I have joined the Dark Side (well not really)

[AdmiralB]

AdmiralB,
Since it seems you plan on making a habit out of arguing with most of what I say

That's because I disagree with a lot of it, and regardless of whether you're the "old-timer tech guy" here, you're not guaranteed to always be correct.

Suppose, like several Bass 400 and 400+ owners here, you discover those "settings" that Mesa specifies for tube bias are wrong.

I would always recommend that idle current be checked. HOWEVER, Mesa's approach is sensible, if also somewhat mercenary. IF their tubes are matched to a standard (and they are), AND the amp is constructed to that standard (and they are), then...the tubes will work. They might not be set to 'optimum', but then 'optimum' varies based upon what the player wants out of the amp.

The only issues I've seen is that Mesa's standard hasn't stayed...standard. If you put a new pair of their Chinese 6L6s, say, in a Mark II, they'll be way too cold. And if you put a set of old (but NOS) Mesa-matched Sylvanias in a new amp, they'll probably be too hot. But new Mesa tubes in a recent (i.e. post-1990) amp will work fine.

...and you conveniently left out that the amount of input voltage needed to drive a tube to full output VARIES with its bias (and plate and screen voltage, and load... )

I left nothing out. The input voltage IS the variable - the tubes are tested at a standard condition, and the input AC is increased until the tube clips.

Do YOU work at Mesa or GT? If not, then you probably haven't seen the devices. What I wrote was how Roy described it to me, if you have some knowledge that the manager of GT at the time doesn't, take it up with him.

yet there have been several stories of people here and elsewhere having bias related problems with Mesa tube bass amps BECAUSE the specs are wrong. And maybe, just maybe, some people would like their amp to actually put out power near its rating somewhat cleanly.

That's certainly possible, and I've given some examples above of how that might be the case. But I'll stand by my conclusion, which is that current Mesa tubes in a recent Mesa amp will work fine, and if anything err on the cold side.

Really, and why is that? Do you work for Mesa or GT? I guess you think it's better to just trash a perfectly good set of tubes because their bias current needs have changed rather than rebias them for proper operation, too. How often do you recommend that bass players change their power tubes?

Tell me, how many tubes have you seen age so that they draw MORE idle current? I've not seen ANY. As they age, their emmissive capabilities wane...so they require LESS bias voltage. Tubes 'age colder'...how is that going to 'trash' tubes?

You said elsewhere you were a guitar player, and you just told on yourself here. Bass players who use tube bass amps use them precisely to drive the crap outta them.

Yep, I'm primarily a guitar player. I've also played bass for quite a while. I've never met a bassist who played a tube amp on '10'. I've never heard one, either, except for Lemmy perhaps.

If you feel so strongly, will you warrant the amp for repairs for any damage incurred by using Mesa's rating system as a sole guide for tube replacement? Chances are, the poster with the question doesn't NEED new tubes anyway!

Mesa won't warrant the amp UNLESS you use their tubes. So what?

And yes, you're probably correct...he/she probably doesn't need new tubes.

 

[AdmiralB]

Also, the bias setting of your amp can drift. Not sure, but I think Psycho Bass Guy might have already mentioned this. It may need to be adjusted again.

How is this going to happen? Especiall in a Mesa amp - if there's nothing to adjust...how is the bias voltage going to drift?

 

[Rob Mancini]

I think he means the tube's bias voltage will drift.

 

[AdmiralB]

I think he means the tube's bias voltage will drift.

The voltage won't drift, unless the components in the bias circuit change. This can happen, but it takes a looong time.

He might mean that the tubes' voltage requirements for a specific idle point might change - and he'd be correct. Except, he said this:

Tubes do not set, nor do they have anything to do with the bias of your amp.

Which is kind of an odd thing to say. It's sort of like claiming that the strings on your instrument have nothing to do with intonation.

 

[Rob Mancini]

The voltage won't drift, unless the components in the bias circuit change. This can happen, but it takes a looong time.

He might mean that the tubes' voltage requirements for a specific idle point might change - and he'd be correct.

Yeah, that's what I meant. I just don't know how to say it like you techies.

 

[Frankie Fender]

*unsubscribed*

 

[Psycho Bass Guy]

That's because I disagree with a lot of it, and regardless of whether you're the "old-timer tech guy" here, you're not guaranteed to always be correct.

I fully agree that I can be wrong, but in this and the other cases with you, I'm not.

I would always recommend that idle current be checked. HOWEVER, Mesa's approach is sensible, if also somewhat mercenary. IF their tubes are matched to a standard (and they are), AND the amp is constructed to that standard (and they are), then...the tubes will work. They might not be set to 'optimum', but then 'optimum' varies based upon what the player wants out of the amp.

Nice dissemmination there. Most folks, myself included, view "optimum" as maximum potential, and for bass, that means 'maximum clean power,' which you don't get without a proper bias setting.

I left nothing out. The input voltage IS the variable - the tubes are tested at a standard condition, and the input AC is increased until the tube clips.

...and if you change that bias, the entire transfer curve changes. You're playing word games again.

Do YOU work at Mesa or GT?

I notice you neglected to answer my question. Does that mean you're another "undercover" shill poster like a few other manufacturers employ here?

Tell me, how many tubes have you seen age so that they draw MORE idle current? I've not seen ANY. As they age, their emmissive capabilities wane...so they require LESS bias voltage. Tubes 'age colder'...how is that going to 'trash' tubes?

Easy: they get thrown away by people who think their tubes are "worn out" when all they require is a simple bias adjustment.

Yep, I'm primarily a guitar player. I've also played bass for quite a while. I've never met a bassist who played a tube amp on '10'. I've never heard one, either, except for Lemmy perhaps.

You REALLY like splitting hairs and playing word games to dance around the inconvenient facts just to argue, don't you? Master volume settings have little bearing on actual output, especially with the wide range of output voltage available with basses.

Mesa won't warrant the amp UNLESS you use their tubes. So what?

You present yourself an expert on amps, handing out advice for others as to what they should do with theirs in regards to operation and repair. My advice is always to let a qualified tech check out any questions firsthand. Yours seems to be to just buy spare parts and install them at will with little to no regard for their effect.

And yes, you're probably correct...he/she probably doesn't need new tubes.

...yet you still felt the need to put up multiple posts where you obfuscate and twist the things I say!

It would appear I've found myself a new t***l buddy!

 

[AdmiralB]

Nice dissemmination there. Most folks, myself included, view "optimum" as maximum potential, and for bass, that means 'maximum clean power,' which you don't get without a proper bias setting.

I'd agree with this. However, how are you going to determing that point? In practice, the preamp or PI of any amp is going to clip before the power tubes...are you implying that a REAL tech is going to set the amp up on a dummy load, inject a signal into the power tubes (bypassing the phase inverter), and twiddle the bias whilst looking at the output wave on a scope? Get real, most techs are going to set the bias to some arbitrary percentage-of-maximum-dissipation and call it a day.

And that's about 100% more than any amp tech did until Al Gore invented the internet.

...and if you change that bias, the entire transfer curve changes. You're playing word games again.

Absolutely correct. Who said anything about changing the bias, though?

I notice you neglected to answer my question. Does that mean you're another "undercover" shill poster like a few other manufacturers employ here?

I'm not employed by anybody in the MI industry. I happen to think Randall Smith is an *******, FWIW, and many of his designs are classic examples of 'screw with it and hope it works'. But I don't think that's germane to this discussion.

Easy: they get thrown away by people who think their tubes are "worn out" when all they require is a simple bias adjustment.

In this case, I misinterpreted you. I thought you meant that the tubes would be 'trashed' by improper bias setting. However, how many techs are going to measure the idle current in an amp, find it lower than desirable, then tell the owner that he needs new tubes - rather than simply adjust it? I'm sure there are some like that out there, that has precious little to do with Mesa's practice of matching tubes and setting a fixed bias, though, eh?

You REALLY like splitting hairs and playing word games to dance around the inconvenient facts just to argue, don't you? Master volume settings have little bearing on actual output, especially with the wide range of output voltage available with basses.

I'd say it's you that's engaging in those behaviors. Who said anything about master volumes? I'm simply saying, I don't know any bassists who run their amps fully clipped. You implied that that's the only reason bassists use tube amps at all.

You present yourself an expert on amps, handing out advice for others as to what they should do with theirs in regards to operation and repair. My advice is always to let a qualified tech check out any questions firsthand. Yours seems to be to just buy spare parts and install them at will with little to no regard for their effect.

This is complete BS. I've presented myself as nothing other than a viewpoint which happens to disagree with much of what you've posted as fact. I haven't advised anyone as to what they should do with anything, and I challenge anyone to illustrate where I did.

The question was asked "should I buy Mesa tubes", and you said "no, you should not". That sounds to me like telling someone what they should do.

I said, "buying those tubes won't hurt anything". And I stand by that.

It would appear I've found myself a new t***l buddy!

Whatever.

 

[Chef]

PBG: thanks lots for your help.
Again, I'm back to loving my 400, thanks to you.

However, I'm outta here.

 

[Psycho Bass Guy]

However, I'm outta here.

You're not the only one. The motives for the last few 'posts in question' should be obvious to anyone, so I'm not going to worry about arguing. As I said before, EVERYONE who has tried things the way I've proscribed has been very satisfied. Troll feeding time is over.

 

[Stay Gold 1337]

okay so i got a 12AU7 for my 400+, but i was wondering if i should have a balanced one. the eurotubes retube set comes with a balanced 12AX7, something because it's the phase inverter and they're supposed to be balanced.

 

[Beefbass]

You're not the only one. The motives for the last few 'posts in question' should be obvious to anyone, so I'm not going to worry about arguing. As I said before, EVERYONE who has tried things the way I've proscribed has been very satisfied. Troll feeding time is over.

+1

 

[Psycho Bass Guy]

okay so i got a 12AU7 for my 400+, but i was wondering if i should have a balanced one. the eurotubes retube set comes with a balanced 12AX7, something because it's the phase inverter and they're supposed to be balanced.

A "balanced" driver tube is not necessary, nor is it necessarily superior to a "standard" tube.

 

[Vanni]

Ok guys,
I’ve been playing with my mesa for a month right now.

My 400+ needed a full retube, the power tubes was unbalanced, so I bring it to my technician.

He put 12 Sovtek 6L6WXT+, and gave me a couple of pre tubes: 4 tung-sol 12AX7, my old mesa and sovtek 12AX7, and a EH12AU7.

We tried the Boogie with an SVT810 with Tung-sol 12AX7, than with my old tubes (a Sovtek 12AX7 LPS, and 3 Mesa 12AX7). With the tung-sol I soon noticed there was a little more gain than Mesa pre tubes, and the sound was growlier and aggressive. With mesa the sound was so smooth… smooth, warm and balanced. Than we put back the tung-sols with the Electro-Harmonix 12AU7. There was a decrease of gain.

At home I tried some pre tube settings.

With the tung-sol, even with the EH 12AU7 driver, the sound was aggressive, an less defined on the lows, it remember me more the old mesa character, before the full retube (BTW the retube of the power amp is a big improvement, my amp sounds a lot better with all pre tube settings).

With old pre tubes the amp sounds smooth, warm, balanced and more defined. Putting in the 12AU7 the sound is cleaner, tight and defined in the lows, the mids and the highs are very musical… I can even use the highs control! Before the mods I have to set the pot at less than 1, now the control is a lot more usable, the highs sounds very musical! The amp sounds also bigger, fuller, thicker, balanced, punchier… D and G strings now sounds balanced and thick, just like E and A strings!

After all tests, my favorite pre tubes are the Sovtek 12AX7 LPS in V1, two Mesa 12AX7 in the other stages, and the Electro-Harmonix 12AU7 for the driver tube. Also, a BIG improvement is the new power tubes (Sovtek 6L6 WXT+), perfectly matched and tuned.

I found the new production tung-sols are not very reliable, with all the tubes switch, two tubes died… (BTW My technician advise me that the new tung-sol are not reliable).

To me, the “rules” to have a great sounding 400+ are 3 (as reported by PBG and Anderbass):
1) Adjustable bias mod, to tune perfectly the power section.
2) Stay away from “high quality” pre tubes (not true with my dying tung-sols ), keeping mesa pre tubes or similar.
3) Use 12AU7 for the driver tube.

I'd like to thank PBG… Thank you, thank you, thank you!!!

Ciao!!

Vanni

 

[Big String]

Hey All especially PBG
Recently I was thinking of revisiting an all tube amp (that I'm somewhat familiar with). I can probably re-purchase the 400+ I bought new a few years back from my local buddy. He's never gigged it out. I'm unsure of a few things and wanted to pick brains.

1. Can't find the dimensions and spec. ??
2. Can I use one 4ohm and one 8ohm cab together ?
3. What is the actual output, I know it's not 500w ??
4. Anyone put speakon connectors on their 400+

I remember that when hooking up two 8ohm cabs you plugged the speaker cables into the two 4ohm jacks since it would be a 4ohm load. (kind of unintuitive to me..) And likewise if using two 4ohm cabs you'd plug them into the two 2ohm jacks. Ok what ever...

Hence my question about using two cabs with different impedence. Are tubes amps ok running at 2.67 ohms like SS power sections ? Would I simply plug them both into the 2ohm jacks or have to choose a 2ohm and 4ohm jack ?? Possibly daisy chain the cabs.. ???

Just to mention my intention .. ha
One of the most sonically pleasing rigs I've ever owned was a Mesa Diesel 1x15 EV and my 400+ loaded with Svetlana 6L6GC and EH 12ax7 tubes. I am playing Dr. Bass cabs and they remind me of how full range and clean the EV cab was and I'm thinking the 400+ would sound great matched up with the DB's.

 

[anderbass]

1. Can't find the dimensions and spec. ??
2. Can I use one 4ohm and one 8ohm cab together ?
3. What is the actual output, I know it's not 500w ??
4. Anyone put speakon connectors on their 400+

(1) The 400+ is a 4 rack space amp thats about 12-1/2" deep by 19' wide. It weighs about 45lbs.
Here's a link to the manual:
http://www.mesaboogie.com/manuals/Bass 400 Plus.pdf

(edit)
Heres some links to more Mesa web site info relating to the 400+:
http://www.mesaboogie.com/Product_Info/Product_Guide/product_guide.html
http://www.mesaboogie.com/Product_Info/TubeReference/TubeRefGuide.html

(2) You can, I'd suggest connecting both these cabs to the amps two 4ohm speaker taps. (your 8 ohm cab will end up receving less power than the 4 ohm, and be a bit quieter in this pairing situation)
Here's why I suggested using your amps two 4 ohm taps:

This is in the FAQ, but there is a lot of stuff to dig through there. I edited and expanded it a bit so it ought to clear up a lot of the myths surrounding tube amps and speaker loads:

To understand WHY tube amps don't like higher impedances and why they are MUCH more dangerous to tube amps than lower ones, you have to understand what it is in both types of amps that actually does damage.

In solid state amps, the output transistors are connected directly to the speaker load. Amps put out a constant voltage and the varible that determines power/current is the impedance of the load. Ohms law: P (power)= i (current)/r (resistance). The lower the load (resistance), the greater the amount of current is passed.

Current also generates tremendous amounts of heat, which is why if the load is too low, the heat stress on a solid state's output transistors can damage them. The same rules apply to tube amps, but there is a deciding factor that makes a huge difference. Tubes are extremely high impedance devices, and in order to be connected to a speaker, must be coupled through an output transformer which takes the high voltage/low current output of the tubes and makes a high current/ low voltage output that can drive a speaker. Instead of being constant voltage amplifiers, they try to be "constant power" amplifiers; each tap of a tube amp's output transformer is wound at a voltage/current ratio to supply equal power to each of the taps of differing expected secondary impedances.

A transformer is an inductive coil that works by amplifying current and/or voltage. If the transformer is not connected through a circuit on both its primary and secondary taps, it will feed back on itself and generate a large voltage spike at its connected end. What happens with too high a load connected to the transformer's secondary is that it acts like an open connection and causes feedback within the transformer. Since the primary of the transformer is connected to the plates of the output tubes, this voltage spike hits them first. As long as it doesn't exceed their limit, you're OK, but if it does, you can short them, which WILL destroy your amp.

The reason a lower impedance is not so dangerous has to do with the nature of the tubes themselves. If the transformer secondary is connected to a lower than expected impedance, the transformer obeys Ohms law and tries to maintain a constant current to a lower load for an increase in power, but this causes a drop in the voltage of the plates of the tubes and they emit less, so power actually decreases, but because more current is flowing through the tubes, they get hotter and "age" their cathodes at a much faster rate than normal.

(3) My 400+ has around a 270 watt output before distortion sets in. Mesa's 500 watt claimed power output is a peak rating.
Here's some info about that:
http://www.talkbass.com/forum/showthread.php?t=283409

(4) Someone started a thread a while back proposing the addition of Speakon jacks on a 400+. I believe it was determaned that there wasn't enough room inside to do so in the origanal 1/4" speaker jack locations. I'd suggest just purchasing/making some 1/4" to speakon speaker cables if your cabs wont accept 1/4" cables.

 

[Tim1]

Aha! My favorite and most useful Talkbass thread of all time still lives. This has reminded me that I must take out the first three JJ preamp tubes I put in (but leave the JJ12AU7 mod) and try it with the mesa pre tubes again. My 400+ is a recent one so I do not know whether the Mesa pre tubes would be preferable to JJs as they are probably not the Chinese ones which PsychoBG recommended from the original models.

 

[Big String]

Hey Ander thanks so much.
Not to dispute your recommendation but wouldn't my 4ohm cab need to go into the 2ohm jack ? I can see the 8ohm cab going into the 4ohm ?? Maybe not. Before I offer to buy back the amp I want to make sure is all.
Thanks very much Sir!

 

[anderbass]

wouldn't my 4ohm cab need to go into the 2ohm jack ? I can see the 8ohm cab going into the 4ohm ??

Psycho has warned against simultaneously using two different ohm speaker taps on the 400+ serveral times over the years. You'll find two references in these threads:
http://www.talkbass.com/forum/showthread.php?t=127620
http://www.talkbass.com/forum/showthread.php?t=221491
(you could also Daisy-chain both your cabs into one of your 4 ohm taps, the amp would have the same combined cab load with this method too)

 

[Big String]

Ok cool I now understand about the 'taps' makes sense.

So... 4ohm jacks for both cabs or daisey chained into one of the 4ohm jacks for safety reasons. I'm just not completely understanding why as either way it's a 2.67 load which is below 4ohms.

And btw, I happen to have schematic of the 400+, I'll try an scan it. I had Mesa send me copies a few years ago when I was concerned about Phantom 48v messing up my amps via D.I. XLR out to the mixer. There does not seem to be isolation for the transformer if I remember correctly. My Mackie 1604vlz's XLR buss cannot isolate the individual channels from Phantom which we use for our horn's condenser mics. Since I was close to the board I just ran a sheilded cable into the 1/4 line which dose not see the 48v.