Mark IV Reverb Question

[bocage44]

Hello All,

I recently purchased a Mark IV head and 2 Theile cabs from eBay. So far I'm really impressed with the amp; however, the reverb does not appear to be working at all - is this likely a tube issue?

Also, at moderate-to-high volume levels I'm getting radio broadcasts through the amp. What can I do to stop this?

 

[zeppman]

Hey bocage, congrats on the ebay win! Each pre-amp tube runs in a way that half the tube does one function while the other half does another. I believe the reverb send and return are split amongst two different tubes, so in order for the reverb to not be working something else would also not be sounding right. Either that our you could actually have two bad pre-amp tubes. My guess is that the reverb tank is not connected to the amp. My amp is a combo, but if it is the same setup besides the speaker, there should be two rca type looking plugs that come from the reverb tank and plug into the top of the amp housing and to the left of the speaker. Check that out first. Then try tubes or possibly even a new cap job. What year is the mark? Also, for what its worth, my mark iv's reverb is not the strongest. Don't expect anything fender like. I actually went out and bought a EH Holy Grail because i was not happy with the minimal amount of reverb from the actual amp.

As far as the radio stations, i get that too, but i also play a strat. I just deal with it; it only happens everyonce in a while. If you have single coil pups, try shielding them and you guitar body cavity.

 

[Rich M]

If tank is connected, it may be that the springs inside became unhooked during shipping. Might check that out as well. I would check tubes also. If either send or return tube is cooked, reverb won't work. I've had plenty of tubes fail, esp. current production garbage. You can have just one half fail.

 

[bocage44]

Thanks for the responses guys!

I don't think the springs are disconnected in the tank - when I move the head around I can hear that distinctive "klaaaanggg" that accompanies such an act when the amp is on.

Based upon what I've read in owner's manual, I figured that if one of the tubes assigned to the reverb function went bad, I'd hear it in some other element of the amp's operation. At any rate, I'm going to check each tube this afternoon and see what shakes out....

Hey zeppman, I'm not really sure what year this amp is - how does one find this out? Also, thanks for the comments regarding the shielding. I was playing my '58 Les Paul reissue last night, so I don't think that would be an issue. Plus, the radio transmissions came through the amp even when I wasn't plugged in....

 

[t0aj15]

About the radio reception, I had a bad problem with my Mark IV recieving the one million watt moldie-oldie station signal that is broadcast less then two blocks from my house. After going through every cable, pedal. connector, etc., that I own I was finally able to eliminate it by using a Furman Power Factor Pro power conditioner. It costs a couple hundred $'s but IMO was well worth the money. It comes in two forms, see them here:
http://www.furmansound.com/products/pro/pwr_cond_seq/cond/pfpro.php

 

[Boogiebabies]

My 58 RI shreaks like a mofo through all of my MK series amps. The pickups are not potted and severly microphonic. I have to use a Boss NS-1 and even then it is a hassle. Every once in a while I will pick up radio free europe or some German schnitzel, but it is only when the guitar and cord are connected. It's like the beginning of Surfing with the alien. A monster cable was a big improvement to prevent this as well. Also make sure you did not use a speaker cable to plug your guitar in. After 23 years of playing I mistakingly grabbed a speaker cable and plugged my guitar and amp up. It was a radio fury and squealed like a pig.

 

[Boogiebabies]

It is funny how Mesa's reverb differs vastly. I have a MK IV with a ton of reverb and two IIC+'s with a tone. Yet, one IIC+ is weak as could be and all the components are in spec.

 

[Rich M]

I don't think the springs are disconnected in the tank - when I move the head around I can hear that distinctive "klaaaanggg" that accompanies such an act when the amp is on.

Try the tubes. If that doesn't work, I'd still check the tank. The clang may be the subassembly, which floats on short stubby springs, banging around.

 

[mangley]

Probably the reverb driver tube.

BTW - I have a plug in my reverb switch jack disabling it. Personally I think the reverb is the weakest link in an otherwise great amp. I use a bit of delay from a TC M-One in the loop with a rane mixer. Sounds great.

 

[RussB]

Hearing the reverb "crash" tells me that the reverb return is functioning. I suspect a broken wire in the reverb itself, or a bad cable connection going INTO the reverb tank.

Reverb replacement tanks are cheap

Look up part # P-R8AB2A1B here, http://www.tubesandmore.com/

 

[bocage44]

Thanks again for the great responses!

Well, I replaced all of the tubes with a set of JJ's from Eurotubes - no difference (in the reverb response anyway). I then removed the reverb tank and checked the springs as suggested - everything was good there. Made sure the connections were all secure - still no reverb. At this point I'm guessing either the reverb is simply underwhelming in this particular amp, or the tank needs to be replaced.

At any rate, I ran an old Boss DM 2 throught the effects loop this morning - I don't think I'll be missing the reverb too much!

The reverb issue aside, I'm really enjoying this amp! It's everything I'd hoped it would be!!!!

 

[Rich M]

I misunderstood about the clang when the amp is ON. Agree your problem has to be upstream from the springs. The reverb on a mark IV is NOT underwhelming. Might be a job for someone with a scope. I just got one a couple weeks ago - pretty cool sounding.