Power tube mix question and tip

[pgrudge]

Recently retubed my Dual Recto 2ch revC, serial loop. The preamp sound i was after was found in Tung Sol reissues and JJ's.

For the power amp i decided to try out JJ6L6's and was happy with the sound until i goofed up real bad when reaching back to turn down the FX-send a little and accidently grabbed the FX-loop selector and during a split second chose bypass loop! I had an open D ringning from my guitar at the time and BAM, full volume! I am usually very careful and still can't believe how stupid i was! Of course the power tubes started to make cracklenoise and pops after that accident and i decided to find the pair that was popping the most and put some of my old sovteks in...

To my surprise the whole amp cleared up in sound and gave me a much more complicated tone than i would've thought possible. The only words i can use to describe the sound are 3 dimensional....


Now i wonder if anyone else has got a good mix of 6l6-pairs that give the same result? I was thinking of trying a quad of SED 6l6's next retube, but maybe i should just buy 2 and mix it up! Tell me your thoughts!

 

[mikey383]

As long as you keep them in pairs...XYYX....you're good to go. And I'm not even certain that applies. Amps back in the day didn't run with matched quads.


I tried 6L6s and E34Ls in my Dual Rec once. While I liked the tone very much, I just didn't feel right doing it.

 

[94Tremoverb]

Mixing 6L6s and EL34s isn't a good idea because you can't bias all four right... either the EL34s will be so cold they're basically off (switch set to 6L6) or the 6L6s will run far too hot (switch set to EL34). You can probably get away with it in EL34 mode if you have the amp set to Spongy, or possibly Bold/Tube depending on the 6L6s, but if you're going to try it you really need some means of checking the tube current and plate voltage.

But mixing four of one tube type is fine. Two matched pairs may work best, or maybe not... but you can't do any harm, since Mesa's stock bias is cold enough that almost no tubes will run too hot, so you can mix and match however you want. Like mikey said, back in the day no-one bothered about matched sets. There's some evidence that unmatched sets give more interesting harmonic distortion too.

I've done that accidentally switching off the loop with the channel master set right up thing too . It's pretty funny (in a Back To The Future sort of way)... although you shouldn't really have blown a tube just by doing that, the amp isn't running them any harder than it would normally at high volume. I didn't blow any of mine.

 

[pgrudge]

Yeah i didn't think it would cause any harm either, but when the amp started popping and crackling i had an idea what had happened My ears were still ringing, haha.

I think i've read that somewhere....Turn everything to 10, tap the poweramps with a wooden stick and the ear that starts ringing is the bad ear... :roll:

 

[mikey383]

I think i've read that somewhere....Turn everything to 10, tap the poweramps with a wooden stick and the ear that starts ringing is the bad ear... :roll:

:lol:

Mixing 6L6s and EL34s isn't a good idea because you can't bias all four right... either the EL34s will be so cold they're basically off (switch set to 6L6) or the 6L6s will run far too hot (switch set to EL34). You can probably get away with it in EL34 mode if you have the amp set to Spongy, or possibly Bold/Tube depending on the 6L6s, but if you're going to try it you really need some means of checking the tube current and plate voltage.

That's one of the reasons I didn't run with it. I put a bias pot in my DR right before doing this, and I couldn't get them in a suitable range. If sounded good, but IIRC, the coldest tube was getting around 12mA while the hottest one was ~50.

 

[94Tremoverb]

That's actually just about OK, depending on what the plate voltage is, ie which power supply mode you're in - I guessed it would be more extreme than that. Without a bias pot (which I fitted to mine too), the voltage and current in the Spongy modes are really low, and the tubes only run at a few watts - that's why I fitted the pot. And even 50mA is OK if the plate voltage is less than 400V - which it is in the Spongy modes. As long as the tubes are running somewhere between about 5W and 20W, it's safe enough. I think I may have to try this now!

I already sometimes run the amp with 6L6s and the switch set to EL34, if it's in the Spongy mode. Basically I just use the tube switch as a warm/hot switch. I even swapped the LEDs round so the FX loop light on the front is green and the 6L6 light is orange, which I think looks much better .

 

[mikey383]

I had them in bold/diode mode with around 478 plate volts.

I don't recall exactly what the measurements were (It's been quite a while since I did it), but I remember they were somewhere around that area with the bias set to factory. I remember if I went any colder, one set would have been way too cold, and if I went any higher, the other set would have been way too hot.

Before I put the bias pot in, I was running a quad of JJ E34Ls at around 60mA! :shock: Ran those for nearly 3 years without any problems. They didn't redplate at all either. I finally got around to taking measurements and was shocked to see they were drawing that much. Sounded great though. I've never had so many compliments on my tone.