Tube Guitar Amplifier problem--PLEASE HELP

[Smithha85]

I have a Tone King Falcon amplifier. I am having a very weird problem with it. The amp uses 3 12ax7 tubes, and 2 6v6 tubes. When I plug the amp into the wall and just plug a guitar straight in, it works great. However, when I plug my guitar into my pedal board and the pedal board into the amp, the amp dies temporarily. The amp does not take ANY input signal at all when this happens. Even if I turn it all the way up and touch the input cable, no buzz comes out or anything. HOWEVER, if I touch the cable to any of my pedals, I get sound--just a buzz, but a sound, nonetheless. I have replaced the tubes and tried different speakers, and all different cables, but the problem persists. Oddly enough, if I leave the amp alone on standby, it starts working again after 25 minutes or so. When it "comes to life," it works great, but as soon as I touch that input cable to my pedals again, it dies. When it "dies," the tubes all light up still, and the amp appears to be functioning fine, but it will not amplify ANY input signal at all except for the buzz I get if I touch the cable to my pedals

I have 5 seperate pedals on my board, and each is powered by a single adapter that branches into 5 different outputs for the pedals. There is one pedal that takes a different adapter, so that is powered with a different adapter. both of those adapters are fed by an extensinon cord that is connected to a Furman Power conditioner, which is plugged directly into the wall. The amp is also plugged straight into the Furman.

WHAT IS GOING ON HERE???? Please help.

 

[Mr RB]

It's probably something to do with the pedal power adapters. Pedals generally expect the jack plug outer ring is earthed. If their power adapters raise their level away from earth you can have problems, likewise if your amp does not like earthed jack plugs.

Do you have a schematic for the amp?

You can try tests of each pedal with only that pedal attached to the amp. With or without the pedal power supply lugged into the mains.

 

[Smithha85]

Okay, I will try to isolate each pedal and see if the problem replicates itself on one or all of them. I use an iSpot power adapter to power all of the pedals. It only has two prongs, though. I don't have a schematic for the amp, but I can try and dig one up. In case you didn't realize this, I am not very savvy with this kind of stuff! Thanks for your reply. Finally, suppose I find the problem in a pedal or a power adapter, how do you explain the amp's response to the problem? That is, why would it stop working--remain "on" tubes glowing, etc, but just no sound--and then suddenly start working again? It's not that a "cool-down" thing, either, because last time it did this, I unplugged it for a day before I plugged it back in, and it still didn't work. Only after idling for 20 or 30 minutes did it "power up" again. The symptom reminds me of something that just remaganatizes or recharges or something. . . . Also, I have used the same pedal setup on all of my other amps, and I've never had a problem. How could that be explained? This is weird and confusing, indeed. . . . Thanks again!

 

[Mr RB]

I'm not really sure about the amp cool down symptom, that sounds quite unusual and I would only be taking a wild guess.

But it is common to get issues from mains powered pedals and tube amps. In some cases people will even run a small audio transformer (small balanced transformer) between the pedals and the amp input. That fixes any issues caused by different voltages between the amp and the pedal setup.

 

[alec_t]

I'm not familiar with either the amp or pedals but that delayed start-up smacks of a capacitor charging or discharging through a very high resistance. Perhaps a bad solder joint or a leaky cap?

 

[unclejed613]

check for any DC offset on the output of the effects pedals. if the tube amp isolates the input using an electrolytic cap, leakage currents through the cap (can happen when the + side of the cap is toward the input, and the - side toward the tube's grid, and the offset on the input is negative) can send the tube's grid towards cutoff, greatly reducing the gain. when you remove the input, the cap may retain a negative charge on it until the charge bleeds off through the leakage resistance of the cap.