WEIRD behavior with Caliber .50 plus - like 'gating' effect!

Hi -I'm new to the board. and HOPING someone here might be able to give me some clue as to what might be happening. Got a new .50 cal plus head - hoping to recreate some of what I was getting years ago with my caliber .22 (that i REGRET selling!!). Well turns out it's a whole different animal with it's 6L6's - but I'd still really like to see what it's capable of. Basic function is there (and it's SHOCKINGLY loud!!-seems WAYYY louder than my old .22).

At any rate - I just purchased this second hand and didn't really hear much in the way of issues when i was demoing it... but when i got it back home I tried it out and started having some fairly major problems.

FIRST - when at low volume (esp. noticeable in the CLEAN channel) it craps out at low volume. By this i mean it does not seem to pass any signal unless a threshold is crossed and you hit it with a more aggressive strum on the guitar, after which it dies off with a very solid state crappy sounding 'distortion' or break up... I suspect I have this problem in channel 2 as well - but it's not as noticeable because it's hiding behind the dirt. Also- the clean channel seems to be FAR lower in volume than the high gain channel.

So far I've swapped tubes like crazy trying to get to the bottom of the problem (i have a ton of extra 12AX7s and 7As left over from the caliber 22 days) - i've taken out the circuit chassis and did a thorough deoxit on EVERYTHING, did the tube sockets etc... but found it didn't make much difference. The circuit board WAS rather dusty though - and there was a piece of masking tape on the chassis saying 'mesa service' - not sure if that was put there BY them or an intention of going TO them - but clearly this has been worked on before. One of the big power smoothing caps has a magic marker change date (presume?) written on it.

So I 've done everything I can think of thus far (including shorting the effects loop) short of reflowing all the solder - only because i read it's a bit of a bear to get the board out (!).

Do any of these symptoms sound familiar at all?? Would there be any other good tests to try? I'm sort of stumped here. I've googled the heck out of the symptoms and cant' seem to find much that wasn't cured with deoxit etc...

My first suggestion would be to put a cable in th fx loop.
oops, sorry didn't read your post all the way thru!

Fxrs said:

My first suggestion would be to put a cable in th fx loop.
oops, sorry didn't read your post all the way thru!

Click to expand...

yes- done. nobody else?? I probably wrote too much...

New LDR's and or Caps.

That's what happens to my amps when my power tubes are biased too cold and or is malfunctioning.

Give exact details of the power tubes you have in it. Brand, color, hardness or current rating, etc., any details you can find. If there is nothing, you may want to find yourself a set of Mesa branded 6L6 tubes with green color rating, as those are medium current tubes, and see if the problem goes away. Also, look to see if there's a power tube bias mod evident on the chassis or circuit board. Maybe you'll be in luck, and can tweak the bias to the hotter side.

Further, on occassion my working preamp tubes have basically died due to the vibration of transportation, at least on two occassions with the notoriously unreliable but incredibly toneful Tungsol RI 12AX7's. The same effect of needing a threshold signal to make them 'fire' occurs. Replace preamp tubes with new ones starting with V1.