not valveking ii

[Enzo]

100 watt, OK here then.

[glebert]

Was the master volume external and just plugged into the jacks, or is it internal and installed at the effects loop position?. If is external I don't know what effect that could have on tubes. If it was internal and you had to remove tubes to install I would suggest maybe a cracked solder joint on a tube.

[rednax]

It was plugged into the effects loop, the preamp tubes are original so I might’ve killed them

[glebert]

I don't see any way that you could hurt the tubes by plugging in a master volume into the effects loop. The loop isn't even driven by the tubes, it is driven by a transistor. Since the master volume should only be able to reduce the signal to the next stage after the loop I don't see how that could be affected. I think there is more chance of damaging the effects loop jacks than the tubes.

[Enzo]

It is almost impossible to damage a preamp tube by connecting things to the amp.

[glebert]

I don't think there is anything you need to do other than trying a new tube, maybe get a spare as well. I would compare the volume level without the master volume to start with, to reduce the variables as much as possible.

[rednax]

I got a new preamp tube and moved the other tubes around and it did nothing. I plugged the fx loop send into the clean channel of another amp and it sounded fine. I just put new power tubes in 6 months ago so I don't think they are the problem.

[g1]

What does it sound like if you plug your guitar straight into the FX return? Still fizzy, or clean?

[rednax]

I noticed that the noise changed when I wiggled the v3 12ax7 so I desoldered the socket, sprayed it with contact cleaner and soldered it back in. Now it’s working. Thanks for the help