Dual Recto Problem!

[davemintynz]

Hey guys

Got a couple of problems and thought id see if I could get some help from here first before spending a fortune getting a tech to fix something that may be simple to fix.

Ive got a Dual Rectifier Solo running into a Orange 4x12 Cab which i bought second hand. The last owner had it serviced where the tech fitted a Fender/Sovtek power tube but left the other MESA tubes in there, which is a bit of a concern to me as they obviously not matched. Also this was a USA import amp so im having to run a 240V Power Transformer to convert the New Zealand 240V Mains power to suitable voltage. Also noticed when switching the standby off there is a large spark in the Sovtek power tube.

First Problem only happens bout once every month. Ill be playing away at high volume when all of a sudden the volume will drop off and it will go all "crackly" sounding and it will go away and be fine if i turn it onto stand by and wait 5 minutes.

Second Problem - When i switch the rectifier switch from TUBE RECTIFICATION to SOLID STATE RECTIFICATION the two power tubes furthest to the left (one of them being the Sovtek tube) rapidly get really hot and glow bright orange! which in-turn causes the fuse/breaker on the Power Transformer to blow.

Is it possible that the un-matched / Sovtek tube are causing the problem?

Hopefully someone out there can help me PLEASE!

 

[twothemax]

Hey guys

Got a couple of problems and thought id see if I could get some help from here first before spending a fortune getting a tech to fix something that may be simple to fix.

Ive got a Dual Rectifier Solo running into a Orange 4x12 Cab which i bought second hand. The last owner had it serviced where the tech fitted a Fender/Sovtek power tube but left the other MESA tubes in there, which is a bit of a concern to me as they obviously not matched. Also this was a USA import amp so im having to run a 240V Power Transformer to convert the New Zealand 240V Mains power to suitable voltage. Also noticed when switching the standby off there is a large spark in the Sovtek power tube.

First Problem only happens bout once every month. Ill be playing away at high volume when all of a sudden the volume will drop off and it will go all "crackly" sounding and it will go away and be fine if i turn it onto stand by and wait 5 minutes.

Second Problem - When i switch the rectifier switch from TUBE RECTIFICATION to SOLID STATE RECTIFICATION the two power tubes furthest to the left (one of them being the Sovtek tube) rapidly get really hot and glow bright orange! which in-turn causes the fuse/breaker on the Power Transformer to blow.

Is it possible that the un-matched / Sovtek tube are causing the problem?

Hopefully someone out there can help me PLEASE!

hi. the 2 tubes on the far left are rectifier tubes and not power tubes. the other 4 are your power tubes. and the small ones with the tube shield are your preamp tubes. the 2 rectifier tubes will only become fully functional when you have your switch on tube rectifier, otherwise they just sit idle. i think you can remove those two tubes and switch your amp to solid state rectifier to check if thats your problem. i think your in line for a retube. usually a crackly sound means tubes are going bad. probably one of your 4 power tubes, best to put in a match quad set and a set of preamp tubes as well.
did you just buy this amp. was it shipped with the tubes installed or taken out. if the tubes were taken out and you reinstalled them what can happen is burnt material on the tube can become dislodged during shipping and when reinstalled and your amp turned on the heat burns this material and makes a crackly sound and you will loose vol and power. this happened to mine. i chaned ny tubes and never had any problems.
hope this helps

 

[94Tremoverb]

Throw out the Sovtek tube NOW. Any tube that arcs under any conditions is faulty and a risk to the amp. It's also shorting the bias out when run at the higher plate voltages from the solid-state rectifier, which is why it makes the other one on that side of the amp run hot as well. This is also probably the cause of the crackling and drop in power.

Using a single tube that may not be matched to the other three is not inherently bad in itself - it may even be matched, you can't tell from just the brand - but this tube is just bad. I will also often change just one tube if only one has blown, and I will usually use another spare used tube as well, but I do check that the replacement is reasonably well matched to the others and that it isn't faulty.

Personally for your amp, I would now change all four power tubes and keep at least the two definitely good Mesa tubes as spares. The other tube that runs hot may not have been seriously damaged, but if you really want to be safe I would mark that one as at least questionable as well and may not bother to keep it. (I would probably only use it for troubleshooting.)

I wouldn't change the preamp tubes yet, since all the problems are almost certainly caused by the faulty power tube. If you've got a new set of power tubes in and it's still doing it, check the rectifier tubes next, and the preamp tubes only after that.

 

[mikey383]

hi. the 2 tubes on the far left are rectifier tubes and not power tubes.

It depends on your perspective. Looking at the back of the amp, the 2 on the right are the rectifiers.

I agree with '94. Toss that Sovtek and the one next to it. Replace all 4 just to be safe.

 

[davemintynz]

Yeah i meant the ones on the left if looking from the back. Sorry should have made that a bit clearer. I will replace the power tubes and see how i go. Im pretty confident that the sovtek tube is the problem.

Ive had the amp for nearly a year. And most of the time it works fine.

Cheers for your help guys. Much appreciated