Problem with Mark IV

[jimmybcool]

Hi all,

Well, I bought a used Mark IV for my first real amp and so far I love it. But I have one problem, maybe.

When I first power up I always start it on standby and wait about 1 minute. Then go to power on.

And this worksfor the 2 rhythm channels. They fire right up and are clen and crisp. But the lead channel is sometimes muted and underpowered. Eventually it warms up and everything is OK.

Should I be concerned with this or just accept that tube tech is what it is.

 

[NoGlassNoClass]

Sounds like you may be losing a preamp tube. Since the amp is used, you dont really know how old the tubes are or how hard the amp has been run. Think I would change them all, and keep the old ones as spares.

 

[jimmybcool]

OK. Thanks. Not sure what a preamp tube is but I'll look into it and replace them all. Can't cost that much.

I like learning stuff anyway. 8)

 

[jimmybcool]

OK. I just "sperymented" with my amp.

First, I found a tube taped into a spare tube holder on the side of the enclosure. It is/was a Mesa 12AX7-A. It has two pins that are bent. I will toss this as I don't belive in trying to correct bent pins to this extreme. Why the previous owner kept it I don't know.

Now, from what I can tell, the power-amp tubes are the four 6V6s. I also have two EL34 in boxes and I just tried them in the two outside positions. Yup, it got a bit creamier and raspier. The warm up issue is still there.

I am "assuming" since there is no diagram and i don''t want to remove them all until I get the replacements that the preamp tubes are all 12AX7-As. I will call Mesa Monday AM and make confirm and order them.

I think I shall also order 2 6V6s as replacement/spares since they don't cost much.

And I think I'll run her in the standard 4x6V6 tube mode as overall I like the range of tones better.

But it is nice to know the option for the EL34s is there.

 

[wrxmania]

Remember there are specific modes you need to run 6V6's in compared to the other valves in the amp.

Try Bob at http://www.eurotubes.com for great advice and maybe some better tubes at a better price than the Mesa ones - unless your amp is still under warranty?

Remember to buy a spare 12AX7/ECC83 valve for the space of the bent one - you may need it one day!

Brian

 

[jimmybcool]

Oops. I meant 6L6s. I don't want to change to the 6V6s.

I just want to replace all the tubes with new to assure continued good tone.

I'll check out eurotubes. Thanks

 

[zeppman]

I believe the 12ax7-a is just mesas version of a lower noise, higher gain pre-amp tube, usually for V1. I would do a complete retube from eurotubes if I were you. Great tone and much cheaper than mesa tubes. You can do a full re-tube for around $100. Bob knows what he is doing with his tubes, along with doug at dougstubes.com, and tubedepot.com.

 

[jimmybcool]

Tubes are in the mail 8)

Hope to have them by the weekend. Thanks

 

[wrxmania]

Mesa?

Eurotubes?

 

[jimmybcool]

Eurotubes.

8)

 

[vulture2600]

eurotubes!!!

 

[jimmybcool]

Jeez, is Eurotubes down the street or what? I though I ordered these on Tuesday. I know it was Monday the earliest.

Just got them. Now I gotta go plug them in and give it a spin.

I'll be back. 8)

 

[zeppman]

Great, let us know what kind of power tube config you got, and what you think of them.

 

[jimmybcool]

OK. What I got was:

Mesa MK IV Standard retube with 6L6GC's
PRICE: 101.00
DESC: A quad of JJ 6L6GC's for a deep fat sound along with 5 JJ ECC83S's with one balanced for the phase inverter in V5. Very fat, full & smooth.

So far I am still experimenting. First impression is these are a lot LOUDER than the Mesa tubes. I practice in a small room and the individual output levels and the output master were all set around 3 before and are now at 1.5. And I had to turn donw the volume on the guitar.

I need to spend some real time experimenting on how to get the tones I want in the volume range I like. One thing I love about this Mesa is the endless possibilities. One thing I hate is the endless possibilities. With these new tubes I need to do some tweaking to get the right sound.

I can say that the clean is CLEAN and rich. I'm just having trouble with the lead channel getting the right mix.

I'll be back with more when I find the right settings.

 

[RR]

Try cleaning the tube sockets with "Blue Shower" comes in an aresol can you find at your electronic shop. You can also use something that is similar at Radio Shack. Not sure what's its called. It comes in an aresol can to clean circuits or TV channel tuner.
What :shock: rotary TV channel changer? What is that?

 

[jimmybcool]

RR

Can you explain what I would be using the Blue Shower for? I don't understand the suggestion.

Thanks