Post by hammerheadmusicman on Jul 11, 2012 16:40:22 GMT -7
I am a gig on a cruise ship for 2 months, and I've noticed the jnr starting too loose a little headroom.. Bothe the VOL and MV are both on about 12 o'clock..
I have a 60's Dutch mullard ecc83 in V1 and a 60's English Brimar in V2, I have some groove tubes el84's In the output stage (I've recently bought some 60's mullard 84's but didn't have time to have it biased before I came on the ship and when I put them in they were a bit 'glowy').
I have three spare mathed pairs of JJ 84's with me, and a ton of 12ax7's (all recently tested by my amp tech), so I'm going to do some testing in the morning..
I guess my two questions are
A) do you think it could be preAmp stage or output stage? B) have I just got it set up like an idiot, and should I have the MV down and the master up to gt a cleaner sound?
Post by benttop (Steve) on Jul 11, 2012 16:54:59 GMT -7
Well first off, you do not have to have your Maz Jr biased - it is self biasing. Just make sure the power tubes are matched pairs. And the only thing to be concerned with "glow" would be if the plates are glowing. Otherwise, ignore the lights behind the curtain.
Second, I'm betting your problem is in the power tubes, but just about any tube can cause you problems. The ONLY reason I choose the power tubes is because they wear out so much faster than the others. And when they wear out, it definitely affects tone and dynamics.
Third, if you put the master full up you're going to get more headroom, but you also get some power amp saturation that you may or may not want, depending on how loud you're playing. Only you can judge for sure. Just twist it up a bit and try it.
Post by hammerheadmusicman on Jul 12, 2012 2:01:49 GMT -7
I say 'have it biased' because the guy who had it before me had taken it to an amp tech, who had without telling him changed the cathode bias resistor for one which was running the output section fairly cold.. So much so that my amp tech said the output valves would literally last forever. So he tweaked it up to be closer to where it's supposed to be, and now it sounds great, but I think it is running them too hot for the mullards as they were glowing (plates) only slightly, and as they are quite pricey vintage valves I didn't want to risk damage to them or the amp itself.. Good call on saying output section, now you mention it, on the last few nights I seem to have been having to crank the volume a little more every night..
Post by hammerheadmusicman on Jul 12, 2012 8:11:58 GMT -7
I have put in the JJ's that came in the amp, and it sounds loads better, they aren't quite as warm though.. A little brittle sounding. That the last times buy groove tubes 84's, the are a few months old but I have only done maybe 9 gigs with them, and they don't get used muchat home, and when they do they don't really get pushed!
Post by benttop (Steve) on Jul 12, 2012 8:59:36 GMT -7
You may be surprised to learn that with this design the tubes are running hot even if you are not playing. If the standby switch is off, the tubes are wearing out. You may get a bit more life if you play more.
Post by hammerheadmusicman on Jul 12, 2012 10:15:38 GMT -7
That is interesting, so in standby mode, just the heaters are on? Then as soon as you switch it on fully the cables are being pushed? So should the old leave it to warm up an hour or two before the gig rule go out the window?
When your power switch is on (up) and the standby switch is down, all that is running is your heaters on the tubes. When you turn standby off (switch up), you then have high voltage on your tubes and that is when they are running hot and wearing out - even if you are not playing. I hope that makes sense!
You only need to warm your amp up for 60 seconds or so before you flip your standby switch up to play. You don't need to warm your amp up for an hour before the gig. HTH, jw
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Post by hammerheadmusicman on Jul 23, 2012 10:53:15 GMT -7
Is that the resistor value for the output valves? I realise my post may have been misleading, I meant 'pre refined Maz' as I don't know how different they are internally.. Thanks again guys, and doc, this forum is great
Post by hammerheadmusicman on Jul 24, 2012 10:25:41 GMT -7
Thanks for your help Doc your customer service is excellent
When I bought the Maz, the previous owner had taken it to a tech for a repair, and for some reason the tech took it upon himself to change the cathode bias resistor to 350ohms?!
So when I bought it I took it to my amp guy for a service, and he said the output section didn't sound 'quite right' so he put a 100ohm in.. Would this affect the headroom? Would you recommend putting 150ohm back in it when I get home?
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