Ive had the mark V over a year at this stage so im fairly up to speed with what it can do.I bought it used, and the previous owner said he had replaced the V1 tube with a JJ.I replaced this earlier in the year with a mesa boogie spax 12ax7.Recently the gain channels have been bugging me.They don't seem as responsive as they were when i first got the amp.Particularly when it comes to sustain.It seemed to just sing forever when i first got it but now it just sort of dies unless the gain is up almost full, and even then its not as touch sensitive.Now im not using high gain pickups but i do have a clean booster pedal to get more output if needed.Im using the same guitar etc as before so thats not the issue.I do remember when i put in the boogie tube, the amp seemed to have a little less gain(hard to do a quick A/B test),which i was happy about as it meant the clean channel sounded a bit sweeter.Anyway,recently i guess ive only come to realise that gain channels aint wot they used to be.Ive always felt it i guess, but its just clicked recently.Before I couldnt put the guitar down as it was addicive,now it feels a bit unresponsive.Now im presuming its the tube change that has caused this.Does anyone else use stock boogie tubes in the preamp and feel the sustain is a bit weak compared to other tubes they have tried?Could it be the power tubes goin?I havent been driving the amp hard or anything as its mostly low volume and up occasionally for recording.Just doesnt seem right anyway.Now i still have the JJ tube,so i can stick it back in and see.Its a bit of a job replacing tubes though so i thought id post here first.Cheers.
Gain channels not sustaining much
- Thread starter diddlydan
- Start date
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jb's 52
Well-known member
I'm using stock pre amp tubes and the sustain is comparable to the Mullard's, Tungsol's, and EHX's I've tried in there as well. The differences I usually hear revolve around clarity and voicing. If my amp starts losing it's responsiveness and "umpff," the power tubes are the first place I go. If my amp isn't sounding right and my power tubes are roughly a over a year and a half old, I change 'em.
Yes, i suspect that might be the case.I havent been driving it hard now but its on most days.Im not sure how much use it got from the previous owner either.Guess ill pick up a set and swap em out.If its not the power tubes,theres no harm having a few spares anyway.Cheers
I would agree, power tubes. Order a new Rectifier tube too (that will not cause gain to suffer though but recommended to replace it with power tubes).
If you can afford it, may as well get new preamp tubes. I actually prefer the Mesa 12AX7 in the all of my amps. I have boxes of the other tubes but I rarely use them. I have them on reserve if needed.
If you can afford it, may as well get new preamp tubes. I actually prefer the Mesa 12AX7 in the all of my amps. I have boxes of the other tubes but I rarely use them. I have them on reserve if needed.
elvis
Well-known member
Be careful with the SPAX7. My experience with those has been that they have quite low gain. Throw a standard 12AX7 in and see if it doesn't pep it up.
screamingdaisy
Well-known member
The stock Mesa preamp tubes are JJ ECC83s. The SPAX7 is a stock Mesa tube that tests exceptionally well for low noise. Assuming you didn't pick up a tube that was lying around on a shelf somewhere for 10 years that means it's most likely a JJ ECC83 as well.
The previous owner replaced the stock JJ with a JJ. You replaced his JJ with another JJ.
But I'll echo what the others said... if it feels like you're loosing power, your attack is dull, you keep increasing the treble and master volume while lowering the bass... your power tubes are probably shot.
The previous owner replaced the stock JJ with a JJ. You replaced his JJ with another JJ.
But I'll echo what the others said... if it feels like you're loosing power, your attack is dull, you keep increasing the treble and master volume while lowering the bass... your power tubes are probably shot.
elvis
Well-known member
screamingdaisy said:
It may be a stock Mesa tube, but my experience with several (at a huge price premium) was that they were anemic. My hypothesis is that the weak ones test well for microphonics and noise. I'm curious if anyone has ever tested SPAX7 vs 12AX7 for gain on a tester. I... haven't.
:?: :shock: 
JJ tubes are not Russian or Chinese, they are Czech Slovakian. The other brands sold by new sensor are Russian (brand trade names: tung sol, EH, Mullard, Svetlana, etc....) made in Saratov Russia.
I actually like the SPAX7 as it cuts down on the ice pick of the Mark V a bit. Still a bright amp. I have not noticed any sustain issues using SPAX7 in V1. Same would apply to the Roadster as it seems to reduce some of the low frequencies. Sure the tube may have reduced gain but it still is in the 12AX7 range.
What may matter is the condition of the PI tube. Also note that the Mark V shifts the applied plate voltage of the 12AX7 of several of the tubes in the gain chain depending on what channel is in use. Depending on age of your preamp tubes, may be time to change them, not just one but all of them. Keep the one's you have removed as spares in the event you need one or get a noisy tube issue.
JJ tubes are not Russian or Chinese, they are Czech Slovakian. The other brands sold by new sensor are Russian (brand trade names: tung sol, EH, Mullard, Svetlana, etc....) made in Saratov Russia.
I actually like the SPAX7 as it cuts down on the ice pick of the Mark V a bit. Still a bright amp. I have not noticed any sustain issues using SPAX7 in V1. Same would apply to the Roadster as it seems to reduce some of the low frequencies. Sure the tube may have reduced gain but it still is in the 12AX7 range.
What may matter is the condition of the PI tube. Also note that the Mark V shifts the applied plate voltage of the 12AX7 of several of the tubes in the gain chain depending on what channel is in use. Depending on age of your preamp tubes, may be time to change them, not just one but all of them. Keep the one's you have removed as spares in the event you need one or get a noisy tube issue.
