help diagnosing T-Verb cut out problem

[mbmesa]

Hi , I am asking for your experienced help in diagnosing my T-verb issue. It all started about six months ago when during a jam the sound started farting out and losing power big time. It cut in and out and eventually cut out to a very low volume. At all times I could hear sound but very, very low. So I turned it off and brought it home from the jam.

The next day I turned it on to diagnose it and it was fine. It was fine for about a month and the problem happened again. Brought it home and the next day it was fine again. Very hard to diagnose.

So I figured I'd start chaning out the tubes a few at a time and see if the problem goes away. In otherwords, I was hoping it would not cut out anymore randomly. I changed the power tubes and V1. The problem would still happen about once a month.

Well last jam it died again and now it stayed that way even at home. Good . now with your help I can hopefully diagnose and fix it. The amp is not totally dead. I can still hear the sound and the dirt channel is dirty and the clean channel is clean. The volume is very very low however. The volume controls have an effect but the total loudness is very low.

I swapped each preamp tube , one by one with new tubes and it does not
help. now I have totally new tubes for both power and pre-amp.

One thing I noticed on the dirt channel is if I turn the volume up really loud (but its not loud) then The amp will develop a hum. If I turn down the gain and volume the hum will go away. At all times I can hear sound but very very low.

I would appreciate any tips you may have. Thanks.

 

[Charlie]

Did you try changing out your rectifier tubes?

 

[mbmesa]

That thought did occur to me but to rule that out, I switched it to the solid state rectifier instead of the tubes and have been using that setting for all my tests so far. Are the tubes somehow still in the circuit even if I'm using the silicon diodes setting ?

 

[Platypus]

Yes, the tubes are still 'in the circuit' even though you're in diode mode. I had a bad rectifier tube and my problem persisted despite me using the diode rectifiers.

However, the issues mine exhibited were much different than yours.. yours really does sound like a classic preamp tube issue. You switched them all out so that makes things a bit more interesting. Are you 100% sure the tubes you replaced your preamp section with were all working tubes?

Other things to consider.. have you tried another guitar with it? Different guitar cables? These could be part of the equation too even though they are simple to overlook. Bad guitar cables can cause volume dropping/farting out as well.

Is it possible one of the control pots has come loose? Do any of them wiggle?

 

[jbird]

F/X Loop jacks dirty?

 

[mbmesa]

I just finished some more experimentation and am waiting for the tubes to cool down before my next experiment so I thought i'd update you.

The tubes were all new from Doug's tubes so I know they have been tested and shipped properly but I guess I can;t rule anything out. The guitar throgh the same cable into another amp sounds fine. I did these tests:

I tried the slave out into another amp and was able to get good levels out of it. i.e. the output level equalled about a guitar level output. My guitar straight into the other amp or the slave out of the T-Verb into the other amp yielded about the same output level coming out of the other amp.

I then tried my guitar straight into a pedal and then straight into the power amp through the FX return. This yielded a low level similar to what I am getting using the amp normally (with guitar going in the front). So it seems the problem could be in the power section but its not conclusive yet. NExt I will try my pod into the power amp in.

I then tried pulling out 2 power tubes and one rectifier tube and moving the speaker jack to 4 ohms. This yielded slightly more volume but nowhere near where it should be. Next I will try moving the rectifier tube to the other socket and then the same tests using the other rectifier tube to see what happens.

Any other suggestions based on the above ?

 

[mbmesa]

Well I have had a break through of sorts. I tried swapping out and moving rectifier tubes from (rectifier) socket to other (rectifier) socket and swapping rectifier tubes and it had no change. (I am in 50 watt mode -- two power tubes/one rectifier)

Then for fun I tried BOLD instead of SPONGY and WHAM my power came back and the amp was loud again. I then switched it back to SPONGY and the power was still there but as I was playing slowly started to fade and the notes started farting out and getting what sounds like intermodulation distortion. I was on the clean channel and as the power was slowly fading the notes would have a layer of fuzz on them (on the clean channel) that varied with how hard I picked. It took a couple of minutes and the power/volume became low again.

I switched it back to BOLD and the power/volume came back again and the fuzz and farting out dissapeared. I tried going back and forth and it seems my problem only happens on the spongy setting. The notes star t to fart out and the volume dissapears and the amp becomes low volume. It takes about 1 or 2 minutes to reach the low volume level after going from bold to spongy.

Anybody see something like tha before ? What do you suggest ?

 

[Charlie]

Sounds like it's time to take it to a tech.

:?

 

[Charlie]

Sounds like it's time to take it to a tech.

:?

On second thought... how much volume are you losing in Spongy mode? My Stiletto loses a LOT of volume in spongy mode. So unless my amp is also broken then maybe this is just normal operation?

I'd like to know. I've never played another boogie with the spongy option so I'd like to know if there is something wrong with my amp. I've always assumed less power=less volume.

 

[Charlie]

Update:

Did a little searching on the forum and found this:

'Update: After the tube change, I had an issue with the Spongy power mode dropping down very low in volume. The Mesa rep had me do a test bypassing the loop in clean mode to see if it still does it (it didn't) and then do it in the second channel (the volume dropped) Before mentioning that I had changed the preamp tubes, Mesa told me some tubes in V3 and V4 "sponge out too much". I then told him that I had changed all of the preamp tubes except V4, the loop, and that I would put the stock Mesa tube back in V3 and try it. well, now it works normal again.

Long story short - Keep the stock Mesa tubes in V3 and V4. You'll save yourself some money that way and be able to put the $15 Tung-Sols in V1, V2 and V3 which by the way sound fantastic.'

This is quoted from this thread:

http://forum.grailtone.com/viewtopic.php?t=10122&start=0

 

[mbmesa]

Thanks charlie. I lose a LOT of volume and the sound eventually starts getting distorted like a torn speaker . The notes have a buzz/fuzz layer on top of the clean sound. The master and the channel volume at noon (half way) produce just enough sound to practice at 10 pm in my basement without annoying anybody , to give you an idea.

This started happening with the stock tubes. I then started replacing them one by one until all were replaced. I will try going back to stock one by one and see what happens.

 

[Charlie]

Well with my Stiletto set up as follows:

100 watt setting, spongy, tube rectifier, clean channel, loop bypassed Preamp at about 10/11 o'clock and the master at 12 oclock the amp really is not loud at all - pretty much bedroom playing volume.

The amp sounds fine though... just low volume.

Can somebody let me know if this is normal? This is the only amp with a spongy option I've ever played so I have no point of reference to know if things are operating properly.

 

[Charlie]

Well I fixed my low volume problem I hope this info helps you solve yours:

So here are the tubes I was running in my Stiletto before:

P1-Tung Sol P2-Tung Sol P3-Tung Sol P4-Mesa Boogie 12ax7 P5-Mesa Boogie 12ax7

I replaced the P3 with a Ruby Tubes ECC83 (12ax7) I had laying around and then took the Tung Sol from P3 and plugged it into P4(the tube used for the fx loop).

Lo and Behold! The amp is loud as f!@# now - only problem was when I tried engaging the fx loop the amp sounded terrible (the loop sounded fine before) and got a bad type of distortion - a broken speaker type of sound. So I took out the P4 Tung Sol and replaced it with a stock Boogie 12ax7 and now everything works great.

So I either had a bum Tung Sol 12ax7 or maybe these tubes just don't work well in these positions in a Boogie.

So it looks like my amp was running off of one testicle I can't wait to get it in a practice room and crank it up.

Hope this info helps.... good luck!

:wink:

 

[mbmesa]

Wow ! I have brand new Tung-Sol tubes in V1 V2 and V3 . I will have do more swapping and testing ! Thanks charlie.

 

[Charlie]

Cool - well let me know how it turns out I'm interested to find out if it's the same problem.

 

[Boogiebabies]

Does anyone think it's the switch ?

 

[mbmesa]

The problem seems to be solved ! Based on Charlie's experiences, I took out the brand new Tung-Sol from V3 and put it my old MB 12AX7 that used to be in V1 before I bought new tubes and BAM ! LOUD and CLEAR !. Now it remains to be seen if it will stay that way.

So to summarize and to possibly help someone else with a similar volume and cut out issue when in Spongy mode, here is what happened in my case:

Initially I started getting the intermittent low volume and cutting out problem on spongy mode (but I didn't know at the time it was only in spongy mode at the time) and it was intermittent. I bought brand new tubes (3 Tung Sols, some JJ, some Penta Labs Chinese). I changed the tubes one by one. Put in a Tung-Sol in V1, intermittent problem still there. Put another Tung-sol in V2, problem still there. Put another Tung-Sol in V3, problem still there. After each tube change I had a full 3 hour jam and it would start cutting out after about an hour or two and would be fine when I brought it home . Few jams later, it cut out and stayed out. Really low volume and staticky output. I tried many things as detailed above.

I spoke to Mesa about it and they said some pre-amp tubes are involved in managing the spongy circuit and that Mesa Tubes should be used in those as not all tubes work reliably there. Based on that and also what Charlie said, I put it an old Mesa tube that was previously in V1 and it started working again.

So my unfortunate string of events was that I had a Mesa 12AX7 die on me in V3, and I replaced with a new Tung-Sol that does not work in V3. I thought the problem was not the tubes at that time because the problem stayed after each new tube. So when Charlie said he had a Tung-sol in there and also had low volume issue , it clicked.

The moral of the story is that some or all Tung-Sols (myself and charlie had the issue) will give you low volume issues in V3 and possibly V4. They may be fine in other positions and in other amps (I tested them) but not in V3 and V4.

I'll update you if the problem comes back intermittently or otherwise. For me, I am going back to Mesa 12AX7s in V3 and V4 (at least) from now on.

 

[Charlie]

Cool man!

Sounds like that fixed it and I hope it continues to work properly. Well that looks like 3 people with volume problems while using the Tung Sols in V3. Interesting... but at least we'll have this information available if this happens to anybody else.