NOS 12ax7's in MKIV

[Lights Out]

I just got a bunch of NOS Preamp valves from a Amp Builder friend

Some old Telefunkan from 1950's !, Sylvanias, Mullard , GE's
Amperex etc. And some GT Mullard copies

Im trying them in my Boogie MKIV

I dont know much about the gain structure in these amps, So far Im just experimenting with the V1 stage .

So far there I havent noticed a great difference in the few I have tried
Though the GT's seem to give it more Marshall, Soldano type compression which Im liking.

My question is what function *importance* (in gain & tone)
do the V1,V2 & V3 have in this amp & are they as prominent as the V1 ?

 

[Boogiebabies]

The V1 is the input stage and is very important as is send the signal through the entire preamp. The V3 and V4 are your lead gain stages. These will effect you lead tone. The V5 is the phase inverter and IMHO is as important as all the rest. The V2 is for the effect loop.


Note: There is a schematic available online that I do not know to be accurate where it states the V3 is the entire lead tube and V4 is for the reverb and is a 12AT7. Not knowing what year and version of MK IV you have will help in directing you to what expiriences we have had with tubes in our MK IV's.

Check your owners manual, or look for a tube function sticker inside the cabinet. My 12/93 MK IV has the lead and reverb circuit shared like the old IIC+ on the V3 and V4. I have honestly never seen a MK IV with a 12AT7 dedicated to the V4 for the reverb.

 

[Monsta-Tone]

http://www.mesaboogie.com/manuals/Mark%204.pdf


Here's the link to the manual. It tells you what each tube does.


V1 & V5 will provide the most substantial changes in tone.

 

[AMG1]

I dont know.

I've yet to see any real benefit from using NOS tubes in modern amps.

Some tubes do seem to work better than others regardless of age. I think it a luck of the draw type thing.

Leave the oldies for the oldies.

OK I'll duck now as you all throw the rotten friut. Flame on if you have to.

 

[axwielding1]

As far as the lead channel, or for high gain applications, NOS isn't going to make a huge difference, except that they are built better, last longer, and may provide more power...
But, I've noticed big differences in the clean to lower gain tones. I replaced the mesa tubes in V1 V2 V3, with GT12AX7M's, and liked the complex mids. This past week, I located some RCA12AX7's and RCA 7025's. I put them in place of the GT's, and found the cleans to be chimier, and more balanced tone. I then pulled the str454 , str442 out, and re-installed the str415's.... ahhhh, heaven!
ax. :twisted:
a really good NOS 12AX7 in V1 would be good in any amp.IMHO.

 

[Lights Out]

Well I have been wondering the same thing about NOS Valves.
So I had to get some & try them out.

There is a subtle difference but I havent Cranked the amp , just played at lounge room volumes.
Are they worth it ?........Im not sure yet

I have some Old Tung-Sol & Westinghouse 6L6's on hold too
How much do the Power Amp valves effect the tone in a MKIV ?


Im undecided about going NOS . But one thing is for sure they were built better & would probable outlast current valves .
As for tone ...undecided

 

[zeppman]

Unless I have the amp cranked, I can't really tell a major difference when swapping power tubes, unless it is from 6l6 to el34..etc. Pre-amp tubes have a much larger impact.

 

[palomino]

I'm with Zeppman on this one. To me there's not a big enough difference in sound between new production or NOS power tubes to justify the cost.

I have found that pre-amp tubes are another story! I have some old Mullard and RCA 12AX7's that I use in my MK IV. I've noticed a big difference between these and new tubes like EH, Sovtek, etc...

Doug.

 

[Ken j]

I have some NOS GE6L6 "clear tops", RCA 6L6 "clear tops", and some RCA 6L6 silver top tubes. I also have some NOS RCA 12AX7 and 12AT7 tubes. I have used various of the 6L6s, in my DC-5, and IMO they sounded darker than the Mesa 420s in the amp. I wouldn't say one sounded better than the other just different. I haven't played around much with the preamp tubes in the Mesa but I have in a THD Univalve belonging to a friend. I did not care for the Univalve period so it didn't matter which tubes were in it. He has since sold it.

 

[Lights Out]

I have been swaping Preamp valves for two days.
This is a headache on the MKIV combo as Im pulling out The Power valves to get to the Preamp valves.

I have noticed some differences..Im only playing at Loud TV Levals.
Not Cranked , so there might be more difference at band volume
But the difference isnt that much.

I still might go for the NOS Power valves or even try out some KT-66's
Have anyone tried these in a MKIV