Mark IV newbie tube replacement question.

[spikemauler]

Hi,
I have a Mark IV short head.I ordered pre-amp and power tubes to replace the existing ones.I've never changed pre-amp tubes before and was wondering how to do this.Do I just remove the power tubes then try pull out the pre-amps?It looks pretty tight back there.Will my hands fit?Or do you have to take something apart to replace the pre-amps?Also, one of the pre-amp tubes is sheilded.How do you remove the sheild?
Thanks, and sorry for the seemingly stupid questions.

 

[Brewski]

Hey there. The pre amp tubes will be easier to access, if you pull the power tubes. When you say "remove the shield" are you speaking of the aluminum cans that protect the pre amp tubes? If so, they have springs that press against the top of the tubes. Just turn them about a quarter turn or so, and they should pop off. You'll see where there are slots that line up to hold them in place, when you're putting them back on. Just line up the slots with the holes, press and turn, to put them back on.

Just replace your pre amp tubes like you would your power tubes. Wiggle them slightly and pull them out. When you are putting the new ones in, just make sure that the pins are lined up and take care that you don't bend the pins.

As far as your hands fitting, they should. On my F-50 and RK, there is a metal bar on the back of the amp that I take off, as well, which gives me more access. I'm not sure if your amp has that too.

You may need to use a small mirror to confirm the connector direction, which will help you line up the pins.

I hope that helps.

 

[cesjr]

If I'm not mistaken your front grille should be able to come off. I have a mark IV medium head and the front grille is attached with velcro and can be easily removed to access the preamp tubes.

Hope this helps,

CJ

 

[spikemauler]

If I'm not mistaken your front grille should be able to come off. I have a mark IV medium head and the front grille is attached with velcro and can be easily removed to access the preamp tubes.

Hope this helps,

CJ

Wow,I just went downstairs and pulled that grille right off!F***ing velcro!I would have never thought of doing that.Why dont they mention that in the owners manual?Anyway,the pre-amp tubes are right there,very easily accessed now.Thanks CJ! And thanks Brewski for the "Can" info.

 

[Russ]

That velcro thing must be a modern convenience. My a head forces you to try to access from the rear. It gets pretty tight for guys with big hands like myself. Kind of like... well let's not go there :wink:

In order to do anything remotely close to the front of the chassis is hard to get to. I just installed a new reverb tank. To get the RCA plugs in was by braille. I know I could have just left the chassis out to connect them but I had already gotten it back in. Those of you who have dropped your chassis out know what a pain it can be to get the thing perfect again. I had to take the chassis out to get the reverb tank in because the screws toward the front of the case were inaccessible without it removed.

So you guys with the b version, what is the fan mounted to if the front is open so you can access the preamp tubes? Is it mounted to the bottom?

In the a it mounts to the front panel behind the front panel and you push it through the slot and use angle brackets like the I, II, and III.

I just got a b head case so I am going to migrate into it as soon as I go pick it up. The front access is going to be nice. Thanks for the info about the velcro...

 

[spikemauler]

Russ, mine(MarkIV fan)is mounted to the bottom.

 

[Russ]

Thanks spike.

I needed to know so when i swap cases I will have a clue before I get creative.

 

[cesjr]

No problem spikemauler, glad I could help. I couldn't imagine getting to the preamp tubes without removing the front grille.

 

[SeasonOfPain]

Hm, I just tried this on my 2005 Mark IV wide combo and couldn't find any velcro attachments. I had to access from the rear. Maybe the velcro thing is only on the heads?

As for tube changing, I just did my first retube ever on the Mark IV with a new set of high-gain JJ's from Eurotubes. It wasn't actually that bad once I removed the power tubes (I was replacing them anyway). The shield around the V1 was actually the hardest thing to figure out how to remove... I was worried that I wasn't doing it right, but got it off eventually. I had to tug on it fairly hard to get it off after twisting it and lining the "studs" up with the "shafts" on the sides of the shield. It was also a bit tricky lining up the pins on the V3 socket (I can't easily see the socket from the back). Went okay, though, and I like the sound so far. Much quieter than the stock Mesa tubes (power tubes were about a year old and questionable).

One thing I that threw me was the double-number "ratings" hand-written on the tube boxes: I'm not sure what the numbers actually are a measurement of. I put them in sort of "ascending" order from V1 to V4:

V4: 110 113
V3: 110 114
V2: 111 115
V1: 115 113

Hopefully I did this "right". I'd assume any combo would work in V1-V4, but I was looking for the optimum combo for a liquid high-gain, Petrucci-esque sound. From what I read in the manual the V1 affects the tone much more than the V4. For a high-gain set, I'd want the higher numbers in the V1, right?

 

[Shep]

wat are the best high gain preamp tube for mk iv's?

 

[Russ]

Season, you might have to remove the remove the grille by the screws. This isn't a guarantee by any means that you will gain better access because the baffle might still be in the way. I think it is a good idea to have the front access on the head because it is really tight in there. You can always turn your combo upside down if you need to stick your head in there.

 

[Russ]

Your order looks good as far as tube values go. The best tube wants to be in V1 because it sets the stage for your amp. The lower figure tubes can follow and descend because it is the circuit controlling them anyway and your gain is cascading across them as you got all the way to lead. Good call.

 

[Russ]

The 2 values per tube are relating to the strength of the tube per side. A 12ax7 is a dual triode. Each side has its own value thus the 2 readings and subsequent ratings/markings on your boxes. The higher it is the more gain it will have. Yours are rated above expected standard new. The standard new score would be theoretically 100/100. Nice tubes...

 

[SeasonOfPain]

Sweet, thanks Russ for the excellent replies-- exactly what I needed to know.

Shep, I can now by personal experience give JJ's (from Bob's Eurotubes) an enthusiastic "thumbs up".