Rectoverb Issues ... Need Help

[Anfoguy]

Hello everyone.. I have a strange problem with my rectoverb solo 50 v2. The major problems are when I play the amp loudly
( i.e. channel 2 master at 9:00 and output at 11:00 or higher) the tone is so bad that the amp is useless. It becomes very flabby and weak, also the crunch of the distortion disappears, and also the volume cuts in and out quickly every so often. Note that I have the bass and gain turned down when volume is high. Another issue is the presence knob does nothing before 3:00 on raw and vintage modes but it seems this is a common occurrence among rectifier owners. When I pulled the chassis out to examine electrical components, I noticed a small cylinder (most likely a resistor) was not connected on one side so it was dangling, though there didn't appear to be any solder on it like on a similar one right next to it. So, I am not sure if it is supposed to be like this. It does not make sense to me to have a component that's not connected. Anyway I ordered new JJ 6l6's which will arrive soon so I can determine if the problem lies with the power tubes. I dont think the issue lies with tubes though since i have e34l's that perform the same way when the amp is turned up and they're newer than the 6l6's that are currently in the amp. Is it possible that the single c90 speaker in the combo can't handle the high volume? Another thing to keep in mind is that the reverb tank is not plugged in. I doubt this has a bearing on the amp's performance though. I would greatly appreciate any ideas or advice on how to fix the problem and where it the problem lies, that is the tubes, speaker, or circuitry. Thanks.

 

[Blaklynx]

-Check preamp tubes. You don't say how old or if you've changed them. V1 can be the culprit. They this first or just get a new set and have as spares.
-Gain turned down? How low? You should get decent sound even at 9oclock.
-Bass turned down? How low? (9oclock should be OK). I wouldn't turn it any lower. I've tried lowering tone controls very low and the amp just isn't 'alive' and the amp sounds 'bad' but I've not had the issues you have.
-Photo of internals. Can you post one? Someone may be able to tell you if this part should be connected (suspect it should otherwise why is it there?)
-Presence knob sounds suspicious. Not sure what part of circuit controls this > Could it be the part that isn't soldered?
-C90 speaker is fine.
-Reverb tank I'll tend to agree with you but I'm not 100% sure if it may play a part. Why not plug it in and have the reverb dial at zero? Also, the connectors for the tank > are they touching anything? Are they individually wrapped in tape to insulate them? You can't leave the end of signal cables hanging free uninsulated/not covered. It's like a guitar cable that doesn't have a guitar plugged in it but it's plugged into the amp.
-Electrical supply to the amp > is this OK? Playing an amp very loud can take a lot of power. I notice lamps sometimes 'flicker' when connected to the same line/power point and playing really loud especially low 'chugga-chugga' notes. Try different electrical points with amp only.

I'm not a tech. These could be some basic things to look at. Somehow, I suspect that your preamp tubes could be at fault here. Buy some for spares anyway. It's amazing how many tube amp owners don't have spare tubes!

 

[Anfoguy]

Hey thanks for the ideas.. ill makes some tests and post some pics. To answer some of your questions, the preamp tubes are about a year old at this point so I don't think its them but there is a slight hiss and crackle on high gain channels so it is possible some have gone bad. When playing loud the tone is so flubbed out and undefined unless i turn the gain down to a max of 10:00 and the bass pretty much the same. The reverb tank wires are not connected at the amp but are connected at the tank so they can not alter the signal chain unless the amp was designed to have it plugged in.
I'll plug the tank in, swap preamp tubes, and i'll get a pic of the internal up soon. Thanks for the help Blaklynx.

 

[94Tremoverb]

Where is the resistor that looks broken - in a slot in the board near the back of the amp? (Just wildly guessing, but...) If so, that's a screen resistor and it being broken would leave the amp running on one power tube only - which would explain the bad distortion, flubby tone, and (although you may not have noticed if you don't play clean) lack of a usable clean sound above very low volume, and the amp will also lack power. If so, that would also explain why changing the power tubes made no difference. Just a guess, but based on one of the more common reasons for a problem like this! The usual cause of a failed screen resistor is a blown power tube too, so it may not have been unnecessary to buy new ones.

By the way, although you're OK with this amp because the reverb is solid-state driven, in general it's a bad idea to unplug the reverb cables - in an amp with tube-driven reverb you could blow the reverb driver tube or the transformer. If you don't want reverb, turn the knob to zero .

 

[Anfoguy]

I'm gonna take a look at the internals again tonight. If i remember correctly it was near the back above a power tube. Also I swapped the preamp tubes and changed power tubes with no difference in sound.. also plugged the reverb back in. Something I noticed while swapping power tubes was that one was much hotter than the other.. indicating that a bad screen resistor could be the problem like you said. And finally I did forget to mention that my clean channel gets a little fuzzy at higher volume even with gain at 10:00. Thanks again for the help, looks like we're closing in on the issue here. I'll take a pic of the suspected blown screen resistor and post it tonight.

 

[Anfoguy]

Here are the pics.. The two black pieces are the things to look at. They are wired to the power tube circuitry. Notice how the bottom one is detached on the right side. This can't be good right?

 

[Blaklynx]

Here are the pics.. The two black pieces are the things to look at. They are wired to the power tube circuitry. Notice how the bottom one is detached on the right side. This can't be good right?

I'm no amp expert and don't know what I'm looking at but it does seem that it should be soldered on. A manufacturer isn't going to put a component on with only one side soldered. It also seem that tehis part's leg has broken off the solder pad (although I don't see any legs protruding through the solder pad. Maybe it was a dud joint to begin with. Does happen. I say solder it.

 

[Anfoguy]

Alright sounds good. Its amazing that this little resistor can cause so much mayhem in the amps operation. Hopefully this is the only thing causing the problem.. Thanks for the input again.

 

[94Tremoverb]

Yes, those are the screen resistors, and with one like that the amp is only running on one tube. (No special genius required to guess that before! Just a little theory and a lot of experience... )

It's the one that feeds the left-hand socket in your pics, and it's possible that the tube that was originally in this socket is dead - a shorting tube sometimes overheats the screen resistor enough to make it desolder itself.

 

[Anfoguy]

Ok nice.. thanks for the reply. So do you think the resistors are damaged by overheating and aren't within tolerance anymore? Or re-soldering should be enough to fix the problem?

 

[94Tremoverb]

Wirewound resistors (of which that is one) don't go out of spec - or not significantly enough to matter, anyway - they either survive or burn out. So if you resolder it and the amp now works properly, don't worry about it. If it doesn't, replace.

By the way, I would also remove both resistors and fit them from the *top* side of the board - it's a double-sided, through-plated board so it doesn't make any difference which side the component is on - because that way, if the resistor overheats enough to melt the solder, gravity will hold it in place not make it fall out, which may give you better survivability from a tube failure.

 

[Anfoguy]

Alright great info right there. Yea it would also be much easier to fix in the future if their top side since theyre kind of hiding under the board. I've never soldered anything before but do have an iron.. I might bring it to a good tech near by. I know its not very difficult but I'm a little hesitant to mess around near the amp's internals. Though I might not even need solder now that I think about it since there is probably enough still on the board and wire. Maybe I can just apply the iron and it will reattach.

 

[Blaklynx]

Alright great info right there. Yea it would also be much easier to fix in the future if their top side since theyre kind of hiding under the board. I've never soldered anything before but do have an iron.. I might bring it to a good tech near by. I know its not very difficult but I'm a little hesitant to mess around near the amp's internals. Though I might not even need solder now that I think about it since there is probably enough still on the board and wire. Maybe I can just apply the iron and it will reattach.

Be careful. There's irons and there's irons. There's 20/25W, 40W and yet others are higher. If it's too hot, you may damage something. A 20/25W should be enough. Do you know what iron you have? I'd be very cautious with a 40W, they are pretty hot.

And you may need some new solder as the old solder may stay on the tip of the iron when you melt it and won't be enough to run back onto the leg and solder pad. You want a good joint, not a weak joint and/or a dry joint.

Take it to a good friend (if you can) that knows how to solder if you're unsure. It's not a hard job as you can see. Or simply go buy a low wattage iron (if you don't have one) and some solder (yours to keep...LOL) and do it your self. I'd hate to think a tech will charge you for one solder joint. It'll take him 1 minute to do, talk with you 10 minutes and charge you 15 minutes or half an hour, unless of course he checks your amp to make sure it is running well and the amp works as it should..... then that's different.

 

[guitardr]

You should really contact Mesa.
If it's less than 5 years old and you did not mod it in any way, it should be covered.
Also: see if there's a warranty center or knowledgeable tech nearby to pose this question to. I have a demo/"new" Rect-O-Verb Series II 50 head that I want to change it's FX loop (parallel to series) and I sent a message to a sharp forum member.

 

[estring]

I had screen resistor fail about 3 months ago. cost me $70 to fix. Take it to a shop!!!!

 

[TREZZ HOMBRES]

Just replaced my reverb tank that I got from MESA Parts, Tech support was a lot of help in diagnosing the problem with my REVERB.

(process)
I changed Tubes around with no luck. I also checked ohms on the tank itself with really no definitive diagnosis. When I took the old one out of the amp box, I could hear faint spring sounds when I touched them with the amp turned on. This was a good way to check the pot's on the Reverb Channel and the foot switch as well. To be clear this was a 50W Rectoverb head. I use this amp a lot and play live it sounds amazing!! My band uses MESA exclusively
as we need that tone.

Thanks to Mesa tech support you have never let me down