thinking on pulling out the OTR, back to stock

I have had the OTR speaker in the Mark V combo for a while. It does sound good, actually much better on the clean channel especially when using piezo pickups. I feel that the OTR had more of a vintage tone too it, a bit more than I would have expected. When pushed it sounds good but seems to have that blanket effect due to the top end roll off. May as well restore the 1x12 open back extension speaker with the MC90 while I am at it. I did not find the OTR favorable for use with the JP-2C (basically for the tone). Since I already have a loaded OS Recto 412 with EV speakers, it could not hurt to swap two out with the OTR speakers since they are similar. At least this will add some midrange to the cab as the EV black labels seem to be too flat in response in the midrange, bright at the top end and ok on the bottom. Also I thought the extension cab sounded exceptionally well with the MC90 in it. I can use that with the Mark V and or the TC-50 so no loss in having it. Also I liked the Combo with the MC90 when coupled to the horizontal 212 cab with the V30 as that sounded the best overall. Time to heat up the solder iron and pull the speakers. Also for some odd reason or another I am back to wanting to sell the V. Will have to see how things turn out with the speaker change. May also roll in some tubes too just for kicks. I get bored sometimes and that may be a bad thing. At least changing one or two speakers is easy to do vs trying to swap a loaded 412 (takes more time to open it up than change the speakers as it seems to reseal itself so doing the EV/OTR swap may be a bit more time consuming when I go to do it.)

Before I pull the speakers, may have another go as I still have an extension cab with an EV in it. Will have to hear the difference with those to blended. Not sure how they will sound mixed in a sealed cab though.

-

Thanks APEMAN.

So far I believe I favor the MC90 over the OTR speaker in the combo. Not that the OTR is a bad speaker, it is actually robust and would probably benefit some time in the OS Recto 412 with the EV speaker. 4xEVM12L black label tends to loose some midrange. Before I removed it from the combo, I did re-tube the preamp back to stockers. Blah. The 12AT7 has to stay in there. Just for S&G's I pulled out the oversized extension 112 cab that still has an EV in it and hooked it up with the Mesa 112 cab that had the OTR in it. Ran the Mark V and to my amazement that sounded great. Then the bright idea came to me, If and when I do get the TC100, where will the JP-2C go? Plugged it in to the two speakers and again, sounded like a blanket. The JP-2C is a bit darker in tone than the Mark V and the Vertical 212 cab just sounds awesome with that amp as does any of the 412 cabs I have. May hold off on the EV swap in the 412 cab but that should be a simple change over.

Go the MC90 I had bought for the combo installed. Dang it. definitely damaged the speaker when I restored the bias on the Mark V. The amp was pushing 150W peak, actually it was pegging the RMS peak meter on the Rivera Rock Crusher when I was trying to record with it. I also noticed the dust cap was removing itself from the cone. Yet another MC90 loosing its dust cap. I figured before it separated completely to re-glue it. I did run the amp with the MC90 in it for a bit sounded **** good except for the snappy vibrations on the dust cap. Oh well. I can order another MC90 (again). At least the one I took out of the extension cab was in excellent shape, never really used it. That is now installed and ready to go.

As it seems, every combo amp I ever own always gets modified to some extent. RA100 and V30 in an open or ported back just sounded fizzy, Celestion G12H75 Creambacks cured that quite well. Carvin V3MC went though many changes too, MC90 sounded great in that amp but now have Jensen Blackbird Alnico speaker in it since I tore the edge of the cone when installing it in the Mark V combo. Still sounds good even with the rip. Bummer. OTR just not for me sadly to say. When the fabric glue cures a bit I will fire up the Mark V again. I doubt I will sell the amp but at times I want to think about it.

Heads only please..... So when ever the next Mark comes out, it will not be a combo if I get it. Actually my Mark V was a head when I bought it but when the Roadster came to roost in my home, the Mark V got transformed and collected dust for a few years. I have put more effort in trying to understand the Mark V than any other amp. Since it is quite similar in topography to the JP-2C, it sounds so different (which may be a good thing because if it sounded the same I would have been disappointed, big time). Note to others, when recorded it will sound similar but in the real world you hear and feel far more than what you get in a recording.

I think the glue will work for the time being. I waited a few hours before playing again and did not hear the crappy slap with the low frequencies. Will see how well it holds up. This speaker got pushed a little hard before I removed it. Also had returned the bias back to where I had it as I do not what to go though tubes every 2 hours like I did after getting the amp. If it works, leave it alone. Bottom end is good, top end is good, midrange is present, amp sounds as good as it will get. Ready to sell if I so desire but doubt I will do that as I really do not want to go through all the trouble again if I miss the dang thing. Somehow I highly doubt I would miss it if I did since I have something else to jump on to if I what that iconic mark tone which actually does it way better than the Mark V. You guessed it, the JP-2C rules that category quite well. If I want crunch, just jump onto the TC-50 or RA100, heck just run them both at the same time. And then there is the Roadster collecting dust, need to bring that out and shake the house some more (JP-2C does that with ease as well), also have new tubes to stuff into it. I ordered a quad to replace the one's I have in the JP but got yellows. Bummer I was after grays but they did not have those. Those work well in the Roadster, should try them in the JP just for kicks. Did not want reds. Running the Greens in the Mark V, not bad.

May as well use up what is left in the KT77 before eating up any other tubes. So far amp sounds great so no rush in making any changes. For some reason, my Mark V is not normal, no magic or mojo to speak of. It is just OK. Too bad Mesa is using that as its flagship amp since they have made much better amps before it and after its release (even if the JP is based on a 38 year old design with a few modern tweaks. That is every reason to get one if you do not have one already!)

Will have to see how I like or dislike the Mark V once I get my hands on the TC100. The TC-50 is so much fun to play through and I can get lost for hours on end once I plug into it. The same goes for the JP-2C (I can get similar tone and character from this amp just by rolling back the guitar volume, sure may not sound like an EL34 amp but it just sounds so good).

How I rate it (which is just my opinion and may not be the same as yours)

JP-2C :shock: 8)
TC-50 8)
RA-100 8)
Roadster 8)
Mark V :roll: undecided (I can't believe you bought one :lol: how many speakers is that now? :lol: what were you thinking :lol: )

I am liking what I am hearing so far with the Mark V after going back to the MC90 speaker. I did not like that speaker for some reason or another with the Mark V combo. However a few things have changed in the amp that made the bond of the MC90 more pleasing. Removal of C39 from the V4B circuit. Sure the cap is there to prevent any unwanted oscillations due to the design of the gain stage having the highest gain ratio in the amp. There is a similar cap on V5A but that component has historic presence so I left it in place. Since the V4B gain stage follows the low gain overdrive stage, the coupled grid to cathode through the C39 capacitor also contributed to some midrange and moderate treble loss. Since this circuit has an extremely high gain for higher frequencies, what gets filtered out in the treble gets put back in due to the non-linear doubling effect of harmonics. This also acts to cut midrange to some extent which makes CH3 sound a bit thin and brittle. Removal of C39 reduces the upper midrange filtering which seems to balance out the tone of the amp. From what I have seen in older designs of the Mark Series amps, this particular gain stages does not have this grid to cathode capacitor but the remaining components are identical, cathode resistor, plate resistor, cathode bypass cap. The only difference may be in the plate voltage and input impedance to the next gain stage (which looks about the same as the older designs). I thing what sets the Mark V apart from its heritage may be in the tone stack for CH3. Any mods to that can wait for now. Another lesson learned, if you make a mod, only do one. I took the liberty to restore the bias back to its original state (or close enough). This definitely resulted in more power delivered to the speaker so when I installed the MC90 I almost blew it out as it did not sound like it would survive more than a few minutes of use. I did not realize at the time but when I hooked up the Rivera Rockcrusher to the amp I noticed the input was pegging the peak meter. Not sure how accurate it is but that would mean the amp was pushing 150Wrms. With the bias mod I made, it would only peak around 110Wrms. I did the bias mod in hopes to prevent instant tube red-plating. I had issues with this amp early on and for some reason Mesa tubes kept failing. I would not recommend any mods to the bias circuit in your amp. If you are not burning out tubes in a short time, leave the circuit alone. If you are having power tube issues, send it out for repair by Mesa or Mesa Certified Tech. So far my amp has remained quite stable after the fix. Before I made any change to the bias of the amp, the only tubes that would survive the stock bias setting in the amp were SED =C= 6L6GC. Since those are now scarce I needed another avenue to continue using the amp so bias reduction by a small amount seemed to work out and since then I was able to use the Mesa tubes for extended periods without red plating the center pair. I did check all component values for all of the power tubes and everything appeared to be in order. I do not have a bias probe to check currents and plate voltages on the tubes. However a gamble to change an 82.5k resistor to a 91k resistor paid off. It measured resistance is actually 89k. To get the gain closer to stock, I used a parallel resistor placed onto the 91k resistor and the measured result brought it to 83k. I did not red plate any tubes and use the amp for a few days this way, but in the process I damaged the MC90 speaker, dust cap broke free from its glue. Now that I have it back to where I fixed it with the 91k resistor, I figured I may as well give the MC90 another run in the Mark V combo as I never had a chance to try it with the C39 removed from V4B circuit. I can say I have more respect for the MC90 speaker now than before.

Played for quite a while last night and had some fun for a change. The dog did not like it as he took his favorite toy with him the second I reached for the power strip switch. This time I had the Mark V stacked on top of the Mesa wide body 112 open back cab and ran it parallel with the combo speaker. Having two MC90 stirring up the air was quite rewarding for a change. The preamp section is not quite stock although having the stock tubes in the amp was not all that bad. What works well for me is the Beijing Chinese 12AX7 in V1, V5, V6, Mesa 12AX7 tubes in V2, V3, V7 and the JAN./Phillips 12AT7 in V4. A quad of Mesa STR440 Greens and the good old EHx 5U4GB (same tube Mesa uses).

The Chinese tubes do tailor the tone just a bit but with the Mesa tubes in V2 and V3, CH2 remains about the same with plenty of rich overtones. Mark I mode is definitely deep in character but the midrange is still dominantly pleasant, jump onto crunch and it still has the soul of the Mark I but with a bit more edge and less bass dominance. Edge mode also sound OK, actually better than it ever did but that is one voice I do not use very often if at all. CH3 still has its reborn tone with thanks to the 12AT7 reducing the top frequency gain (low end gain remains the same as the 12AX7). That is what makes triode tubes interesting, since they are non linear devices, the gain characteristic is also non-linear over the band of frequencies. It is still a puzzle why this amp in particular is so different in its voice compared to the JP-2C, Mark IIC+, Mark IV, and Mark III which basically share the same driver circuit topography with the exception of where the GEQ is placed.

So why the pull on the OTR speaker? It has great qualities but with a driven source the top end chime gets eroded away. Still the speaker is bright enough to rip out some interesting harmonics, pinch offs, and the like. Its enhanced midrange coupled with the high end roll off filtered out some of the character of the amp that I was missing. It was quite more evident with an amp that is not overly bright to start with such as the JP-2C. That amp has more balance across the frequency range of the guitar that sounded like a blanket was placed over the cab when driving the OTR speaker with it. I am not done with this speaker as I have plans to put the two OTR in the OS Recto 412 that is sporting the EVM12L black label speakers. The added midrange will make things a bit more interesting. The only setback with the MC90 speaker is that it does not sound as good as the OTR on the clean channel when using a Piezo pickup. For a clean amp, the OTR makes more sense to have. So far it was the best performer and I would rate that above the Jensen Blackbird Alnico speaker (at the time I thought that was the pinnacle of perfection for a clean channel speaker).

I would say the Mark V is definitely ready for resale since it sounds exceptionally well at the moment. By no means does this indicate I will sell it but it has crossed my mind on several occasions. As I have found new enjoyment with the tired Mark V it would be difficult just to sell it as I still have a purpose to keep it. Recently I have been blending amps together as this adds more layers to my sound. It is sort of freakish how well this concept sounds. I decided to give the Mark V another go with the JP-2C. As it seems the CH3 IIC+ and the Mark IV voices blended extremely well with the JP-2C set to CH2. I found it interesting how well the JP-2C cleaned up with a reduction in guitar volume but the Mark V remained about the same. Definitely there is a difference in its touch sensitivity in signal response. Definitely a worth while endeavor to experience. Also, the Mark V blends extremely well with the TC-50 which is just as rewarding as blending it with the JP-2C. There still remains a lot of potential for the Mark V, just figuring out how to use it is the key to any rig.

My Mark V combo has got to be more than a test bed for speakers and what not. This is what happens with combo amps. I did install the OTR back into the Mark V combo but will be coming back out in favor of the EVM12L speaker I had in there before. Reason for the change, well the extra midrange of the OTR does sound good but in a single speaker combo I think I prefer the EV's flat response better. Since I have two of the OTRs I will be stuffing them in the 412 once I figure out how to remove the seal on the speakers. I was not planning on taking them out. Rubber tape tends to glue itself once compressed.

Back to EV and reason behind this was a mod I completed on the Mark V preamp and I want to take full advantage of that. OTR seems to color the tone somewhat just as much as the EV but differently. Both are great speakers but would like to see how the OTR performs in a 412 format with two EV speakers. Since I ran the TC-100 though the EV loaded 412 I noticed it was missing something so the extra midrange could help without dramatically effecting the tone. The EV black label speakers are very bright where as the OTR is not so the differences may even out. Sooner or later I may try something else like a Celestion copperback or other.