TC50 Tube discussion

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That is difficult to determine. I personally did not like the STR447 EL34 when I first took the TC-50 out of the box. At first it was overly bright and lacking midrange. In about 2 weeks of playing (depends on how long you play) I noticed a differences. However when I switched over to the 6L6 tube to try it and then to 6V6 for a while, after returning to the stock tubes they sounded better. All tubes will change in their characteristic from the time you first heat them up and play the amp and they continue to change until they are due for replacement. Generally the characteristic change is not dramatic as it is gradual. Any sudden changes (tone loss, no bass, no treble or the obvious no sound) would indicate time to replace or tube may have been out of its operating range and would ultimately quit or end up red plating.
Hmm. Sort of done but not happy with it. Had to pull out the mixer and use that verses direct to the Tascam recorder. I was loosing a bit of detail with the compressor on the front end of the Tascam so a better mic preamp did the trick. TC-50 and Vertical 212 cab. Top speaker at mid point of cone (at 15 degree offset Sennheiser e609, bottom mic Audix D2 pointed at center cone, for stereo detail and to capture the room, A pair of Audix ADX-51 at 90degree angle with apex pointed to speaker cab, distance of 7 feet. Guitar Kiesel DC600 with Graph Tech Licensed Floyd Rose with the ghost piezo pickup. I sort of ran the sequence starting on the clean channel normal with the piezo bridge, changed to neck pickup for some sloppy something, changed to drive mode and continued the what ever it is, changed to neck pickup and played a portion of the "Nobody's fault but my own", Led Zep. CH2 normal "Whole lotta Rosie" ACDC (ad-lib), CH3 something heavy I made up a while back. I repeated the process with each tube and left in the mistakes. Practice run was always great, hit record and you mess up. Enjoy it or hate is what it is...Never claimed to be a good guitar player.....You get the ideal how each tube sounds but to be fair I should have adjusted the settings on each channel to favor the tubes in use but did not. If you cannot make out the picture the settings are: based on the hour hand on a clock face (relative position).

CH1: P1:30, V12:00, G2:45, B11:00, M1:00, T1:45
CH2: P1:45, V2:30, G12:45, B2:45, M2:00, T11:00
CH3: P11:15, V2:00, G1:00, B1:15, M1:40, T11:45

There is some differences but not all that noticeable in the recording. The KT77 were abused in the Mark V first for a few months of heavy use. Ruby EL34BHT never got used since one tube was damaged (have three that are good). The NOS Siemens EL34 tubes are taking over as they keep sounding better. I did not include the =C= or the Tung sol tubes.... I did post comments so if you hover your mouse of the small icon just below the sound waveform the comment will appear. This will help you jump around between two tubes... I can sort of hear a slight hint of fizz but did not record well.
What I should have done was gone for a better tone for the Clean + Drive. Maxing out the gain really thickens up the tone for Led Zep and for ACDC but since It was dialed back a bit, I used the CH2 for the ACDC. I may get to the 6V6, and 6L6 variety later on. May even pull the =C= and Mullards out of both RA100s and where to go from there.... Where I found the most differences was with CH2. In some respects I would agree it sounds thin relative to the CH3 character but yet it is not. However I did notice a definite volume difference between CH1 and CH2/CH3. This got me thinking on rolling in some preamp tubes on the CH2/CH3 tube positions (V3 and V4) which has the same A/B assignments as the RA100 (V1 and V2). It is obvious they do not share the same layout but still share separate tube circuits for CH2 and CH3 and totally independent Clean channel. (you can literally remove the two clean channel tubes and it will not affect CH2 or CH3). In other words, if the same preamp tube tricks work in the TC-50 as they do in the RA100 even better. For some reason the TC-50 is not the beast I would expect it to be. Not that it is bad as I like it the way it is but I think it can be enhanced with just two preamp tubes, but what will do the trick is the question. I would prefer to remain stock but too late now..... The Mesa NOS Siemens are not stock tubes. They are definitely making me rethink the tube order of what I prefer. Also since I changed rooms with the amp, things changed in temperament of what I was hearing. Perhaps it was the reverberating drum set. I should have covered it with a blanket after disengaging the snare wires. I was comparing the actual to the mic'd signal though head phones, it was notably different. One the recording alone I would find it hard to decide what sounds better as all 4 sets of tubes sounded the same to me. That was not the case with the live signal though. KT77 still sounded better, Ruby was not bad but just a bit different in tone and the Siemens was just smoother than the Stock Mesa tube with some added aggressiveness like the Gold Lion and Ruby.

Time to rethink my strategy and decide if I need to redo the project again... I have yet to run this amp though the load box or even try the cab clone (not sure that will reveal power tube differences).
This evening I did manage to find time to roll in some preamp tubes in V3 and V4 to see if CH2 and CH3 can be tuned... I was unsure if the manual was correct as I thought the Clean channel was getting manipulated so I pulled V1 and V2. Manual is correct no clean channel but still had CH2 and CH3.

It did not matter what I put into V3 or V4 as the amp basically sounded the same. Ran though Tung Sol, Mullard (CV4004 and long plate 12AX7), Svetlana, Beijing 12AX7a, JJ ECC803s to name a few). I did not try the JAN/GE 5751 as I thought it would make the two channels brighter. I did attempt the JAN/Phillips 12AT7 in V4 which is the drive or 2nd/3rd gain stages (depending on channel) and the tone stack. Not much of a change there either. Perhaps the RA100 has a different preamp circuit as I was able to manage altering the tone a bit more. The TC-50 just sounded the same (except with the 12AT7). Perhaps it is due to a late tone stack as it is driven by the 4th gain stage of CH3 and the 3rd gain stage of CH2. Just a note the tube that was in V2 seemed to be the culprit why there was a dramatic volume difference between the CH2 /CH3 compared to CH1. I did got though my Mesa tubes and found a good one. No big deal, amps sounds great no matter what you put into it as long as it is a good tube. Other tubes I did not try were the Preferred series 7025 or the Northern Electric 12AX7 (better reserved for Hi Fi than guitar amp). In short it is not anything like the Mark V that responds well to preamp tube changes. The preamp is tight in its design so it will be harder to alter the tone or gain characteristics if you are looking for something different. Use a multi band EQ in the loop if you need to dramatically change tone. OD pedals seem redundant on the front end as the actual preamp sound better without them. actually the grid slammer has the same effect as the tight switch. I have also figured out that a drop in gain below noon actually sounds great on CH2 as well as CH3.
I bought a sextet of EH6CA7s, but have yet to try them in my TC50. I just can't get away from the 6V6s. I will say that I really liked 6CA7s in my V, though. I will be putting those back in that amp once I get the gain issue resolved.
The 6V6 is a fun tube in the TC-50. The only reason I took them out was to run the RA100 in parallel with the TC-50. Wow that was an experience. I have thus paired the TC-50 with the JP-2C, Mark V and Roadster. I am finding that the amp blends quite well with the other amps running with 6L6 (except for the RA100). And then this thread and why I volunteered to run through the tubes I have is still undetermined. I guess I had to know for myself what the end result was going to be.... Perhaps this weekend I will get a recording of the 5881 and the standard Mesa 6L6. 5881 are a better Mesa Alternative to the STR440 tubes. Thinking on getting another pair so I can run them in the Roadster.
I listened to the recording I posted again.... it sounds like crap, almost tunnel like and it is missing something (like the true tone I hear when I play the TC-50). It almost seems like a waste of time as all tubes sounded no different than the stock tube. That is not reality. Perhaps it was my predetermined settings as they were not ideal. I think I need to do it over again and perhaps use the manual to dial in the channels. Or dial in something that sounds better. Too bad I do not have a ribbon mic. I could opt to use the OS Recto 412 if that would help separate the tonal differences between the 4 power tubes. Sorry to those that listened to that recording. It was not helpful to me if I had not heard it before. My apologies. Perhaps using all 10 mics for the drum set and everything else in the mic locker may reveal a difference. Then again I have not pulled out the attenuator either. May give that a trial. Wonder what the cab clone sounds like (may as well find out). May look in my stash of tubes and replace a few with fresh Mesa tubes. It would not be the first time I found a bad preamp tube in a new amp. Usually the PI tubes are the weak link as they tend to be of lesser quality..... I will also use a different guitar (that does not have an active preamp in it so I will omit the piezo part, perhaps practice the songs I intend to play if that would help any).
My sound guy LOVES the Cab Clone in the TC50. Granted, I am only playing clean, but he raves about the Vintage setting. Keep in mind what Authorized Boogie said about the cab clone, though: try to match the EQ curve of your preferred mic to get the best tone. Personally, I have no clue how to do that. One thing I have noticed about the Cab Clone is that the tone is much brighter than my speaker, regardless of cab. At least, that's what I hear from the monitors and mains.

Just ordered a pair of the 5881s. Those will probably get used before the Gold Lion KT77s since the 5881s are Mesa branded and won't void my warranty.

I was almost on the cusp of selling my TC. Hard to believe, but I had a brief moment of "what do I need so many amps for?" Then I had a friend play the amp through a vertical 2x12 recto cab, and I realized there was no way I would ever sell this amp. It does everything I want and need. Now I just need to get my V in the same shape.
I would admit the Vertical 212 is awesome. To me that is the reference tone I am after. Perfect for the TC-50 and the JP-2C. The Mark V would be included in that as well. If you have a long head like a Rectifier or RA, the Horizontal is also a great choice. It is a bit awkward to pick up and move due to the single handle but works and sounds as great as the Vertical 212. At the moment I am running the JP-2C though the horizontal cab (it looks so small sitting there and at first glance you would think it is a Mark V:25). JP-2C is the smallest head I have but packs the biggest punch.

I would try different settings with the TC-50 as you might be amazed how it sounds with a reduced gain on CH2. The TC-50 like many other Mesa Boogie amps, it is all in the tone controls and settings (as I am learning).
Well...I just found, and bought, a vertical 2x12 for 450. Only bummer is that one of the V30s was replaced with a G12M-70. I have a sneaking suspicion I will be ripping that out and replace it with a WGS speaker. No matter, though. I now have a different Mesa cab than my RK 2x12. It's about time!
I would love to hear comparison of the stock EL34 vs. 6L6 vs. 6V6.
I'm not sure I like the stock EL34, looking for a more aggressive crunch American type on the mid and hi gain channels, maybe the 6V6 will do the trick?
Running now through a 4x12 OS, its sounds good but I'm looking for more "power" in the sound…
So, if any of you guys have all 3 type of tubes and willing to record something to hear the difference, it will be much appreciated.
I was thinking of getting a recording done with the 6v6 and the standard Mesa 6L6 STR440 but I prefer the Mesa 5881 STR 425. I have all the tubes on the Mesa page except for the KT88 (do not use that in the TC-50) or the EL84 (no place to put that in the TC-50 but will fit a standard 12AX7 socket, that would not work so do not try it).

if I get around to recording again, I will include the big three common Mesa tubes you can buy from Sweetwater, and I will add in the 5881 I had to buy direct from Mesa (same with the Nos Siemens tubes). I believe the 6V6 will sound better though the Vertical 212 than the 412 but why not try it anyway. This time around I will not use a fixed set of settings, I will dial it in for each tube if needed. I may have something by late Sunday....

I was debating if I want to run the OS Recto 412 or the Vertical 212, May try both cabs so one may get the idea how the cabinets compare. Both will be stock Mesa cabs.
:cry: Perhaps the recording with the TC-50 will be on hold until I get the amp back from Mesa. I thought something was going on with the amp as CH2 was getting softer. Now I get nothing on all channels but a week signal. This was sudden actually as the amp was working fine the last time I used it. I did let the amp warm up a while as I was playing through the RA100. When the standby switch on the TC-50 was out of standby I heard what sounded like a dirty pot and then nothing. Just the hum of the amp and the power supply. I did the typical diagnosis, and thought it may be the PI tube or the 12AT7 in V5. Next step was to figure out where the issue is in the tube circuits. Note that I have not been using the footswitch only the mini toggle on the front of the amp. I plugged in the footswitch to see if that would make a difference. The amp sounds like it is on mute and this is affecting all three channels. When I was tube rolling I only changed V3 and V4 which is used by CH2 and CH3. Also had the Mesa NOS Siemens EL34 tubes in use. I was able to rule out V5 and V7 and the power tubes by using the FX loop return as the guitar input, turned on the loop via the toggle switch on the back and had a dummy jack in the send. All was good there. Actually that sounded really good for a clean channel alternative. Mater volume and reverb works (changing channels you get the different reverb settings used). Presence also worked for each channel when selected but I was bypassing the entire preamp section.

Next up is to determine if I have signal coming out of the send jack and use that to slave another amp. I did replace the 12AT7 with a new Mesa 12AT7 and still had the same issue. I am assuming it may be a switching relay or loose solder joint somewhere between the final dive stages at the summing junction and the 12AT7.

I will take a look inside for solder joint problems and probe around some of the resistors and check some of the bridge capacitors (signal pass, DC block). May even tap on a few relays. Not sure what is up yet but looks like the amp is going to meet its creator. Bummer actually I was going to compare it to the RA100 again as I moved the half stack next to where the TC-50 is. Rest assured, what ever the issue is, it was not caused by power tubes. Also the tubes I rolled into V3 and V4 have been used in my other Mesa amps so they were known to be good tubes (removed from the Mark V). It is probably something minor as I had a similar issue with the RA100 but that was caused by buildup of aluminum chips from the tube shields around the tube ceramic sockets. Not the case here as I found the PCB to be clean of contamination after removing the chassis to inspect. If I find the issue I will report back but chances are the amp will go to Mesa for analysis and repair. I think it may be a solder defect of sorts. Lead free solder can result in performance loss if there is any signs of tin pest on the parts or what would be difficult to see would be voids in the solder joint itself resulting in an intermetallic layer between the PCB and the component leg. I will do my usual inspection but do not have schematics to help isolate the problem. I can figure it out without them. :roll: (if someone could provide guidance to the FX loop circuit on the send side and what components are used to mix or switch the CH1 and CH2/CH3 circuits that would be helpful.

For the time being, it was nice to fire up the RA100, forgot what beast that amp is. Sorry for the delay in revealing the results between EL34, 6V6 and 6L6 (was going to include the 5881).
Wow! Sorry to hear that, Bandit! Must have been the day for EMG filled Strat started crapping out on me last night, too. Thought it was the battery, changed it, still sounded like garbage. I was using my V3M at band practice, so I hope it's not that amp. Must have been some weird electrical garbage in the grid last night....

One thing for sure, the TC50 is still under warranty and Mesa will make it right! I would not be surprised if it was a solder joint. Ever since they switched to lead-free solder, I've heard more and more incidents where the solder cracked, myself included. Good thing we both have enough amps to get us by in a case like this!
I am going to investigate just for S&G. At least the am is not overly crowded as some of the others.... If I cannot figure it out by visual or meter testing it will go for the proper care. Still have not ruled out metallic contamination just yet. I picked off a solder ball on top of one of the relays when I opened up the chassis to get a view on the screen resistors (bummer as you cannot see them as they are covered by another elevated PCB assembly). My first thought was linking the issue as a latent problem caused by other power tubes.. Not the case here.... Something between the CH1/CH2+CH3 circuits and the 12AX7. I did check the input cable from the jack visually. I will have to ring out the continuity once I open it up again.
I spend a few hours doing a visual and found three suspect solder joints. The input cable was suspect, and two resistors had minimal solder fillet (basically open hole on the top side). I had repaired the suspect solder joints by reflowing the solder joints with a small amount of flux and a needle solder iron tip. Status is the same, no sound on any channel. I figured it would not be an easy find. Now I will be checking resistors as well as some trace continuity. I should just ship it to Mesa for repair as that may be easier. The amp sounds like it is on mute. Not sure if it is related to the Midi control as one of the legends along the ribbon cable to the midi control board is marked as mute and another with mute strobe. I believe it may be a MOSFET that went. Oh joy.... That is easy to find actually if it is bad the channel is usually shorted to ground (for N-channel MOSFETS), if it is the usual JFET J175, that is a P-channel enhancement mode so it will behave similar to the N-CH MOSFET but will lack the intrinsic diode from Source to Drain.
:p That was an easy fix..... found the problem, it was a 39K resistor that opened up on the 12AT7 circuit. R105 if I am not mistaken. I had a few 29k half watt resistors, carbon film rated for 350V. :p Repair took a bit of patience. I had to go to work to replace the bad resistor. My solder iron at home was not suitable for the task, all of my tools, flux, solder wick (and best of all vacuum solder pump) suitable for rework on lead free solder. Easy repair with the proper tools. Installed all of the tubes and sure enough up and running. :p

What would cause a resistor to open up like it did without any signs of current or load stress could be a resistor defect. At least I know what to replace if the issue returns. Hopefully it is not an issue as there is another one of these resistors on the amp but may not be of concern as it appears to be one of the filter circuits (part of tone stack for CH3 I would assume).
Now it sounds much better.....Not as grainy as it was with the Stock Mesa EL34 tubes. Also plugged into the OS Recto 412 as I forgot what the TC-50 sounds like though that cab. :shock: Very nice.... I still like the Vertical 212 but the OS Recto just sounds aggressive. Almost puts the RA100 to shame (sort of). I will set up for recording tomorrow as I have to get ready for jam session at my friends house this evening.
for point of reference,,, if you are so tempted to try a 12AT7 in V4 do not do it. Not sure if that contributed to the open resistor or not. What ever the case may be, the problem I had was not immediate and I was using stock tubes when the fault occurred as well as prior to this issue when the amp was working fine. I believe the resistor that opened up was the plate resistor on the send side of V5 which is a 12AT7 tube. I did not touch this tube position until after the issue had occurred. I believe it is just coincidental at best. I had the Mesa NOS Siemens EL34 tubes in the power section. This did not contribute either based on the location. Could I have accidentally plugged the speaker cable into the Send Jack? probable, but not likely as I double check before powering up but would explain things if I did, and the last time I used the TC-50 nothing was changed with any cables on the rear panel. I did check that after the amp did not work. At least it is repaired and running as good as new. Easy fix and will find out how well the part holds up to several thermal cycles. (usually the case that may cause micro fractures of the resistor element if there was a manufacturing defect of the part in question. That can happen so I am not upset by any means. Oh yeah, I did compare the RA100 again to the TC-50 after it has been broken it with the stock EL34 tubes it shipped with. The TC-50 has become more impressive and is more aggressive than the RA100. Both had a slightly different tone but similar. Depending on the gain setting on CH2 of the TC-50, it is similar to the Vintage Hi channel on the RA100. CH3 definitely has more gain and detail than the RA100. All is good. Will try to get something going to day with comparing stock EL34, optional 6V6 and the two Mesa 6L6 tubes (STR440 and the STR425 which are both current production tubes) with the OS Recto 412 cab.

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