MA100C issues

[SteveD]

Welcome to the forum pacAir.

The amp should easily reach the bias target of 76mA per side with room to spare. Sounds like there is a more deep rooted issue.

[pacAir]

Thanks! The amp now CAN be biased properly and the interaction of the two controls is more predictable and less "squirrely". I underestimated the effects that 2 pair of unmatched output tubes can have. I normally don't do this but I didn't have a new matched quad of EL34s at hand. Since the amp came to me with a bad factory tube I opted to replace a whole pair for new rather than substitute a single used tube. This turned out to be the root of all the problems I first saw.

As it turned out, using the single used tube work much better! This amp now has a lovely clean channel unlike any other Marshall amp I have personally owned (JCM800, JCM900, Haze 40). In my book, it has to have a great clean channel and take pedals well to start with. You can take this amp anywhere because it does have a great clean channel, at least on my "clean standard" (American Strat on the neck pickup).

Steve

[Nebulozny]

I think I might have some volume issues too. Am I just being too negative or 100w valve amp should blow drummer away easily but it seems MA100c is having hard time doing it. I am playing against second guitarist Behringer SS 60w amp and have to push gain channel more than 3' clock
Clean headroom should be more than I have now, could this be same problem pacAir had with output tubes? I also own Roland JC-160 ss amp, 120 watts and volumes this thing puts out are devastating, I just haven't felt this with my MA. How can I measure RMS output ?

[SteveD]

The MA is deliberately voiced on the darker side which will always sound less loud than trebly amps. Plus the combo is only driving two 12" speakers. If you want more volume there is more on tap by putting a boost pedal or an EQ in the loop. This works great for a solo boost on the MA, give it a try.

[Nebulozny]

I uderstand it's only 2 speakers, but in my opinion 100w trough 2x12' should be more "in your face" , but maybe it's that darker sound that makes it apparently less loud. At home it is more than loud but in rehearsal room it seem to get lost in the mix with other bandmates, I was thinking about another 2x12' cab to hook up, more headroom.
I will try boost in the loop trick, damn those drummers , the guitar against drum war will never end. :Pirate2

-- Tue Aug 10, 2010 7:52 am --

Well, I tried your boost in effect loop trick Steve, what a change in sound. I have no clean boost pedal, so I tried Boss SD-1 overdrive, with volume on full and drive on zero, gain channel sounds so much better now.
Can you explain why this volume boost makes such drastic change in sound and distortion, power tubes break up early or ? SD-1 is now ON all the time in the loop, for solo I just switch to boost.

[PS1984]

My problem was actually 3 weeks ago. I have 100 combo

i was with band right in middle of practising - played on OD channel volume 5, and suddenly the combo went silent. No sound - like MUTE knob on TV; One tube was totaly orange. very much orange. (from left to right > it was the 2-nd one). So I turn OFF the amp and I wait about 30 minutes. Then I turn it ON again and again no sound..

Maybe 2-3 month before this my tubes had on glass blue strap. and tubes did rattle - i mean something glassy sound.

I used this setting on OD channel - Crunch balance - 12´o clock; Gain 12´o clock; Bass - 15´o clock; Mid 13´o clock; Treble 14 o ´clock; Reverb 11 o clock; Resonance - not use; Presence 14 ´o clock..

What is the problem?, What can I do now? I really like my combo. This is my firt Marshall experince so I hope it will not be my last. I really like the sound.

Please help

[SteveD]

Welcome to the forum PS1984.

Looks like one or more output valves have blown and probably the internal HT fuse too. They need to be replaced and at the same time I would recommend you get a tech to check that the bias is not too high.

[PS1984]

Welcome to the forum PS1984.

Looks like one or more output valves have blown and probably the internal HT fuse too. They need to be replaced and at the same time I would recommend you get a tech to check that the bias is not too high.

thank you.

Combo is still under warranty so can I take it to the shop and change it in that way??

[surfnorthwest]

The tubes carry a 90 day warranty, I would take it to a authorized Marshall service tech and have it checked out. If the problem is only the power valves you should be in and out of there in an hour with new tubes and a bias.

[PS1984]

The tubes carry a 90 day warranty, I would take it to a authorized Marshall service tech and have it checked out. If the problem is only the power valves you should be in and out of there in an hour with new tubes and a bias.

thank you