Mark IV pre-amp tube question

[Aart]

Hello,

I have a Mark IV combo(small) with boogie logo, 1991, and the mesa site says there are 5 12ax7's in the pre-amp.

But on the chassis it says 4 12ax7's and one 12at7. is that normal?

Thanks,

Aart

 

[Boogiebabies]

Yes, it is an early MK IV known as the MK IV A.

 

[Antoine]

Yes, I've got a MarkIV Short Head from 1998, and i've got 5 12AX7, a friend of mine has a Long Head from 1992 and it has 4 12AX7 and a 12AT7 !
Mesa changed the 12AT7 phase inverter for a 12AX7 one, but i don't know when they have done it exactly, i think 1995/1996 !
I've tried a 12AT7 in place of my 12AX7 phase inverter but didn't like it at all, so i have keeped the 12AX7 !
I think amps built with the 12AX7 for phase inverter sound much better with the 12AX7 in this position, and amps made with the 12AT7 sound better with the 12AT7, but you can always try a 12AX7 as the phase inverter in yours and see if you like it better or not !!!

 

[Aart]

Well, i had a microphonic tube in the pre-amp.

And my tech told me that it was a 12ax7 where a 12at7 belonged.

What is the biggest differrence in sound between the mark IV A and the newer ones?

And are the A versions rare? It is an 230 V version(export).

 

[screengrid]

Hi all,
I'm new to the board and so it's my first post! First let me say, that I'm a big Mesa Boogie fan since a long time already. So my MK IV also is one of the early one's build approx. Dez. 1990. Serial Nr. is IV 0726 and I purchased the amp on 2.1.1991. The early MK IV's were build with a 12AT7 for the reverb stage. Also the tube configuration is a little bit different to the newer one`s. If you look for the tube task chart of the newer one's manual, you know what I mean ( Description of tube functions ! ) IMO, the older tube configuration offers the advantage, that it is easier to fix tube problems, because the tube functions/stages are not distributed over different tubes. Which means for example V4 ( V4a/V4b ) is the 12AT7 Reverb tube or V3 (V3a/V3b ) is the Lead tube. Beside some other small changes ( Effect Loop ) there are no big differences between the older and newer one's. Although some time ago, I heard some people telling, that with the older one's different ( better !?)output trannys were used. I never heard about MK IV A types, that is really new for me. As far as I know a MK IV C Top and Combo version was available around 1996, at least in Germany.
IMO, beside the minor changes with the newer one's one will not hear so big differences in tone. Of course the Custom 90 speakers used at time in comparison to the earlier stock 200W EVM 12 is a bigger one of change, tonewise. I use both speakers, in combination the best of both worlds, IMO!

regards :wink:

 

[Boogiebabies]

The MK IV B with the 12AX7 Reverb send and return came out late 1993 and also included a satellite send. The export version is very rare in the USA as it is not switchable like the old all world export transformers with the voltage tap switch. Your amp tech needs to read the MK IV A schematic on www.tubefreak.com where the reverb send and return is a 12AT7. The MK IV A has a lead channel that is identical to the IIC+ whereas the MK IV B has a few tweaks to the PI circuit depending on R2 or Lead mode and a minor tweak to the cathode of the V4A lead voicing. It is very minor. The PT's are different on the early ones. Yours should be a 561137 and is a bit larger than the 561136 and the 561140.

 

[Boogiebabies]

Hi all,
I'm new to the board and so it's my first post! First let me say, that I'm a big Mesa Boogie fan since a long time already. So my MK IV also is one of the early one's build approx. Dez. 1990. Serial Nr. is IV 0726 and I purchased the amp on 2.1.1991. The early MK IV's were build with a 12AT7 for the reverb stage. Also the tube configuration is a little bit different to the newer one`s. If you look for the tube task chart of the newer one's manual, you know what I mean ( Description of tube functions ! ) IMO, the older tube configuration offers the advantage, that it is easier to fix tube problems, because the tube functions/stages are not distributed over different tubes. Which means for example V4 ( V4a/V4b ) is the 12AT7 Reverb tube or V3 (V3a/V3b ) is the Lead tube. Beside some other small changes ( Effect Loop ) there are no big differences between the older and newer one's. Although some time ago, I heard some people telling, that with the older one's different ( better !?)output trannys were used. I never heard about MK IV A types, that is really new for me. As far as I know a MK IV C Top and Combo version was available around 1996, at least in Germany.
IMO, beside the minor changes with the newer one's one will not hear so big differences in tone. Of course the Custom 90 speakers used at time in comparison to the earlier stock 200W EVM 12 is a bigger one of change, tonewise. I use both speakers, in combination the best of both worlds, IMO!

regards :wink:

A few very good points, but all MK series amps take 265 (or more) Volts to the first plate in the lead channel and 423 volts(or more) to the first plate of the Reverb tube. Whether they are using the same two triodes in a tube is useless when you know what two are bound to go bad soonest. If the V1 goes bad it squeals. If the reverb driver or first lead stage go bad it sounds like a lot of white noise and no drive or no reverb. The MK IV B also has changes, although minute voicing changes and the loop was footswitchable. The OT should have been the same 562004 on all versions. If you have the number you can prove or disprove it as really erly versions like # 726 do not show up every day.

The PT is positively different and yours is uncommon period being an export.

Ed

 

[screengrid]

Hi Ed,

thanks for your quick response. You are right, my MK IV is a export model, powertranny wired for 220 V~! For fixing tube problems, basically of course it doesn't matter , how the the tube stages/functions are configurated. What I mean is, that it should be a little bit easier for a unexperienced user of a MK IV, especially if the user has now idea of electronics / tube technology. You seem to be more on the experienced side.
The plate voltage of my MK IV for the lead stage is 220V- at V3B and 265V- at V3A, 80 V- at reverb tube V4B and 320 V- at V4 A, at least according to the schematic I have. Honestly, until today I never needed to take the chassis out, all few problems I had over the long time of use were tube problems. The sound of the amp is still incredible, warm ,full and screamy without any hum , crackle or other strange noise!
Can you tell me a little bit more about the different MK IV versions until today, Mesa Boogie manufactured over the time? thats really very interesting for me, as already mentioned, I only know about a MK IV C.
BTW, I use a 12AX 7 from Telefunken for the first tube since some time now already, very warm and 3-D tone. My powertubes at time are 4 x 6L6-5881.

friendly regards

 

[Boogiebabies]

What a great post !!!

I am working to find out about the later MK IV versions. I have a 12/93 MK IV B and I really did not have any interest in the MK IV beyond that and the MK IV A. I can assure you that Mesa has more revisions to the MK IV above C. I have the MK IV B and a RF-C 1992 Dual Rectifier #023X and 3 IIC+'s with Simul-Class EQ and Reverb as well as a 2004 Road King. There are evolutions in every amp. The Dual Rectifier by 4/92 was already up to rev. C, the MK IV up to B and the Road King up to RK ver. 4. The IIC+'s have minor variations.

I will post back if I can find out more about the IV C,D etc.

I really think the MK IV a is an interesting unit as it has the MK IIC+ lead channel(exact circuit), MK III R2 and the MK I clean. The later versions also have modifications to the voltage of the R2 and clean channel where the amp lowers the plate voltage to the preamp tubes. The original versions did not have this, but it is a way to have a better behave R channel and a sweeter, saggier clean channel.


Ed

 

[Aart]

Thanks for all the coments, I know a lot more know.

The tech that is working on my amp is Peter van Weelden, he is really good and he has an assistent that has worked a lot with Mark IV's.

My Mark IV is being serviced now because it has been (ab)used a lot in it's 15 year career. But she will be allright now.

I like my Mark IV a lot because of it's nice high gain sound that stays tight if you're playing really fast riffs.
I owned a Peavey 5150 II(from tubefreaks bandmate) and a JCM 900 SL-X before my Mark IV, and it's the best amp I ever had.

The Marshall didn't have enough gain and wasn't tight enough and the Peavey was overkill, too brutal and too much gain, no character at all.

I'm only using the lead channel btw, sometimes clean, but mostly lead. I play melodic Hardcore punk like Pennywise most of the time.

 

[Aart]

btw, does the B or C version of the Mark IV have more gain than the A version, or is the differrence really small?

 

[Aart]

Hi Ed,

- A lot of nice info

friendly regards

Where is Wesel in germany?

I live real close to the german boarder, near Emerich(Kreis Kleve).

 

[Antoine]

How can i know which MarkIV version i have ?
mine is a short head, and on the little card attached to the amp when i have bought it (new) in 1998 there is written :
MODEL : MKIV.X 230V and just bellow : G#46
SERIAL :IV09059
Any informations ?

 

[Boogiebabies]

Does it have the satellite send? A 98 may be a B or higher version. I have not substantiated a version of C or higher. As far as gain, I would have to say the B has more gain because it does not have the 500pf cap on the plate load for the V4A. It has a few tweaks to the circuit to dull it a bit, but they are minor changes in capacitance. The MK IV A lead circuit is like a 60/100 IIC+ with the 1000pf on the V4A plate load to cut highs. The MK IV A is a bit less bright as a 500pf is used instead of the 1000pf.

 

[screengrid]

Hi Aart,

not so far away from you, approx. 50 KM ! If you drive the highway A3 in direction Düsseldorf, after around 35 - 40 KM you take the departure Wesel. Approx. 10 KM further along the B 58 you reach Wesel on the right Rhine side.

Hi Ed, you seem to be the expert here regarding Boogies. Although I also have collected a lot of prospects and schematics, you seem to know a lot of more technical informations about Mesa Boogie amps, good to know

regards

 

[Antoine]

Yes my MarkIV has the Satellite send, and just one FX loop switchable !

 

[Boogiebabies]

O.K.,


I am still working on the MK IV C info. So far even the 2005 MK IV's have the satellite send so they may have actually stopped at B.

 

[Boogiebabies]

Can one of you guys send me a bag of Lebkuchen?
My Grandmother is in Fürth, but will not send the goods.

 

[Aart]

what the hell are lebkuchen? :?:

 

[Boogiebabies]

Ginger Cookies dipped in dark chocolate. It's a Bavarian thing.


Wenn Sie deutsch waren, würden Sie wissen. Haha....