I tried the reissue Mullard EL34 .....

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by GuitslingerTim, Dec 28, 2005.


  1. GuitslingerTim

    GuitslingerTim Member

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    A matched pair of Mullards arrived yesterday along with a new pair of SED EL34's, and four new EHX 12AX7's.

    The first thing I did was turn the bias pots on my DSL50 to the lowest settings and check the power levels with the new SED's installed. The old set of SED's in the head would go as low 34mV and 39mV for each tube. The new ones went as low as 32mV and 35mV, which is good, I've been shooting for an ideal setting of 35mV per tube but could never quite get there.

    In comparing the Mullards to the SED's, the Mullards appeared to have longer pins, which turned out to be correct--it took a little extra push to get them to seat properly in the sockets. The only other notable visual difference is the absence of the pretty blue glow the winged-c's emit.

    The real surprise was the readings that registered with the bias pots zeroed: 28mV on the left side, 26mV on the right--that's about 10mV lower than the lowest values for other tubes used in the past. Another oddity compared to other brands is the left tube registers higher than the right, just the opposite of other brands. Maybe someone with technical knowledge of power tubes and amps can chime in and explain the practical difference as to why the Mullard reissues act so differently. For instance, are the lower current readings a sign of better or lesser quality?

    After installing the Mullards I also changed out all four preamp tubes so as to eliminate any factors that might detract from the tone of the power tubes. The downside in doing that is that making a fair comparison between the Mullards and the SED's requires installing the new SED's and testing them in the same environment, which will include lowering the bias settings to 35mV.

    Set at 35mV per tube the Mullards sound very nice. They seem to be much darker than the old SED's, but again, that might be one of several qualities attributable in part to the lower bias settings, or the new preamp tubes. Two qualities that stand out is substantially increased detail/definition, and a pronounced sweetness that might surprise a lot of people coming from a DSL50.

    Tomorrow I'll stick the new winged-c's in and make a close comparison to the Mullard reissues and try to narrow down any tonal differences. My initial impression of the Mullards is entirely positive, and worth the extra $7 paid for a matched set
     
  2. CJReaper

    CJReaper Member

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    I just put a pair of the New Sensor Mullard EL 34s in my Marshall 2204 (1982 JCM 800, stock) and they made a big difference!! My clean tone is actually really good now, and my crunch sound is better than ever. I’ve heard others say it’s just a re-labeled Sovtek tube, I don’t think so! They may not be NOS but I’ve never heard a Sovtek tube sound this good, I highly recommend them.

    Cheers,

    CJ
     
  3. Blue Strat

    Blue Strat Member

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    Varying bias numbers are not an oddity at all. Think about it. Why do we order matched pairs? Because tubes of each type/brand (eg, SED EL34s, Sovtek EL34s, etc) can vary in idle current by a substantial amount. You could buy another pair of the same tubes and get completely different readings.

    As for which socket gives you the higher reading, swap sockets and the opposite socket will be higher. ;)
     
  4. daneswede1

    daneswede1 Member

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    I also had Mullard EL34 Reissues installed in my Marshall 2203x reissue JCM800. THey do have a tight response. I am going to open them up tomorrow night at rehearsal for the first time. Then ill see what they are really about. Mt tech uses them in all there pt to pt amps they build. at Industrialamps.com
    He also installed some new production Tungsol 12ax7s. I have yet to really check the tone but will update this !
    My 1981 JCM800 has Svetlana C Wing EL#4s which I just love! Very spongey and warm mids. Great tone. Probably my favorite new production EL34 that ive tried yet. Have a quad set of Siemens EL34 NOS that im saving for the 81 2203 JCM80 0when the svets run out of gas!
     
  5. GuitslingerTim

    GuitslingerTim Member

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    Before comparing the new Mullards to the SEDs I increased the bias adjustment to the factory specs of 45mV and was pretty much knocked out by the tone of the Mullards. The real difference between the Mullards and SEDs is the Mullards emphasize the upper-mid frequencies which produces better note definition. While playing lead runs I had to stop and repeat a few notes just to make sure what I was hearing wasn't speaker rattle--it was percussive attack caused by my picking action, and not something I'm used to hearing. The added detail is pretty nice for lead guitar work, but the SED's are better for rhythm work that requires more thump.
     
  6. MrMo

    MrMo Member

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    I'll preface this by asking you to forgive my technical ignorance. Although they still sound pretty good, I feel it may be time to change the EL34 tubes in my DSL50. One of them simply stopped working and I replaced it with another tube of a different brand that I had on hand. First, can using non-matched tubes, as I have, be detrimental? Second, when I replace them, is re-biasing necessary? Last, can you let me know where the Mullards are available or suggest other good sounding replacements? Thanks in advance for any help!
    Mo
     
  7. GuitslingerTim

    GuitslingerTim Member

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    One of the advantages of owning a DSL is the ease of setting the bias and changing the tubes out.

    As far as the detrimental effects from tube choices go, I'm not knowledgeable enough to say.

    When replacing tubes it's better to rebias for optimum performance. If the bias happens to be way too high it can shorten the life of the tubes and have an adverse effect on tone.

    I ended up lowering the bias to 40mV per tube on the Mullard reissues, and as is the case with the SED tubes, I like the sound much better than the factory setting of 45mV. The tone produced by both brands is similar, with the SED being a little fatter, and the Mullards a little more defined. The SED cost $7 less per matched pair than the Mullards.

    If you're willing to purchase a digital multimeter that measures DC volts you can set the bias yourself by simply removing the back grill and measuring the voltage using the three test pins that protrude from the chassis. The center pin is ground, the left pin corresponds to the left power tube, the right pin corresponds to the right power tube. There are two small bias pots that have to be adjusted with a small screwdriver in order to change the bias settings. As long as you avoid touching the pins, or better yet, engage the standby switch during adjustments, the procedure is safe.

    I cut two short pieces of 1/8" dowel rod that are wedged between the locking rings holding the power tubes and the top of housing. The rods are short enough they can be wedged in place and open up the rings just enough so the tubes can be wiggled out of the socket. I'll add that you should never attempt to remove the tubes when the amp is turned on, or even plugged in, and never disturb the tubes when they're warm, it can damage the filaments.

    I get my tubes from Triode Electronics, and to their merit I've yet to get a bad tube from them.

    http://store.triodestore.com/tubes.html
     
  8. Crunchyriff

    Crunchyriff Member

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    GunslingerTim: You have touched on one of the 'little secrets' that really bring the DSL series to life. I've got a close friend who is quite a techie (I'm not- I'm just a player pretty much), and he was telling me that actually LOWERING the bias on the DSL's from their factory-set 45mV is one key to making these amps really sing. Funny- it goes against the grain of most the common procedure for tweaking new amps as they usually set the bias LOW from the factory, to help give them a cushion in those 90-day tube warranty claims...so they set em a bit cold. Not here.
     
  9. EADGBE

    EADGBE Member

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    Which tubes have more harmonics? More sustain? Which are quieter? Which have more crunch? Which are louder? I have SEDs in my TSL right now.
     
  10. GuitslingerTim

    GuitslingerTim Member

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    I have to give the edge to the Mullards in the areas of harmonics, crunch and sustain. I had 'em singing and squealing tonight.

    I'm not sure which of the two brands is quieter, both are quiet in my rig.

    I'm also unsure how you tell one set of tubes is louder than another when using a Marshall halfstack. :D

    The only thing I can say about the SED is they sounder a little bigger and fuller than the Mullards, and they last a long time. The added definition provided by the Mullards has become more apparent as I've used them the last couple of weeks. I may become a convert if they hold up.
     
  11. Geetarpicker

    Geetarpicker Member

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    I didn't have good luck with the new Mullards. I copied this from a note I left over at the Plexi forum. Maybe others will have better luck with these tubes. I thought they sounded very good, but sadly only for a short while.
    ________________________________________
    Pardon the long post.

    The short version: New Mullard EL34s only lasted about 2 hours. And the common mod to reduce B+ (a little) by rewiring the input of the PT had some side effects...

    Just went through a long weekend of tweaking that kinda went for not. I have a '68 Plexi (cabs down under) Dagnal tranny Superbass 100 and was looking to sweetin' the slightly harsh high end somewhat and thought I'd try some other output tubes. Currently the amp is quite reliable with a set of EH EL34s, though they are a somewhat unbalanced set. 2 @ 35ma (480 B+, 44v bias) while the other 2 run @ 25ma. Put one on each side and at least it balances out. Tubes have about 2 years on them.

    A local shop actually let me "try before I buy" some EL34s. I brought my Plexi and a bias checker with me. My tester is a inline socket deal, that breaks the main ground of the tube and allows me to put my Fluke meter in line. Currently the amp is setup to run EH EL34s, and are set @ 35ma per tube @ 480 B+. First I swapped in some new JJs. Without changing the bias they were right at 35ma, but sounded very similar to my EH tubes. I was looking for something different. Then I tried some of the New Sensor Mullard EL34s and they first came up at about 22ma. So I opened up the amp and set it up to 35ma per tube. I checked each tube, and the set was nicely balanced. The sound was noticably darker, and sweeter than the EHs so I took the "new" Mullards home. I know they weren't old German pieces AT ALL, but the tone did impress me.

    Well, I kept a close eye on the tubes and after the 1st hour I noticed just one was just starting to red plate (very slightly) under heavy playing even though they were still holding 35ma bias. They were only slightly red plating under full load, but would settle down at idle. Since the amp runs fine with the EH tubes I decided it was probably that the new Mullards just can't take much B+. SO I decided to try the quick and dirty PT wiring mod to reduce the B+. After wiring up the PT using the 120 & 245 tap wires (instead of "common" and 120v) I was able to get the B+ down to a nice 444v when biased @35ma running about 40v B+. Then the Mullards seemed happier, the tone was even sweeter and the red plating was gone even under full load. The filament voltage still came in at 6v, so all seemed well. After another hour of playing the amp hard the tubes went south. I guess too much heavy handed playing with the amp cranked running a Fuzz Face put the tubes over the edge. The set of tubes started sounding weaker, and would not hold bias. 3 out of 4 of them started to run away, albiet slightly. They were then pulling about 50-60ma per tube and would not respond to the bias trimmer at all to bring it down. At first I thought something had gone wrong with the amp. I let the tubes fully cool and set the trimmer at max bias voltage and tried them again, still no go as they would start to run away. I then put in my 2 year old set of EH tubes and the amp played fine and biased right up with total consistency. So, the new tubes were toast. Even with only an hour @ 480v B+ and another hour at only 444 B+ both set up at 35ma per tube.

    After putting the EH tubes back for a while I noticed some heat issues with the power transformer. It seemed the wiring mod just wasn't quite working out to reduce the B+. Some have said the upper end of the PT primary is of a thinner guage and can't handle the (120v) load as well when it runs in the modded state. I believe that now. When using the taps for 120 & 245 as the main hookups the tranny in my amp does run hotter, and you can see more modulation (slight flashing) of the power light as the tranny saturates and apparently also sags the filament wind. Sure the amp normally pulses the pilot light a tad when fully cranked, but it did so much more noticably with the mod.

    SO, all that said I put the amps tranny back to it's original wiring and put back in my same old pair of EH EL34s. Set the bias back to 35ma and all is back to normal.

    Amazingly the store gave me credit on the Mullards, and I just swapped them for a spare set of EHs that I at least know will work. Maybe I should have swapped back for the JJs, though I'm not up for another tweak session yet. I really wish the Mullards had worked out, as to my ear they did sound nicer than my EHs. It's a shame they didn't last the day...

    Maybe someday I try the JJs again, but for now I'll leave well enough alone... for the moment at least [​IMG]

    Sure my old Plexi deserves some nice NOS tubes, but for now I'll stick with the EHs. At least they work and sound pretty decent.

    Guess we sometimes have to go back to go forward. Tweak, learn, tweak, learn...repeat...

    Cheers fellow tweakers!
     

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