Does your amp get louder as the night goes on???

[McBarry]

As the bias drifts, it allows the 6L6's to conduct more or mess (seems more in this case).

Seeing as we're taking pot-shots from the sidelines (or half way round the world in my case...LOL) my initial instinct was a coupling cap starting poor but improving with heat - and this is quite a longshot in my mind.
Along the same line, an LDR could have same effect, but I'd rather suspect the amp to be at full working temp long before first set had finished, and hence symptoms to appear half way through first set, or so.

If we're thinking thermal anomalies lets not forget the simple FX loop jacks also, aka MkII/MkIII common fault. Actually, only last week I had major dropped sound levels from my MkIIB simul - had me stumped until I nudged the FX return jack - BOOM, full level restored. Quick clean, returned the cutout arm to position and away we go. Worth a though..

Still keen to hear what it actually ends up being..
Dave

 

[Monsta-Tone]

It's entirely possible that the bias is drifting when the amp gets hot.
The relay, EQ, and bias supply are all fed from the same transformer tap.

My hopes are that the relay supply resistors were causing the bias to drift.
I did not look at the tubes last time to see if they were red plating. I don't think they were because I have O-Rings around the power tubes and they are just slightly discolored, not burned.

The Return jack was just cleaned a few weeks ago. They tend to get dirty in the rain forest and I have to clean them regularly. The Send jack was replaced at that time. Maybe I should just replace the return as well. It's the original one.
The loop is always in use, so it might be a good idea.


I thought it was a filter cap at 1st too, but that usually causes the amp to sound weaker and weaker. Mine starts out sounding exactly as it should.
I turn it on about an hour before practice and just leave it in standby so that it warms up a bit.

I don't think it's the power transformer. I just installed a full set of Mercury Magnetics in the amp. It had the volume increase problem before I did this. I was originally thinking that it was the output transformer getting hotter and making the amp louder or that the power transformer was drifting as it got hotter.
I think the new power transformer has more available current so now the problem is really manifesting itself.

Hopefully I found it. If not, I'll just replace the entire low volt supply. I have everything in stock and it would only take an hour or so.

 

[McBarry]

Monsta, not sure how much bias change is needed to change volume - Mike B would be yr man I reckon, or you could experiment with a trim pot...
New trannies absolves them, in my mind.
Re cap(s), coupling, NOT filter. But it'd be a bizzare symptom ie: cap starts weak and improves conduction after it heats.
I guess if there's cathode bypass caps, one of them could be the culprit. Long shot, but we seem to be in grey water here...
Given the thermal nature of it, have you considered a dry joint?? I know it's a ******* thing to suggest as it's a subtle fault, but it'd be high on my suspect list.
Some ideas:
Chopstick the hell outta it, but gently and mainly when cold. Unless U want to cold-spray it in specific areas.
Measure the bias voltage both stone cold, med warm and when volume increases.
Measure the signal AC (yep, use a siggen as sduck mentioned) at V1, V2, PI input and PI output. Again when cold, med warm and when vol increases.
Maybe if Ed reads this he might have some experienced and sage suggestions..
Good luck..
Sounds like some serious operating-theatre time is gonna be booked. Hope the surgeon has a short list that day...LOL :wink: :lol: :lol:
Dave
PS: U still away, or moved back to mainland now?? Just curious.. DB

 

[Monsta-Tone]

Thanks Dave,
I re-soldered all power amp connections last night when I was inside the amp.
I didn't see any that were suspect though.

I might have to order some caps from Mesa. I used the last ones in a customer's amp months ago.

I might check the cathode caps. Didn't think of that. I didn't check to see if it happens in both channels either.
Basically, we were on our last song and it didn't have any clean parts, so it didn't occur to me.

I'm going to fire it up next to a wall, where it will get really hot and leave it on for a few hours tonight just to see. Hopefully, the LV power supply resistors fixed it!

 

[McBarry]

Andy just remember the bias should theoretically only change the "tone", ie; headroom, distortion and I reckon if it's changing the volume that dramatically, then something is seriously amiss in the 6L6's operation.
U could also take a line out from the FX loop or similar and when symptoms occur an anomaly here will direct U to the preamp.
Even a dual-trace CRO would be great as you'd visually see a jump in AC amplitude in a heartbeat.. esp if one was on post-power amp and one post preamp.

Not being a betting man, (for good reason...LOL), but my money is on pre-amp somewhere..
Just puttin' it out there..LOL
DB

 

[Monsta-Tone]

Not being a betting man,

:lol: No worries mate! That's why I put it out there. I've never seen this before.

I have noticed that the hotter you bias the amp, the louder it will get (within reason).
I'm thinking that since the LV power supply is tied to the EQ and bais supplies, that it was causing all 3 of them to drift when the resistors got hot.
The EQ can change the volume dramatically.
The bias can change the clarity dramatically.
The switching supply can do all sorts of odd things.
Maybe it was just a strange combination of all of them. All of my engineering classes were over 20 years ago and I didn't use them for the 1st 10 years after so I have probably forgotten more than most people.

I did turn the amp to 2 and place it against a wall for a few hours this evening after replacing the resistors.
No problems so far, but I didn't play it the whole time. I played it for about 30 minutes and then left it on while I was re-wiring my pedal board.

I'll know tomorrow at band practice.

 

[Monsta-Tone]

Well......
The good news is, the volume was fairly steady. It got a little louder after about 1/2 hour, but after I turned it down the 1st time, it stayed steady.

The bad news is, it only took an hour at medium volume to turn into mud sound.
I ordered a quad of 6L6's and new PI tube right after practice. Hopefully they will arrive before next Saturday.

First it was the dirty channel that sounded crappy, then the cleans lost a lot of headroom and had no highs.
Nature of the beast I guess!

I'll report back after the tube swap.

 

[Rob Lockwood]

Its odd that the amp gets muddy even when its getting louder because a muddy sound needs a lot more power to cut through the band than a clear one so a muddy sound is usually heard as quieter. Mud sound may mean less treble frequencies getting through, but again less treble usually = quieter, so as it gets louder that suggests more bass & low mids as the amp warms up. I think its normal for tube amps to sound warmer as the components warm up, but I dont think it should be it shouldn't be a complete change in sound.

Worn tubes do cause mud sound of course, but also usually less output, but its usually the first place to start. If not I wonder if a signal capacitor could be failing with heat as a couple of others have mentioned, if the capacitance of a coupling capacitor drops, more low frequency sound can get through. Just an idea, hope the tubes sort it out!

 

[Tommy_G]

Sometimes alcohol can make an amp get louder too.

I thought they just got better looking?
.....

I do turn my amp up as the night goes on, maybe to compensate for the band playing louder or ear fatigue, or whatever.

However, I find that my Mesa's start sounding a lot more dynamic and swirly after about an hour. The tone is better, not worse.

Its gotta be some drift caused by component temperatures that are bringing the amp closer to the bias sweet spot under the operating conditions of the amp.

If the tone is getting muddier, that's probably because the drift is taking it out of the bias sweet spot.

I use Yellows and Green rated Mesa tubes. What are you guys who are having the problems using?

 

[Monsta-Tone]

Sometimes alcohol can make an amp get louder too.

I thought they just got better looking?

:lol: :lol: There isn't enough alcohol on this island to make the girls at our gig yesterday look better! :lol: :lol:

 

[gts]

Don't all guitarists amps get louder as the night goes on (regardless of make and model)?

 

[Monsta-Tone]

Mine is automatic! Maybe I should find a way to market it.
"This amp will automatically be louder that your other guitarist! You won't even have to touch a knob....." :lol:

 

[McBarry]

Any news Andy - I'm interested to hear the outcome.. DB :wink:

 

[Monsta-Tone]

Well....I feel like a big dummy!
I could never get the amp to get louder on it's own. It was such a sporadic thing, and it only happened after playing for quite a while.
I tried leaving the amp on for hours and then coming back to it, but that didn't work.

I had been using a Rocktron Patchmate Floor to control my amp and the pedal board.
It is supposed to have relays for the switching. In fact, you can hear the switch on certain presets.
I think that the relay in the Patchmate for the amp's Graphic EQ is switching but the LED is not turning on.

We had an outdoor gig last weekend.
The amp did great up until our last set. Then I started to notice that it was sounding mushy and LOUD.

What I found was that when I push the Store button on the Patchmate, the sound gets mushy.
You basically push the Store button to put the PM into Preset Select Mode.
So....I primarily use this on the clean parts. I switch to a clean preset, then, I push the Store button so that all I have to do is hit 1 button to go back into the heavy part.
This works very well for the 1st hour or 2, then it just gets weird.

I noticed this at 1st (at the gig) because I could hear the Chorus on the clean channel when the preset was clean amp channel with no FX.
I thought it was just the acoustics of the concrete pavillion that we were playing in.
Then, the amp started getting loud again, but when we would start a new song, everything would work again.
I think this is due to the fact that I always hit the channel select button on the PM at the end of the song so that there is no amp hiss, especially if there is a delay on the fade out.

I thought it was the amp from the beginning because my old Heartbreaker would get louder as the evening went on. I was beginning to think that I was a magnet for odd amp issues!
I definitely should have nailed it down much quicker. I've been slammed at work though and just haven't had much time to look at amps lately.

Anyway, this Saturday I will play the amp without the Patchmate. I actually put the PM on the bay. Time to get a G-System and stop messing with other stuff.

 

[dearlpitts]

well i don/t know if mine does-will let ya all know after next thursday when we play for the lompoc flower festival-which we got by winning a battle of bands contest couple months ago-which at time i did/nt have this awsome mak iii-amp-actually i have/nt even got to practice with my band yet as of the last month i/ve been plaing bass cause our bass players been gone-but hes back this weekend-yay-really not in love with playing bass.

 

[McBarry]

Hilarious, but equally good news Andy.
If it's any consolation, I/we had major panic a few gigs ago..
Lost all treble. Vol dropped a little, but zero highs..
Frigged around checking, plugging stuff in and out.. Ended up using rhythm geetarists Blues Junior for a little while, although it didn't like my pedal board too much.

Anyway, culprit was a stray footswipe onto my wah!!.
The wah has no LED and a very sensetive switch to activate. It was in "no treble" position and I didn't know...

I'm usually Mr Methodical with fault-finding, but not this time..LOL
Dave

 

[SonicProvocateur]

Lol, we've all done it. I remember posting a thread like this a few years ago when my DD3 had a dead battery or something (of course then my MKIII blew up like a week later, go figure!). But i've got a buggy wah thats my favorite that happens to sometimes never turn all the way off sometimes and keeps wah-ing and you have to stomp the mess out of it to get it to not wah and suck tone.

:lol: Some gear...

 

[Monsta-Tone]

Hilarious, but equally good news Andy.
If it's any consolation, I/we had major panic a few gigs ago..
Lost all treble. Vol dropped a little, but zero highs..
Frigged around checking, plugging stuff in and out.. Ended up using rhythm geetarists Blues Junior for a little while, although it didn't like my pedal board too much.

Anyway, culprit was a stray footswipe onto my wah!!.
The wah has no LED and a very sensetive switch to activate. It was in "no treble" position and I didn't know...

I'm usually Mr Methodical with fault-finding, but not this time..LOL
Dave

:lol: :lol: :lol:

Same thing happened to me yesterday. All of the sudden, my amp was way too bright.
The wah was on and I didn't figure it out for a few minutes! :lol: :lol: :lol:

 

[kekam35]

Easy fix guys, just make a huge album get all kinds of money and fame and have your roadie
do all of your switching for you!!!

 

[Monsta-Tone]

Easy fix guys, just make a huge album get all kinds of money and fame and have your roadie
do all of your switching for you!!!

:shock: I had no idea it was that easy! :shock:

On the positive note, I played yesterday without the Rocktron unit and my tone was very clear. The amp volume didn't move the whole day! Too bad, it was a pretty cool unit, but I think they cut some corners to get them on the market. Guess that's just the way everything is now. It's all about the money and the product & consumer just don't matter........