red plating on one of the el34's on my mark IV

[JimAnsell]

so i got my mark IV today and i've been tweeking for well over an hour now.
all the sudden i noticed it humming really loud, even with my noise gate.
then i look in the back on one of the el34's is red plating like a mofo :shock:
so i shut it off, unplug it, open it up, etc.
nothing is damaged on the inside. the tube sounds like there is something shaking in it.
i put them back in and turned it on carefully on tweed power and then to full power and let it go for a while just watching the tube.
everything seemed fine, so i started jamming again for a while.
it was sounding great, then it did it again.

so am i safe to assume its just the tube?
i don't have any el34's around to test it.
i measured the screen grid resistors when i was had it apart and they were all fine.

 

[disassembled]

As long as the screens survived you should be ok. The schematic is on tubefreak.com so you can make sure it has the right values inside.



Greg

 

[Platypus]

Probably just a bad tube, get a new matched duet. The shaking inside the tube does not neccesarily mean something is loose inside, most likely loose spacers rattling/hitting the glass.

 

[JimAnsell]

it ended up being the tubes.

man, this amp is amazing.
i've owned 3 of these before and always sold them, but not this one.
i think its because i used to play them through marshall cabs.
now i'm using a boogie 2x12.
sounds killer at all volumes.

 

[Platypus]

it ended up being the tubes.

man, this amp is amazing.
i've owned 3 of these before and always sold them, but not this one.
i think its because i used to play them through marshall cabs.
now i'm using a boogie 2x12.
sounds killer at all volumes.

It sure does, love my boogie 2x12 w/ mark IV.

Tone heaven.

 

[disassembled]

Man i can't play mine until July! Oh well I am happy with the TA and 290 so it's all good.

Greg

 

[JimAnsell]

how deep is the reverb supposed to be on this amp?
mine seems kinda weak.
when the reverb is dimed, its about the equivilant to the reverb being on 4 on my fender pro reverb.
the tubes all tested fine too.
maybe the tank is going?

 

[Russ]

The reverb isn't real strong in the amp. It actually isn't the greatest reverb either. If you want real reverb you will need to get some outboard reverb and put it in your loop.

 

[JimAnsell]

The reverb isn't real strong in the amp. It actually isn't the greatest reverb either. If you want real reverb you will need to get some outboard reverb and put it in your loop.

is that why they didn't put a reverb switch on the mark IV footswitch? :lol:

 

[Russ]

I think you can use a single tip to ground 1/4" type switch into the jack in the back if so equipped. If not you have to do the little mod Boogiebabies talked about on here that uses RCAs and creates a switchable reverb.

 

[JOEY B.]

Try replacing the reverb unit with an Accutronics model #9AB3A1B. This will replace your factory unit and will have more reverb decay. Do a search on Ebay, they have a store there.

 

[eltrain858]

what kind of music do you play? i can't stand turning my reverb up past 4 or 5