NAD - Mesa Boogie Rectoverb 50 - Series 2

[KraftyBob]

Well, new to me anyhow...

I have another post asking for opinions about the amp, but since I went ahead and bought it I figured I'd post the obligatory NAD thread The amp is like new and has the blue alligator skin Tolex - which initially I wasn't sure about but I really like it in person. It's different. The previous owner put in a WGS Retro 30 speaker which I really like. Didn't have a chance to hear the stock speaker but I have no complaints with the WGS.

I did a fair amount of reading before I bought it and posted on my other thread that opinions on Mesa's seem to be like Sushi - you either love them or can't stand them. There's not much middle ground. But So far I'm really liking what I'm hearing - and that's at lower volumes. I’m pleasantly surprised how good the cleans are because being limited on physical space since we moved, I’ve made myself a personal policy of one in / one out and wasn’t sure what I was going to unload. Now I’m thinking my Fender HR DeVille might be a good candidate since I can get good cleans from the Mesa. Although, rules can be broken...

The Rectoverb has a parallel effects loop (like other older Mesa's) but there’s an easy (and reversible) mod to convert it to serial so I can use my Helix in 4CM like I do with my other amps. Anyhow, here it is:

 

[Matthews Guitars]

What's not to like? Mesas are great amps, and I've owned three Rectifiers, two Triple Recto Solos and one Dual Recto solo heads, which admittedly are not the best Mesa for me but they're still great at what they do. The Rectoverb is the same concept plus reverb, so I'd like that even better.

There's a Mesa for any taste, or so I believe. And Mesa is the only big name company that only makes amps to the construction standards of road worthy, giggable amps for the professional musician. They don't have a student line, or a budget series, or an entry level series.

I do hear one criticism often enough to make note of it, and that's technicians who say Mesas are hard to repair. Let me rephrase that with greater accuracy. Many technicians who are lacking in the skillsets that come of working on modern consumer electronics are lacking in the skills required to work on PC board based Mesa amps which are more complex than the simple "classic/vintage" amps they're used to.

Those of use who are experienced in modern consumer (and industrial) electronics and aren't afraid of PC boards or even (Gasp!) some circuits with surface mounted components in them, have little problem handling a cranky Mesa amp, not that this is even all that much of an issue as they tend to be quite reliable in general.

 

[KraftyBob]

I’ve been reading up on how the tone controls work and I think that might be a lot of the problem why some people don’t like them. They don’t function like typical T/M/B. The manual has a great explanation. For example, in the clean channel when the gain is cranked, the Treble and Mid can also add gain. And then it recommends keeping the bass below 10:30 to avoid flabbiness. If you’re not aware of those nuances I can see how someone wouldn’t like the sound.

One could ask why not just have them function normally, but there are some great tones to be had with how this works.

 

[Deftone]

I have a Single Rec. Solo head, series two. It rips. Super versatile. Just recently swapped out the V30's in my Halfback cab for 75w Creambacks and it got even better.



Not a fan of the parallel loop though. Plan on modding that.

 

[Ttepper]

One of my favorite amps! Never see them pop up in that condition any more. Great find.

 

[KraftyBob]

One of my favorite amps! Never see them pop up in that condition any more. Great find.

Yeah, not bad for a 20 year old amp. Snagged it for $700, which I think was a good price based on what others are selling for.

I’m really loving it so far. Bit of a challenge dialing it in as the tone controls work like no other amp I’ve played. But I like experimenting so it’s all good. Just have to remember that Mesa’s (rectifiers anyhow) are darker and looser than Marshall’s Once I do the mod to change the loop from parallel to serial I’ll get my Helix connected and put an SD1 or Tube Screamer in front to tighten it a little.

 

[texans1]

Longtime forum viewer but rarely post here. I'm a Marshall guy, but picked up this Mesa at Guitar Center around 2005. Used but in mint condition. A friend of a friend sold me the extension cab soon after. A great sounding and versatile amp. One of the selling points for me was the ability to change power tubes at the flip of a switch. I put in RFT/National EL34 power tubes and it sounds so good. Have not changed any preamp tubes. Both the amp and cabinet have the factory Black Widow speakers which I think sound fine. Congrats on your new purchase, and I like the blue alligator skin tolex.

 

[Frank Araneo]

It's the amp I MOST regret selling! Very versatile amp with lots of tonal options. Relatively portable too, for a Mesa combo. Having owned (and own) various Mesa Mark amps, I felt the Rectoverb could supply both the Mark articulation and the Marshall-esque grind. Fantastic amp for both rhythm and lead sounds, though I preferred it for rhythm. It took pedals well too. As with many earlier Mesa amps, 1) treble and mids do act as gain boosts, I believe above 5, and 2) best to keep the bass setting low, like 3 or 4, especially when boosting volume as they do tend to get flubby (like Mark series amps). IIRC, it has a switch that allows either 6L6 or EL34, but only diode rectifier, hence "single rectifier". IIRC, they came stock with a Celestion C90, standard on most earlier Mesa amps. Very capable speaker. I have a WGS Retro 30 in a Fender Supersonic 22, and I love it. I suspect it's a great match for the Rectoverb. Congrats on the beautiful amp at a really good price!

 

[KraftyBob]

I’ve been struggling to get a satisfactory tone from this amp when turned up. It also had very little clean headroom. As soon as I turned it up a little the clean channel would start breaking up. I figured I re-tube it since I didn’t know how old the tubes were.

Yesterday I opened it up to do the parallel to series effects loop mod and discovered that one of the screen resistors was hanging from the board on one end. I measured across the pads and sure enough it was open. It was also starting to melt the casing on the wire below (which I confirmed did not expose wire). Both resistors measured good so I removed them and soldered them to the top of the board.

I checked all the tubes in my tube tester and they all passed. Filter caps look physically good and they are well within spec on my ESR meter. Put everything back together and holy cow! Now there’s tons of clean headroom and the Modern channel sounds like what I was expecting a Mesa to sound like. It's like a new amp

You can see the lower resistor slightly underneath the upper one and the wire casing a little melted.



Fixed.

 

[Matthews Guitars]

What did you do? Take those resistors out and put them on the top of the board?
Congratulations, you just disabled a safety feature.

They were installed that way specifically so that in the event of a severe tube short, the resistor would get
hot enough to desolder itself and drop out, preventing further damage.

That was a very specific design choice made for safety reasons.

It's like a fusible resistor only without having to worry about finding a matching replacement.

I strongly recommend you put it back the way it was.

 

[KraftyBob]

What did you do? Take those resistors out and put them on the top of the board?
Congratulations, you just disabled a safety feature.

They were installed that way specifically so that in the event of a severe tube short, the resistor would get
hot enough to desolder itself and drop out, preventing further damage.

That was a very specific design choice made for safety reasons.

It's like a fusible resistor only without having to worry about finding a matching replacement.

I strongly recommend you put it back the way it was.

I didn’t realize that’s why they were soldered upside down. Usually the resistor will blow open, no? My first thought was why not rely on the HT fuse instead of solder to melt, but checking the schematic I see it doesn’t have an HT fuse (or a heater fuse either).

So apparently there was a tube failure in the past that caused this one to drop. Makes sense but you would think they would run the wires underneath differently instead of directly below since it was starting to melt it. I have to open it up again as I have a few scratchy pots to clean so I’ll change it back.

I’m assuming the amount of solder should be minimal so it can unsolder itself? Thanks for the information @Matthews Guitars

 

[Matthews Guitars]

Use just enough solder, but don't be too stingy about it. It needs enough for a secure connection. And don't crimp the leads over. The resistors should drop out when the solder is molten.

Yes I'd move the wires a bit. They should not be at risk of being in contact with a hot resistor.

Mesa sometimes uses some very "interesting" engineering solutions to common problems. This is one of them.

There is always a reason why Mesa does anything. If a part is on the "wrong" side of the board, when there's no reason it can't be installed on the opposite side, there is a reason why they did that.

When I first saw that in a different Mesa I was a bit puzzled until I realized what was going on. I had to stop and think about it, because I like to solve puzzles. "Why would they put that part on the back side of the board? And why is there no board under (or over) the resistor? Then I saw it...those resistors can run hot enough to scorch the board and render it conductive. So cut out the board under
them, solve that problem. And that hot resistor, if it gets hot enough, will unsolder itself and drop out. Actually brilliant!

 

[KraftyBob]

Use just enough solder, but don't be too stingy about it. It needs enough for a secure connection. And don't crimp the leads over. The resistors should drop out when the solder is molten.

Yes I'd move the wires a bit. They should not be at risk of being in contact with a hot resistor.

Mesa sometimes uses some very "interesting" engineering solutions to common problems. This is one of them.

There is always a reason why Mesa does anything. If a part is on the "wrong" side of the board, when there's no reason it can't be installed on the opposite side, there is a reason why they did that.

When I first saw that in a different Mesa I was a bit puzzled until I realized what was going on. I had to stop and think about it, because I like to solve puzzles. "Why would they put that part on the back side of the board? And why is there no board under (or over) the resistor? Then I saw it...those resistors can run hot enough to scorch the board and render it conductive. So cut out the board under
them, solve that problem. And that hot resistor, if it gets hot enough, will unsolder itself and drop out. Actually brilliant!

I relocated the screen resistors back underneath the board. I also loosely pulled back and cable tied the wires underneath so they weren't directly under the resistors.

I cleaned all the pots and jacks and took all the voltage measurements for a baseline should I need to reference them in then future. The bias voltage is -52vdc at the grid whereas the schematic indicates -48vdc - so it's pretty close. Interestingly the tubes (JJ's, not Mesa's) are biased at 20.5ma & 21.5ma. Which is pretty cold for 6l6GC's, but the amp sounds good.

 

[Frank Araneo]

Glad you are sorting it out! The majority of Mesa amps are biased very cold, like <50% max plate dissipation. Unlike Marshalls, they rely primarily on pre-amp distortion with a clean power section. Eurotubes (JJs seller) is very good at matching tubes to particular amps. I tell them the idle current of the amp and how hot I want the tubes to run (in fixed-bias amps). It is possible to adjust the bias point on Mesa amps by replacing resistors in the bias circuit. I own a DC-3 that routinely red-plated whatever EL84s I installed (it ran at >100% max plate dissipation) until I swapped the bias resistors. Now it runs at abut 70%.

 

[KraftyBob]

Glad you are sorting it out! The majority of Mesa amps are biased very cold, like <50% max plate dissipation. Unlike Marshalls, they rely primarily on pre-amp distortion with a clean power section. Eurotubes (JJs seller) is very good at matching tubes to particular amps. I tell them the idle current of the amp and how hot I want the tubes to run (in fixed-bias amps). It is possible to adjust the bias point on Mesa amps by replacing resistors in the bias circuit. I own a DC-3 that routinely red-plated whatever EL84s I installed (it ran at >100% max plate dissipation) until I swapped the bias resistors. Now it runs at abut 70%.

After reading some more about Mesa’s it’s like you say - they tend to bias them on the cooler side. I had a few Peavey Valvekings that were like Mesa - fixed bias amp but no trim pots to adjust. I ended up taking out the bias resistor and replacing it with a lower value and a trim pot so I could adjust the bias. Thought doing the same with my Revtoverb, but I think it sounds really good as is so I’m not sure I’ll change it.