Maverick Mod: Rhythm channel Blackfaced (Lone Star-ed?)

[steeve]

I'd been JONES-ing for a Maverick for about 12 years and finally got around to getting one in September (it was a short head). The Lead channel has that poor man's Dumble vibe to it but the Rhythm channel is kinda boring, lacking the sparkle of a Fender blackface amp. When you look at the schematic it is easy to understand where the sparkle went: between the input jack and the grid of the initial preamp tube there is a 1M5 series resistor (instead of the 68k low/34k high values in the BF design) and that resistor is bypassed with an 180pf cap to cut the bass. The normal 1M grid load is there but it is bypassed with a 500pf cap to cut the highs. Small wonder that you don't get the rich tone of a blackface amp.

The Maverick Rhythm channel preamp is almost identical to the Subway Blues, with the addition of the Fat/Bright switch. When you look at the Subway Rocket you can see where Mesa came up with the 1M5/180pf RC network on the input; on the Subway Rocket it is used to isolate the signals being sent and returning from the extra gain stage used for the Lead channel. Same concept as the 3M3/10pf reverb splitter that Fender used on the BF Reverb amps. So I guess that Mesa wanted the Subway Blues to sound like the Clean channel of the Subway Rocket for one reason or another so they left that 1M5/180pf RC network on the input. And I guess they wanted the Rhythm channel of the Maverick to sound like both of those.

Rewiring the input to BF specs is very simple but it would increase the overall gain of the Rhythm channel. So why not just Blackface the whole Rhythm channel preamp? Well for starters, there is an extra gain stage in the Maverick that the BF preamps don't have so that must be dealt with- this is getting too complicated for me! :? And then it occurred to me: wire the 3rd stage exactly like the reverb recovery stage on the BF amps. So I inserted the 3M3/10pf reverb splitter between the 2nd gain stage and the 3rd even though the actual BF reverb circuit was not there. (I actually used a 2M2/15pf splitter as a compromise between Boogie and Fender.)

The Rhythm channel sounds great now, similar to the Rhythm channel on the Lone Star but with the added Fat/Bright switch. Plus it has its own dedicated tubes (V1 and V4) and doesn't have to share them with the Lead channel so you can voice each channel with different tubes.

There was one change I wanted to make to the Maverick Lead channel- the 1M grid load to the initial gain stage is bypassed with a .001uF cap. It was a simple matter to remove that cap and the Lead channel is much more touch responsive and gets a nice clean sound when you back off the volume control on your guitar. (IMO the stock Mav Lead channel just got kinda wimpy and blah when you backed off the guitar volume control.) I think it goes without saying that the Maverick Lead channel beats out the Lead channel on the Lone Star so I think I now have the best of both designs.

I will be drawing up all of the mods I did and will share them with whoever wants them.

Disclaimer: Opinions expressed are my own. I tried some tube rolling with the stock Maverick to improve the sound from what it was like when I bought it. V1-V4 = GT5751M/GT5751M/GT12AX7M/GT12AX7M (for stock and with mods.) With the mods it sounds good with GT12AX7M's for V1 and V4. Or some NOS 12AX7's if you have them.

Steve Ahola

P.S. One problem I had with the short head was that the reverb tank stuck out of the bottom of the cabinet. Some of my cabs have handles on the top and that would keep the reverb tank from floating freely. So I took one of the feet and the screw down to the local hardware store and found plumbing washers (for sprinkler valves) which had the same outside diameter as the feet. I got 12 of the washers along with 4 screws about 3/4" longer than the original screws. Although I haven't done this yet it would probably be a good idea to epoxy the 3 washers together that go under each foot.

 

[plucker]

Hi steeve interesting reading I would be interested in seeing what you have drawn up to maybe try some on my Maverick.

I'm still having a problem ith the lead channel on mine when I first switch on from cold after about a Minute Relay 3 (channel switching) Starts chattering like crazy it lasts for about another minute slows down and stops then seems to work fine.

Any ideas anyone please.

Thanks

 

[steeve]

Hi steeve interesting reading I would be interested in seeing what you have drawn up to maybe try some on my Maverick.

The preamp circuit itself is almost identical to the Lone Star and the AB763 Super Reverb circuit. What took figuring out was where all of the parts are located on the PCB. If you choose to do it I think that you want to incorporate the whole circuit, although I'm sure that someone could get better results fine-tuning the component values.

I'm still having a problem with the lead channel on mine when I first switch on from cold after about a Minute Relay 3 (channel switching) Starts chattering like crazy it lasts for about another minute slows down and stops then seems to work fine.

I know absolutely nothing about the relay switching circuitry in the Maverick but it sounds like a sticky relay to me. Can you get a replacement relay from Mesa or can they give you the specs so that you can find one at Mouser (or wherever)? I've never soldered a relay on a board because I was afraid I'd damage it with the heat, but on the other hand if you use a socket you need to deal with the possibility of the relay vibrating loose and falling out. (Drilling holes in the pcb for a cable tie will sometimes take care of that.)

Then again if it works fine after waiting a minute or two you might want to leave well enough alone. One trick you might want to try is to activate the relay on and off maybe once every 30 seconds for 5 minutes. (Don't do it too fast or the coil might overheat- just a guess but I'd rather be safe than sorry!)

Good luck!

Steve Ahola

 

[plucker]

I replaced the relay i got a couple of mesa but it made no difference all voltages are more or less ok according to the schematic its had new dmr and filter caps just annoying when it happens thanks anyway.

 

[steeve]

I replaced the relay i got a couple of mesa but it made no difference all voltages are more or less ok according to the schematic its had new dmr and filter caps just annoying when it happens thanks anyway.

If it is okay after a minute or two I could live with that. Or does it screw up like that after the amp has warmed up?

If other people are having problems with Relay 3 I wonder if it might have to do with its location- with perhaps heat from the tubes or EMR from the transformers affecting that particular spot. Or it could be gremlins- I heard that they have problems with gremlins in Petaluma.

Steve

 

[steeve]

I've been pleased as punch with the rewired Rhythm/Clean channel on my Maverick- so much so that now the Lead channel is starting to sound like a one-trick pony, er, maverick. :mrgreen: I kept looking at the schematic hoping for inspiration, but was coming up with absolutely nothing since it is so unusual. And then it occurred to me... "3 gain stages- I could rewire the preamp as a Soldano SLO!" :lol: (In 2008 I had rewired several Crate V18's as different classic amps and the SLO conversion turned out really nice and very popular among the modders over at TGP. One thing I particularly liked about the SLO conversion was how well you could go from clean to overdrive just by adjusting the volume control on your guitar.)

I was thinking that it would be a real hassle to bypass the fixed tone stack after the first gain stage but removing two resistors will take it out of the circuit completely. (Very easy to do AND very easy to undo if I don't like the results.)

I will be creating layout drawings showing the location of all of the components in the tube audio path of the Maverick, so if anyone wants to have it fine-tuned they will have a road map, so to speak. And I will create layout and schematic drawings of the modifications I have done to my own Maverick.

Steve Ahola

P.S. I think that the Mavericks will come down in price even more since it has almost been 10 years since Mesa took them out of production. They are a real workhorse (sorry! ) and with some fine-tuning (or more complicated rewiring) you could get quite a few different sounds out of them.

 

[Monsta-Tone]

Hey Steeve,
Welcome to the forum! I've been reading your thoughts and drawings for a long time!
I would be really interested in the mods. I actually really liked the Maverick cleans, but hated them with the stock tubes and output transformer.


Plucker,
As for the relay chatter, there are a couple of things you can try......
There are several components that make Relay 3 work. There is a 4N33 chip and a 16426 transistor that create the path for the voltage to flow for the relay.
I have seen lots of the chips and transistors go bad over the years, but mostly in the older .50 Calibers and Mark III's. I have seen them go bad in some early DC's, which the Maverick got most of it's circuitry from.

You can get the transistor and the chip from Mesa for under $10.
While you are in there, and just to make sure this is fixed, you should check all solder connections on the bottom of the board for the relay.
Also check all solder connections on the board in the switching matrix.
And.....finally, you might want to think about replacing the 10uf 25v capacitor that is in parallel with the coil of the relay. It could be that the voltages are correct, but are not rising fast enough or are not steady enough to keep the relay closed.

Relay 3 switches resistors in and out in the high voltage power supply. It could also be that the power supply filter caps need replacing (although they are not that old, the earliest board I have seen is 1993).

Let me know if you need a drawing or pictures of the chassis.