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I have joined the Dark Side (well not really)

#181
I believe I remember Psycho stating somewhere that the 2-ohm tap would probably also be just fine with the 400+ and a 2.67 cab load. (although I couldn't find his quote)

I take Psycho's ohm quote (above) to state that power tubes can get hotter, wear faster and sometimes fail due to using lower # ohm settings/speaker taps than your combined cab load... So I kinda choose to obey and recommend anything that may increase my powertubes lifespan.

I've heard the 400+ DI is transformer coupled and Phantom power has no negative effects.
Here's an older phantom power/DI thread referencing the 400+ that was never challenged:
http://www.talkbass.com/forum/showthread.php?t=242155

I haven't noticed any issues or difference when I've attempted to connect my 400+ DI to a mixer with global phantom power switched on.

I'd trully love to have a scanned copy of the 400+ schematics... :)
 
#185
anderbass said:
I believe I remember Psycho stating somewhere that the 2-ohm tap would probably also be just fine with the 400+ and a 2.67 cab load. (although I couldn't find his quote)

I take Psycho's ohm quote (above) to state that power tubes can get hotter, wear faster and sometimes fail due to using higher # ohm settings/speaker taps than your combined cab load... So I kinda choose to obey and recommend anything that may increase my powertubes lifespan.

I've heard the 400+ DI is transformer coupled and Phantom power has no negative effects.
Here's an older phantom power/DI thread referencing the 400+ that was never challenged:
http://www.talkbass.com/forum/showthread.php?t=242155

I haven't noticed any issues or difference when I've attempted to connect my 400+ DI to a mixer with global phantom power switched on.

I'd trully love to have a scanned copy of the 400+ schematics... :)
Click to expand...

Sorry for being sooo confused here... :rolleyes:
If I interpet that correctly (which I doubt because you recommend 4ohm jacks) wouldn't that be higher than my combined speaker load of 2.67 ??? I must be missing something or have it backwards.

DI: I could never get a straight answer from anyone on the transformer being protected from Phantom so I just used a 1/4 for my bass channel that was out of that buss as I was close enough .. less than 18ft .

Hope the schematics help.
 
#186
Big String said:
Sorry for being sooo confused here... :rolleyes:
If I interpet that correctly (which I doubt because you recommend 4ohm jacks) wouldn't that be higher than my combined speaker load of 2.67 ??? I must be missing something or have it backwards.
Click to expand...

Whoops, your right. I've edited my previous post.

I had meant to say "lower" and read:

I take Psycho's ohm quote (above) to state that power tubes can get hotter, wear faster and sometimes fail due to using "lower" # ohm settings/speaker taps than your combined cab load... So I kinda choose to obey and recommend anything that may increase my powertubes lifespan.

Thanks for posting the schematics, you did good!
 
#187
anderbass said:
(2) ... (snip)... (your 8 ohm cab will end up receving less power than the 4 ohm, and be a bit quieter in this pairing situation)
Click to expand...

While the 8 ohm cab may see less power, that doesn't automatically imply quieter (less SPL) sound. The actual performance of the cabinet (its drivers and efficiency, cab design, etc.) are highly crucial to what's louder.
 
#188
400+ using 1 each of a 8ohm and 4ohm cab.

I called Mesa yesterday to see what they had to say and they told me to hook the 4ohm cab to the 2ohm speaker out and the 8ohm to the 4ohm speaker out. I don't believe that is very safe from what I've been reading here. At first, I actually thought this would be correct until I got involved in this thread. Honestly the people I spoke with seemed quite unsure ... yikes. I'm sure it would work, but sounds like it would be tough on the tubes at least. Comments please.
 
#189
Big String said:
400+ using 1 each of a 8ohm and 4ohm cab.

I called Mesa yesterday to see what they had to say and they told me to hook the 4ohm cab to the 2ohm speaker out and the 8ohm to the 4ohm speaker out.
Click to expand...

It sounds like they're shooting for the Ampeg Customer Service Misinformation Award. IOW, that's a bad suggestion.

I don't believe that is very safe from what I've been reading here.
Click to expand...

It's not "unsafe" is the sense of immediate amp destruction. However it WILL cause serious premature power tube wear and an overall DROP in output power.
 
#193
anderbass said:
I took Psycho's advice and just got my 400+ back from my tech (fellow T/B member timv) yesterday.

Tim instaled an adjustable bias mod, two Chinese 12AX7's he'd tested/selected out of my stash of used spares (1 Groove tube 12AX7 and a Mesa STR SPAX7A), and then instaled a (quote) well balanced 12AX7 in the 3rd slot (JJ), and a well balanced 12AU7 in the 4th or left position. (older used tube that only seems to be labeled "USA 12AU7A")

(I believe I'm quoting my tech correctly here)
He stated that after the bias mod, my amp still only maxed out at around 270 watts (clean) due to its transformers limited capacity, but each side of its power section was now much better balanced and showed much less crossover distortion . He tested and found a surprisingly large variation in my two year old set of (Matched) JJ power tubes and arranged them into 2 groups of the closest matching sets, while exchanging one that tested much lower with a better matching JJ he had in stock. He also cleaned and tightened all my power tube socket conectors to better fit my JJ's power tubes somewhat smaller than normal sized pins. (I think I read somewhere that the newer JJ's power tubes now come with normal sized pins)

When I picked it up, he didn't really expect me to notice a huge improvement, but I definitely do.

Previously, my (fully) JJ equipped 400+ has always had me constantly knob twiddling in a futile attempt to tame its somewhat harsh upper-mids while trying to compensate for the comparatively thin sound I got while playing upper register notes with my basses.

The tone now is very rich, full and much more three dimensional sounding at nearly any imaginable knob settings compared to before. The upper register notes now ring out full and much thicker sounding, the harsh upper-mids are completely gone and the lows are allot tighter. It simply sounds better in every way.
I know the real test will be with my band. I've only spent a while trying out different combinations of preamp channels, tone knob and push-pull settings, but I honestly cant make this thing sound bad now, no mater how I set it.
Psycho already stated this, and I completely agree that my tone knobs are absolutely much more responsive with this different tube arrangement compared to my previous JJ's.
My Mesa seems to be a plug and play amp now, and I've always considered it to be anything but...
I'd highly recommend the bias mod and a similar tube arrangement to anyone not completely satisfied with their 400+.

The small panel in the center is the adjustable-bias pot board he built and instaled to a previously-existing mounting hole. (looks like its always been there)


153_5398.jpg


I'd like to thank both Psycho for his tips/PM's and especially timv for the wonderful job he did on my amp.
Click to expand...

No doubt, never give up on a tube amp until you've tried swapping/changing preamp or power tubes.
 
#194
lavaman67 said:
Tung Sol New Production 12X7s!

http://www.tubedepot.com/ts-12ax7.html

I spent about 4 weeks researching 12AX7s to replace the stock Mesa tubes in my 400+. Tung Sol's gave me everything I was looking for and everything you mentioned KJung. I also tried a Electro Harmonix 12AX7s and they were good too, but I ended up feeling better about the Tung Sols. The stock Mesa's were really bad. I think they were rebranded Sovtek WA's 12AX7s if I remember correctly. The difference was night and day. Were the Tung Sol's twice as good as the Electro Harmonix, given the price? Probably not. I would say the Tung Sol's gave me a little more clean headroom and seemed to be a little more warm and musical sounding. The EH's gave me a little more gain.
Click to expand...

Interesting. Sovtek, EH, and Tung Sol all made from same material, on same machines, by same people, in same factory. The EH and Tung Sol Tubes are identicle except for one part (the Getter).
 
#195
Just reading some of this. Cool thread. Makes me mis my 400 and 400 +.

I used a 6189 in the driver stage of both my amps. Must be something to this. Unfortunetaley mine were stolen a number of years ago. :crying:

I used a pair of road ready thiele 15 Cabs (EVM15L no tweeter) with the 400, a Powerhouse 4x10 and Powerhouse 2x15 with the 400 +. It was a wall of doom. I dont mis toating all that crazy stuff though. We used to play a lot of Outside Biker Gigs. :bassist:
 
#196
Big String said:
400+ using 1 each of a 8ohm and 4ohm cab.

I called Mesa yesterday to see what they had to say and they told me to hook the 4ohm cab to the 2ohm speaker out and the 8ohm to the 4ohm speaker out. I don't believe that is very safe from what I've been reading here. At first, I actually thought this would be correct until I got involved in this thread. Honestly the people I spoke with seemed quite unsure ... yikes. I'm sure it would work, but sounds like it would be tough on the tubes at least. Comments please.
Click to expand...

This makes perfect sense, seems how if you put an 8 ohm load into the 4 ohm jack it will pull half of the recommended load from the OT, and add a 4 ohm load into the 2 ohm jack, half recommended load from the OT, therefor 1/2 load pulled from 4 ohm tap + half load from 2 ohm tap = the full recommended loading of the OT

so it would be the exact same as two 8's in the 4 ohm jacks and so on
 
#197
This has comeup before and Psycho and other tube experts have advised strongly NOT to follow Mesa's advice on this matter. I read in another thread that Psycho is temporarily out of the forum, but IIRC his advice is to plug both the 8ohm and the 4ohm cabinets into the 4 ohm output jacks of the 400+.
 

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