Mig 50 sparking tubes. Help.

[Gr8Scott]

I know the first answer is to take this amp to a tech. That is definitely in the plan book as soon as one can be located (my old tech moved and started Mojo). For now my nephew knows not to run the amp until it's been serviced. The amp is fine on standby, but one of the tubes starts sparking when taken off standby. No input sound makes it through and it makes nothing but crackling noises. Seems like seriously bad juju to me. What other than bad tubes is likely to be wrong with the amp? We're getting sound and we're getting power. Sounds like the transformers aren't likely to be the problem. I'm leaning towards bad tubes or capacitor or resistor failure/drift.

 

[idsnowdog]

Re: Mig 50 sparking tubes. Help.

I don't think the amp would be all that difficult for a tech to troubleshoot since it is pretty much a bassman circuit.

 

[Lewguitar]

Re: Mig 50 sparking tubes. Help.

It's probably just a bad tube...but you'll have to replace both. If you have a pair of used ones you could stick 'em in and just see. I wouldn't put new ones in right away because if the problem is the amp you might ruin your new tubes. But try a set of weak oldies if you have a set and see what happens. You'll need to have the bias reset if you do replace the power tubes.

Don't turn the amp on again with that bad tube in there...you could fry the resistors on the tube socket or worse.


Lew

 

[Gr8Scott]

Re: Mig 50 sparking tubes. Help.

It's probably just a bad tube...but you'll have to replace both. If you have a pair of used ones you could stick 'em in and just see. I wouldn't put new ones in right away because if the problem is the amp you might ruin your new tubes. But try a set of weak oldies if you have a set and see what happens. You'll need to have the bias reset if you do replace the power tubes.

Don't turn the amp on again with that bad tube in there...you could fry the resistors on the tube socket or worse.


Lew

I've assigned my nephew to finding an older set of tubes that he had that were still good when he replaced them. He had TAD short bottle 6l6's in there and one of those were sparkling like the 4th of July. I figure that the tubes are bad no matter what also. I just wonder if there are other possibilities as well. Mig 50's run at very high voltages, but if they didn't I'd try throwing in a set of 6V6 tubes. Unfortunately that's not gonna work. He has a set of KT-77 tubes, but they are more like EL-34 tubes in terms of pinouts and I don't want to mod the amp just to find out that it's something else that's wrong.

If he can't find his old tubes, I'll get him a new set from Mojo. They have good prices.

 

[kevlar3000]

Re: Mig 50 sparking tubes. Help.

Hopefully just a tube, but you might have cooked a resistor or two. I blew the screen grids on my Stramp with a bad tube, easy fix, but was stressed when it happened!!

 

[Gearjoneser]

Re: Mig 50 sparking tubes. Help.

Look inside the chassis, and closely inspect the power tube sockets to see if there's a resistor burned or if something is arcing across 2 of the socket's terminals.

One time I had an amp that was like 4th of July, and tracked it down to one of the wires coming off a tube socket. It was dangling 1mm from the chassis.

 

[Gr8Scott]

Re: Mig 50 sparking tubes. Help.

Tubes were the problem. Nephew found his original tubes (which were still in good shape) and put them in and the amp is working perfectly and sounding great. I'm quite happy that it was just the tubes. Those mig 50's run really high voltages (roughly 590 volts) and it just wears the tubes out IMHO.

 

[JB_From_Hell]

Re: Mig 50 sparking tubes. Help.

Glad that it wasn't a big problem.