Engl amp -strange problem!

[Valvehead]

I have an Engl Powerball head here thats got a weird problem . It comes "on" randomly when in standby mode.

This amp has the 2 rocker switches similar to a Marshall , power and standby .

I unhooked the 4 wires off of the standby switch and it still does it ! So its not the switch .
Its got to be shorting somewhere on the board ?

[Enzo]

Follow the switch wires back to wherever they came from and see what's touching what. Or look for signs of arcing.

Turn all the room lights off while the amp is powered up but in standby, then watch the circuit board. If ti arcs, you might see a small blue spark.

[Valvehead]

i will try that , heres a similar Engl scem , looks like theres all kinds of stuff going on with the standby

http://www.freeinfosociety.com/elect...l_Fireball.pdf

[Enzo]

If that is like your model I don't see that as a lot of stuff, it is simply opening the cathode lead from the output tubes. B+ is in the circuit all the time. A leaky tube could cause something like this. Have you tried different power tubes? They don;t have to be new tubes, just tubes that we know work. If it stops doing it while wearing different tubes, then we know it was a tube. Possible heater to cathode short.

[Valvehead]

have you seen another amp that uses this standby method ? I thought it was out of the norm.

It could be a tube, they are about 2 years old , however , i cant get the amp to act up right now. Maybe i will talk the owner into a fresh set.

[Enzo]

Yes, this is nothing new.

[izzybell2810]

I repaired a Powerball last week, not the same prob as yours, (Bad plate resistor on Pre/A tube 2 causing a lack of vol on ch2) but giving the boards a check over I found several suspect solder joins mostly around the power tubes.
Just thought I'd add that!

[Tubis]

I have a powerball in my shop with this problem. The customer claims that it from time to time came alive in standby. When he changed the tubes it persisted but intesified right before one of the tubes shorted out. I tested it for two ours with a new tube.... and nothing. Then I tested it with the old tubes and...nothing. Sence i cant see the fault for my self Im realy pulling my hairs. I cant se anything on the schematics besides a tube fault that would cause this. But....when i asked Engl they claimed that the ZY150 zener on the cathode could be faulty. I dont get that. How could that possibly make the tube draw current so that the amp comes alive?

[g1]

Have to agree with you, even if the zener goes dead short, it can't connect the cathode to ground. The only way I can see is if the zener was mounted to the chassis and somehow shorts to it.

[Tubis]

I dont rely get Engls tech?

"anode - kathode line is connected by the relay switch contact, not by the ZY150 diode.
Please check the relay contacts, too"

Say what? There still isnt a path for the current. (takes weeks for him to answer so i kind of gave up there)

Question to the forum. Is it possible that there could be an arc to the relay coil? That would take the current to ground point. Does that happen in relays? Or could there be an arc between the inputs in the "sense" relay, that would also make a path for the current.

[Enzo]

How about the standby switch itself? If the switch is broken inside or is arcing, you get operation of the amp.

[Tubis]

How about the standby switch itself? If the switch is broken inside or is arcing, you get operation of the amp.

Off course. But it seems really stable when flipping it. And there is very low voltage over it in this position so it would take a really broken one to make the current jump here and make the amp playable.

[Enzo]

The mechanical latching part may feel fine, but that doesn't tell you that there is not a flake off a contact floating inside.

Really broken? Again, not really. I am not assuming there are voltages high enough to arc the switch, I am thinking we have some mechanical intermittancy. A loose flake of metal inside that sometimes falls against the switch contacts. But anything is possible.

Never think up reasons not to check something.,