Mark IV trouble with

[maxguzzo]

hi guys!!
as 1st... happy new year!

well I was reading all the forum and it was pretty helpful to solve a trouble with my Mark IV but I still have a little bit to solve..

I had this combo, bought used some years ago...

I sold the cabinet and made it as a short head and never had trouble... anyway I tought to sell it and gave it to my drummer that is into playin guitar too...
he had it for some months but of course it was pretty difficult to use it for him, so after some month without having been used, I got it back.

actually, I sold my rectifier rectoverb and decided to use again the Mark IV (I still got a fantastic F30 too)

the matter is that the after lots of months without having been used, I had that trouble:

all the volume was almost low in every channel, mostly in rythm 1 and 2.
in lead channel looks like everything was workin fine even if volume was goin a little bit up and down,
in rythm 1 and 2 the sound was damn crazy too, very disturbed and noisy, like when u have to turn the pot to get signal clean again

after reading here I decided to clean every pot with a spray for contacts of course, I did it the same on the
send return... right now, looks like things are ok when I use it in full mode, but still have some trouble, the same
trouble described above, when using the tweed mode...

so I m some confused, how should I procede?!

i tried to change valve, all the final valve but nothing happened..
and if i m not wrong all the pre valve has been changes very recently...

I tought to change all the pre valve and try with those of the F30 that are perfectly working, but they are only 4
and the Mark IV has the 5th about phase if I m not wrong so..

any suggestion please?

U think that it may be just a valve trouble or something more important? a better cleaning inside maybe?
tought that it could be a trouble on cleaning some contact on the selector FULL/TWEED, may it be?!

thanks everybody for help!!!

and sorry for my english! it will maybe be full of mistakes but I think u understand it anyway

and...this is a f**** board... a really f***** cool board!! ))

ciao and special thx!!!!!

Max

 

[Platypus]

Max, that sounds like a preamp tube issue to me.

Check V2 and replace it with a known good 12AX7. The first triode handles the rhythm mode gain stages and the fifth lead gain so that would explain the volume fluctuations on the lead mode too, and the second triode handles the FX return.

I am willing to bet if you replace V2 or V1 your problems would go away.

A very quick and dirty test would be to turn the amp on and lightly tape each preamp tube with the eraser end of a pencil.. they will make some noise but your bad tube will make a LOT of noise.

 

[maxguzzo]

Max, that sounds like a preamp tube issue to me.

Check V2 and replace it with a known good 12AX7. The first triode handles the rhythm mode gain stages and the fifth lead gain so that would explain the volume fluctuations on the lead mode too, and the second triode handles the FX return.

I am willing to bet if you replace V2 or V1 your problems would go away.

A very quick and dirty test would be to turn the amp on and lightly tape each preamp tube with the eraser end of a pencil.. they will make some noise but your bad tube will make a LOT of noise.

oh thx so much!
I m gonna give a try!
I also realized right now that on V5 there is written 12AT7 by someone else test I supose (or directly from Mesa? dunno)
but they were replaced with 5 12AX7.
May this be the trouble also?

thx so much for your feedback!

 

[maxguzzo]

WOW!
I think I solved it all!!

I just cleaned all the contact, also into the valve connector, and YEAH!!! looks like is workin fine now!!!
can't wait to see in the next days if it will keep workin fine!

thx everybody!!




HAPPY 2010!