DGMDT 2-Channel Amp... Ultimate Club Gig Rig?

[Boogie]

Aristotle, I meant to ask you this earlier...in your PRS amps that have them, what brand EL34s do you have? Have you had to replace any since you bought the amps? Just curious...

 

[aristotle]

Actually, I've never replaced tubes yet in either the MDT or HX/DA. Stock tubes in both....and I'm not even sure what they are. I have experimented with lots of NOS stuff in my Marshalls, but with EL34's, I tend to go Tungsol. That's mainly because I hate rattle and Tungsol seems to rattle less. My MDT is rattling like a can of pebbles at the moment, so I'm about ready to do something about it. In live situations, rattle isn't an issue of course, but playing at home it just bugs me. NOS Mullards do sound nice, but I'm not sure that's not in part due to the fact they cost a bunch, and I'm ready to buy into it...

 

[jfb]

Let us know what you decide to get.

:biggrin:

 

[László]

The HXDA came with Winged C EL34s that are now out of production, but available as NOS at most tube dealers. I like the tone.

I bought a spare set of NOS EL84M tubes for the DG30, 80s Russian military. Word is that they'll sound even better than the stock Sovtek EL84Ms, but I'm not going to replace the stock tubes until they show some signs of wear because I'm pretty happy with where they are.

I haven't had tube rattle in the HXDA or DG amps. I do keep amp heads separate from cabs on a rolling cart so I can move them near my workstation, so maybe that's why, but in the past I've had tube rattle just from the head being in the same room as the cab, so I get where you're coming from Aristotle. I'm lucky not to have the rattle, I guess, though it's possible that having acoustic treatment in my room helps to absorb some of the low end resonances that create tube rattle in the first place.

In the past I've tried Sorbothane feet to isolate heads, though you can get staining on Tolex so you have to protect the surface.

 

[Boogie]

Mine came with =C=s, too, and just had one red plate on me. In 30 years of tube amps, I've only had 2 power tubes red plate and both were EL34s. Thankfully the fuse blew and protected the screen grid resistor, so no collateral damage...I don't think. The spare JJs seem to be ok but that's tough to qualify now that the SEDs are dead. NOS may be the route I go, but I've never bought old power tubes so it will be an adventure (I have NOS preamp tubes out the wazoo!).

Aristotle, tune rattle has been a problem for me, too, even with the SEDs. The bass response of this amp is brutal on the head, so I put the on the ground when it bothers me. I've heard that the EL84s in the 30w HXDA combo rattle horribly. Mesa/Boogie tackled that issue by using a suspension system they called the SUS-4 and it worked beautifully. It isolates the chassis from the cab and I've never had an instance of rattle, even with the massive EV speaker right next to the amp and tubes. Two stripes of very high density foam (Dell ships their servers in it) between the head and the cab worked wonders, too.

 

[László]

Mine came with =C=s, too, and just had one red plate on me. In 30 years of tube amps, I've only had 2 power tubes red plate and both were EL34s. Thankfully the fuse blew and protected the screen grid resistor, so no collateral damage...I don't think. The spare JJs seem to be ok but that's tough to qualify now that the SEDs are dead. NOS may be the route I go, but I've never bought old power tubes so it will be an adventure (I have NOS preamp tubes out the wazoo!).

Aristotle, tune rattle has been a problem for me, too, even with the SEDs. The bass response of this amp is brutal on the head, so I put the on the ground when it bothers me. I've heard that the EL84s in the 30w HXDA combo rattle horribly. Mesa/Boogie tackled that issue by using a suspension system they called the SUS-4 and it worked beautifully. It isolates the chassis from the cab and I've never had an instance of rattle, even with the massive EV speaker right next to the amp and tubes. Two stripes of very high density foam (Dell ships their servers in it) between the head and the cab worked wonders, too.

Unfortunately, Mesa doesn't use the SUS-4 system any more as far as I know. I had it on my old Tremoverb, and it worked very well.

I think the 30 Watt HXDA is not EL84 but EL34, just like the HXDA 50. They're simply running the tubes differently, cathode biased instead of fixed. Generally, what rattles like crazy on an EL84 is those spindly little tube retainers most manufacturers use. In most cases there's a clip that springs on top of the tube and holds it by the nipple (EL 84s have nipples and yes I said nipple because I'm a dirty minded guy). But its not tight enough against the tube, and the metal spring tends to rattle against the tube's top.

 

[Boogie]

Yeah, I think you're right about the 30w HXDA being EL34. I figured Dirty Bob would come in and correct me here, but he must be busy building another Thorn. :biggrin: Those coil spring retainers always seemed useless to me since a well maintained socket will be fine on its own, even if the tube is inverted. Regardless of the original source of the vibration, the power tubes were resonating enough to be audible thru the amp. All of this, though, was at substantial volume and moving the head to the floor eliminated the problem.

 

[László]

All of this, though, was at substantial volume and moving the head to the floor eliminated the problem.

That it will do, but at my age bending to the floor to adjust the amp would be a fate worse than tube rattle.

So what if I'm so old I had to put my amp head on a rolling cart to move it around in the studio...

 

[Boogie]

When I'm going to be standing up, bashing on a guitar for 4 hours, hopping around, dancing and otherwise destroying my knees on a Saturday night, the last thing I'm worried about is bending over to tweak the amp. You, OTOH, have the luxury of comfort, so why suffer? The cart is brilliant.