Carvin X50B - best amp ever?

[1big1]

I played my X100B today. 23 years later, she still sounds sweet.

you don't hear a whole bunch about these amps.. but zappa really liked them for the cleans. mine could use a cap job i'm sure.

 

[MARK1970]

I played my X100B today. 23 years later, she still sounds sweet.

you don't hear a whole bunch about these amps.. but zappa really liked them for the cleans. mine could use a cap job i'm sure.

I took mine to a friend on this forum (fusionbear). He does great work. He inspected my caps and they were ok, but being it is over 20 years, I decided to have him change them. They amp had better response and more punchy. It made a difference for the good.

I do love the cleans on the Carvin. Now I have a PT100 and the cleans on there have become my favorite. The Carvin does do open chords at loud volumes with very little breakup and that is sweet.

 

[1big1]

they're cathode biased. iirc they're on the cold side when they come from the factory. i suppose they're trying to extend tube life. some folks have had them bias modded and that helped get rid of the graininess some folks complained about.

 

[simon_d]

I read that too - I believe some added a bias pot to make things easier.

 

[1big1]

yup.

 

[simon_d]

i'm running the rhythm at 3 right now. i think if i go to the lower gain input i can drive it a bit harder and it should tighten up the pedal gain and smooth it out. i'll adjust the tone controls after i try it in a different input.
i didn't really notice the graininess until i walked out front and could hear the cab at a distance where it opened up.. about 20 feet or so for a 4x12.
the tung sol i've got has fairly low gain for a 12ax7.. and isn't as bright as some other preamp tubes i've got stashed. i can try that if it's still too bright or grainy.
thanks for the tip on the presence control setting. i'll try dialing that back as well.

No worries. I'm not a fan of presence in most amps. I find the 3K EQ is better for adding sparkle than the presence which always sounds harsh to me, depends on the guitar of course. I dip the 1.5k as well, and then control overall brightness with the treble rotary but nothing major (like 4-6). So far I found the rotaries are best set nearest 5 for general purpose tones - cut the mid for metal. The amp just sounds and feels great and dones't seem to need a lot of EQ fussing.

Mine came with Mullard 12ax7s which I assume were original? (one is a Brimar), and I pulled the sovtek replacement EL34s and currently have a winged C and a Mullard in there. Missmatched on purpose as I only have the one Mullard EL34 (I read that mismatching can be good)

 

[1big1]

i'm running it fairly flat as well. bass on 6.. mids on 5.. treble and presence i think i've got on 7. could be too hot on the top end. i'll set them both back to 5 and add or subtract from there.
i just v notch the graphic for leads for the most part.
i don't think the mullards are original. iirc they were probably loaded with sovtek's at the factory.
i'm running a pair of big bottle jj 6L6's right now. when i got it somebody had stuck some small bottle peavey's in it. <barf>. i think they were trying to make it sound like a marshall.

 

[simon_d]

Yes, you're right I forgot this amp is from '91! The Mullards are bonus

BTW, how big is the OT on the X100B? Same as the power trany? The first thing I did when I got the amp is pull out the chassis and the first thing I noticed was the tiny OT. Its a 50W amp so I assume it'd be smaller but, it's less than half what I'd expected. Yet there's loads of bottom end. I'm reading Dave Hunter's 'The Guitar Amp Handbook' at the moment which says (among other things) 'more iron=more volume and better bass' as far as OTs go.

I'm not complaining just wondering.

 

[1big1]

the ot and pt aren't very large on the old ones either. i think they could get away with that because of the active eq.
i've got dave hunter's book around here.. somewhere.

 

[Ourworldisgrey]

I've almost bought an X100b a few times. All the clips I've heard sound real good, if a little loose in the low end.

 

[Anonymous]

they're cathode biased. iirc they're on the cold side when they come from the factory. i suppose they're trying to extend tube life. some folks have had them bias modded and that helped get rid of the graininess some folks complained about.

They are not cathode biased. They run class AB like Marshall's and Mesa's. Mark1970's has a bias adjust pot on the inside of the amp and I adjusted it. It sounded really great. I used to own two of those old ones back in the day...

 

[simon_d]

If this is easy to do I might try it myself. And the caps while I'm in there.

With a pot for bias can the amp take 6L6s as well, or do you have to change something else?

 

[1big1]

they're cathode biased. iirc they're on the cold side when they come from the factory. i suppose they're trying to extend tube life. some folks have had them bias modded and that helped get rid of the graininess some folks complained about.

They are not cathode biased. They run class AB like Marshall's and Mesa's. Mark1970's has a bias adjust pot on the inside of the amp and I adjusted it. It sounded really great. I used to own two of those old ones back in the day...

i haven't found a bias pot in my amp. maybe that's a change between the early version and some of the later ones.
that also makes me wonder about the pcb. mine's dipped.. not etched.

 

[1big1]

my apologies to fusionbear. he is quite right. cathode biased is class a operation.. and these are ab amps. i think what they did in this design was to use a fixed resistor to set the bias. all the trimpot is is a variable resistor.
@simon-d. i would take the amp to a qualified tech if i were going to have a trim pot installed.
also.. i don't think you can run 6L6's in place of el34's in this amp. i'm no expert.. but i think you need more plate voltage to operate 6L6's than el 34's. i've never measured the plate voltage in this amp.. but in the amps that carvin produced they usually had a switch you could flip to run one tube type or the other. if the amp doesn't have that switch chances are it wasn't designed to do that. if you are looking for a tube with more clean headroom and less break up you could substitute a kt77.

 

[Anonymous]

my apologies to fusionbear. he is quite right. cathode biased is class a operation.. and these are ab amps. i think what they did in this design was to use a fixed resistor to set the bias. all the trimpot is is a variable resistor.
@simon-d. i would take the amp to a qualified tech if i were going to have a trim pot installed.
also.. i don't think you can run 6L6's in place of el34's in this amp. i'm no expert.. but i think you need more plate voltage to operate 6L6's than el 34's. i've never measured the plate voltage in this amp.. but in the amps that carvin produced they usually had a switch you could flip to run one tube type or the other. if the amp doesn't have that switch chances are it wasn't designed to do that. if you are looking for a tube with more clean headroom and less break up you could substitute a kt77.

No prob.

EL34/KT77's are usually run at higher voltages than 6L6's, but you can use both with the Carvin. You might have to change the screen grid resistors, forgot what was in there. This is a very easy operation for any competent tech to check out when the amp is opened up.

 

[simon_d]

Thanks guys for your info on the bias pot/tubes. I'm thinking about building a simple tube amp from scratch (from a kit) to educate myself a bit more on electronics and how tube amps work. Something I've always wanted to do. Would love to be able to fix/mod/maintain my own amps.

 

[1big1]

i would suggest either finding a competent mentor or taking some electronics classes if you are going to go that route. there's a lot more to it than meets the eye.. or the ear.

 

[simon_d]

Yep I have thought about classes too but I'm quite a hands-on type. I can bias my amps and do basic remedial work but nothing that involves a proper understanding of what everything in the circuit is doing and why.

 

[1big1]

i'm pretty hands on when it comes down to it. the thing that i've found out.. the hard way.. is that there's more math formulas that i need to learn.. and skills i have to develop. my soldering skills aren't horrible or anything.. but there are guys on here that do some incredible work.
i had toyed with the idea of starting out with a very simple kit build.. something along the lines of the old early fender circuits. but money got tight after the economy tanked and i'm heading toward retirement in ten years or so.. so i'm having to re-prioritize a few things right now.
i'll continue to do what i can safely do.. but if it's over my head off to the tech it goes.
i've got an old peavey special 120 that i'd started to work on (another good sounding platform amp imho).. but there was one component i was having trouble diagnosing. i got tired of it sitting on the bench and wound up sending it back to the factory and having it refurbished. it cost 130 usd to have it done.. but the amp now sounds better than it did when i got it.

 

[simon_d]

I know what you're saying 1big1, my main reason for wanting to try a scratch build is for fun. And I'm sure i'll run into a lot of problems along the way - but as a wise man once said, problems are soluble, even if that solution means getting it to a proper tech

Back to the X50b though, it's just developed a hum on channel 2. Typical! It could be tubes as I heard a few crackles yesterday which indicates a preamp tube might be on its last legs. Not sure what else to look at if it isn't - maybe giving it a good deoxit on the rear switches (I only did the pots). Ha, I could do with some amp diagnostic skills now!