What EL34's will handle high plate/ screen voltages?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Greazygeo, Jan 2, 2006.

  1. Greazygeo

    Greazygeo Member

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    I have an old Orange 120 watt head that came with Mullard EL34's. They need replaced (only running a pair) and I don't know what I can get to replace them. I tried a quad of SED's and they work until the volume is past halfway then the mains fuse pops. With the pair of Mullards, the fuse won't pop and the amp works fine.

    Biased at 32 -34 ma the PV's are approx 520 with the screen being 1 volt less.

    How about the GT 6CA7's? That's what I am leaning towards a t the moment....

    Thanks,

    George
     
  2. Broken

    Broken Member

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    It might be worth having a look at the new JJ KT77
     
  3. Igneous

    Igneous Member

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    try the new sensor mullard re-issues. they can handle a huge load!!!
     
  4. Roe

    Roe Member

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    jj e34l tubes [sic]
     
  5. shakti

    shakti Member

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    It's a boring answer...but do yourself a favour and get NOS. You will save on it in the end, and have better tone in the meantime. I recently had to scrap to halves of supposedly matched quads of JJ and SED tubes in a Super Lead since those tubes popped like tired light bulbs. That was brand new out of the box. Now I'm left with a pair of each. Expensive lesson.

    If you shop around for a good tube dealer, you can get a nice quad of NOS Tesla or even Mullard for less than 200 or thereabouts. Sounds expensive, but if you buy from a standup guy who backs his product, how can you go wrong? The will no doubt last much, much longer than new production stuff. Try Terry Kilgore (www.tubetramp.com). With 520V, that's all I would trust to put in there.
     
  6. shakti

    shakti Member

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    Correction...I said NOS Mullard, but that would be used/testing excellent. NOS Tesla is another story, you may be able to find those for 200.
     
  7. VintageJon

    VintageJon Member

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    If it's an EL34 it's spec is 2KV on the plates.

    I would go with JJ E34L's if it were in my shop.

    -Jon
     
  8. Dai H.

    Dai H. Member

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    consult with a tech who is familar with those amps and make sure it's not the amp. You say the amp didn't pop the mains fuse with two tubes and did with four. That's double the heater current and more also on the B+ line which would seem to make it more likely to pop a fuse as opposed to running on two power tubes. I seem to recall seeing some blurb about some old Oranges not running well from inadequate bias supply. So make sure it's not something to do with increased current draw from having more tubes plus possibly something else (such as inadequate bias or whatever). Otherwise, you may still have the same problems even if you use four NOS instead of two.
     
  9. VintageJon

    VintageJon Member

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    Yeah, check the bias as it may be a bit off in older Orange.

    Hi Watt was better known for for too hot bias and I've usually had to build voltage-doubler for them. Same for Nolan, now there's an obscure British unit I've seen a few of...

    Blowing mains but not HT is strange, but may be EL34 has failed. Be damned sure that HT fuse is correct...

    Does it blow fuses with EL34's removed?? If it does not then it's a failed EL34...

    -Jon
     
  10. Greazygeo

    Greazygeo Member

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    But they sound terrible? Anything else?
     
  11. VintageJon

    VintageJon Member

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    "But they sound terrible" HUH? They sound great and live long here! Huh???

    Now, where you get them from, how you test them, and how you ship them are critical.

    Here it's CE, shipped USPS, tested on Hickok 800,match tested on a Twin Reverb converted to Tube Tester for Cathode Current Test, burned-in for 60 minutes at max clean output, tested again for Cathode current.

    Testing is everything in componets. You have to take the time and charge for for it. It was always thus...

    Cheers,
    Jon
     
  12. Greazygeo

    Greazygeo Member

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    I did rebuild the bias circuit ( has a bias adjuster pot now) and the filter supply. I've got it biased about 32 ma right now. It runs just fine with the Svet's until the vol goes up over half, then the mains fuse pops. With the old Mullard's I can crank it all afternoon with no problems...

    It sounds great too :AOK

    http://greazyspoon.net/clips/Flight.mp3

    I guess I could try two of the Svet's instead of 4....see how that is. Ive got some EH's here too, I dont think those would be good in this amp though...
     
  13. Greazygeo

    Greazygeo Member

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    Hey Jon,

    Thanks for the info. Over the years Ive tried most of the JJ tubes and just don't like their tone. They have this upper mid harshness that I don't like and the preamp tubes sound flat and dull. The EL34's have too much of a *hard* edge to them and the upper mid thing I don't like. It was the same with the Tesla's....I do like them in hi-fi stuff though. They sounded great in my old MC40! In my Marshalls, Wizard's and VHT, not so good.....
     
  14. Swarty

    Swarty Member

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    Not necessarilly a failed EL34. An arcing socket can/will blow a mains fuse, and only if there is a tube in it.
     
  15. John Phillips

    John Phillips Member

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    Strange nonetheless that it blows the mains fuse and not the HT - assuming you have the right values for both!

    Where are you? (ie, what supply voltage are you running at?) If you have the 240V fuse value in the mains and are running on 110-120, it will blow when the amp is putting out a lot of power no matter what tubes you have in, simply because the current demand is greater. But with only two tubes in it likely won't blow since the maximum power draw is roughly halved, which brings you back down below the fuse rating for double the supply voltage...

    I could be wrong of course, but check that first. From memory the HT should be 1A and the mains 3A at 240V but 5A at 110V.

    I would also bias it cooler than that, if you can. 70% is too hot for amps like this that can develop more than the tubes can really handle, you need to be in the 50-60% region ideally.
     
  16. Greazygeo

    Greazygeo Member

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    1 amp and 3 amp is correct and is what is in there...Im in USA running 120VAC. The selector is set on 115V, so I don't doubt the amp is running harder than it would be at 115V. I've thought about getting a variac and setting it at 115V and see how it is.
    The bias supply is adjustable and I had it at 28, 30 and 32ma. It sounds best (to me) at 32ma with these tubes. I dont mind lowering it alittle, but it really doesnt seem to be running hot.

    It seems most times I hear of old Orange amps having troubles is running newer tubes. This amp has never given me any trouble with the Mullard's....I just don't really want to have to fork out the bucks for them now, but it might come to that :mad:
     
  17. John Phillips

    John Phillips Member

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    That's exactly what I thought. 3A is the correct fuse value for 240V. For 120V you're going to need more - that amp will probably draw around 375-400W at full power, which is about 3.1 to 3.5A at 120V, so it's not surprising a 3A fuse is blowing. If you have any doubts about this, measure the AC current input to the amp while cranking it with all four tubes in. You need the lowest fuse value (slo-blo) above the peak current demand the amp requires.

    It won't at idle, but watch what happens when you crank it. If you measure the tube dissipation at full power, you may well find it's well over the rated tube power. Mullards will take it, but many modern types won't.

    I would. I don't think they're poor value for money even now, since they're far more reliable, long-lasting and better-sounding than any new-production tubes.
     
  18. scottosan

    scottosan Supporting Member

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    Thats a great point. Double the voltage equals half the amps. 100 watt Marshalls are 2A and 1/2 amp in the UK, but 4 amp and 1 amp in the US. I guarantee that amp needs more than a 3A fuse running 110v
     
  19. VintageJon

    VintageJon Member

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    Swarty and John Phillips- good points! Damn fine....

    -Jon
     
  20. Greazygeo

    Greazygeo Member

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    So you think a 4 amp would work ok? I think I have 4 and 5 amp fuses around here....then I might try those Svet's again and save my Mullards for recording...unless they just sound bad!

    I did find some quads of GE 6CA7's for not too bad a price, I always liked those in my old '72 50 watt (till I found some Mullard KT88's that is :D). I have not found any quads of Mullards, just lots of pairs.
     

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