6L6G users?

Discussion in 'Amps and Cabs' started by Reg18, Feb 26, 2015.

  1. Reg18

    Reg18 Member

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    I have just picked up an old USA Tung Sol 6L6G (haven't had time to try it yet)
    Can't find much on the net in regards to this tube, I will be putting it in a VHT Special 6 Ultra combo. Currently running a Slyvania 6V6 in the amp but keen to try some other tubes to see how they sound.

    Anyone had experience with 6L6G tubes? Can you explain how they sound compared to a 6L6GC?
    I assume the old USA Tung Sol should be pretty decent based on their reputation but who knows....old tubes are a bit of a gamble!
     
  2. swiveltung

    swiveltung Member

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    Lower output predecessor to the GC.
    BTW: your output transformer will be different output impedance switching the 6V6 to a 6L6.
    If 8 ohm with the 6V6 will be 4 ohm with the 6L6.
     
  3. Reg18

    Reg18 Member

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    I didn't know this, VHT say in the manual that you can experiment with different power tubes but don't say you need to change the impedance.

    Can anyone look at this schematic and tell me if this is the case?

    http://www.vhtamp.com/images/Manuals/vht special 6 ultra manual.pdf
     
  4. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I've used lower-output 6L6G in tweed-ish amps, such as my Richter 5E7+, early Valco-like Vintage 47 Bronson, and in my dual single-ended Victoria Regal II. You want to be sure you don't fry them in a circuit designed for higher voltage 6L6GC.

    I happen to prefer 6L6G sound, in general, over any 6L6GC (including RCA and GE). But they're more delicate and have lower output. The sonic character of 6L6G vary such that I couldn't generalize about all 6L6G compared to all 6L6GC. I happen to enjoy Ken-Rad 6L6G, and find them to have the best clarity of all I've tried - including original Tung-Sol 6L6G, which are also very good.

    If your amp can run 6L6G, then it can also use 6L6GA, 6L6GB, 6L6GT, 5881 and 5932 and maybe even EL37.

    - Thom
     
  5. swiveltung

    swiveltung Member

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    It's a function of the Output Transformer. It looks like your amp is 16 ohm output normally?
    If so then probably switch the impedance switch on the back to 8 ohm for the 6L6.
    Does your manual say you can use a 6L6? Is it self biasing?
     
  6. Reg18

    Reg18 Member

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    Yes it is stated you can experiment with different tubes including 6L6, EL34 etc
    I don't really see how changing the output tubes changes the ohms at all.
    Can someone explain this to me?
     
  7. CubanB

    CubanB Member

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    I can attempt to answer but hopefully someone more experienced can shed light on it for you. As I am still learning myself.

    To understand the reason why, requires an understanding of the difference between primary and secondary wirings of transformers, the ratio between them and how different tube types require a different impedance for optimum performance.

    For EL34/6L6, they can be interchanged without changing primary impedence but performance will suffer. When using 2 tubes, you want..

    3.2-3.4K primary impedance for EL34
    4K-4.2K for 6L6
    8K for 6V6
    6.6K (I think) for EL84

    EL84 or 6V6 require a higher impedence of 6K or 8K, but memory is fuzzy as I haven't used them before.

    The primary impedance for the tube is important, not just for tube type but also total number of tubes, when using 4 tubes instead of two, everything halves. So 2K for 4 6L6's or 1.6L for 4 EL34's.

    Changing the output transformer is a labour intensive and expensive endeavour, but you can interchange them by using different secondary windings (4 ohm, 8 ohm etc), so that the tube sees the primary impedance on the primary side. Intentionally causing an impedance mismatch.

    So that you can use an output transformer that is intended for a higher or lower wattage output, or for a different spec of tubes, but keeping the tubes happy by making sure the tubes see the same impedance on the primary side. 6V6, just so happens to be double of 6L6's primary impedance, so by running an intentional mismatch on the speaker side, you can give the tube the impedance it wants to see. By halving or doubling it depending on which direction you go.

    You can see by the numbers above that it'd work better with EL34s and EL84's, and 6L6's and 6V6's.. rather than other combinations.

    There are other complications to different tube types, like the current drawn from the screens (pin 4), or the max voltage the screens can handle or the max plate voltages they can take (pin 3) depending on what that type type can handle. These two things combined with the output transformer are the main reasons which make it harder to have ALL types of tubes optimised for one amp. It's usually better to optimise it for one or the other, because while it may function with other tubes, it won't sound optimal.

    I'm not familiar with 6L6G but it sounds like in the case of using them, you'd want to make sure plate and screen voltage aren't as high as it would be for 6L6GC. The tube datasheets show the max they can handle and some brands of the same spec of tube can vary. So JJ's might be able to handle more voltage than Electro Harmonix, for example.

    I'm not sure I explained it 100% clearly, but it's all about the ratio of primary vs secondary impedance of the transformer. And intentionally halving or doubling it so that it can match what the tube wants to see.

    The primary carries the high voltage to the plates of the tubes and different types of tubes like to see a different impedance or load (4K in the case of a 50W 6L6 amp). It goes through the output transformer into the secondary side, and comes out as a low voltage high current AC signal.. which is what the speaker wants to see.

    By playing around with ratio of the speaker impedance, you can manipulate the load that the tubes see on the primary side without having the change the transformer itself.
     
  8. heisthl

    heisthl Member

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    This is backwards, if you have a choice of output impedances in a 6V6 amp you want the next number higher with 6L6. In a 6L6 amp you choose one number lower when you try 6V6.
     
  9. swiveltung

    swiveltung Member

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    Yes, I may have stated that poorly.
    Maybe this is better:
    an amp that normally has 6V6 power tubes at 8 ohms output, will match 4 ohms output with 6L6 power tubes.
    If I remember correctly... that amp the OP has ....it has a multitap Output Transformer.
    However it has a 16 ohm speaker ( I think!)
    Even with the multitap Output tranny he will never be able to match the 16 ohm speaker with a 6L6. ... right?
    However, it might be fine for home playing... worth a try maybe...
     
  10. Blue Strat

    Blue Strat Member

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    Without writing an essay which has more information than anyone needs to know (for this example), every active electronic device, including tubes, as an inherent impedance...and they vary from one device to the next. Such is the case for 6V6s and 6L6s. 6V6s have about double the output impedance of 6L6s.
     
  11. heisthl

    heisthl Member

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    I know this is confusing, go the the Aiken site to read up on output transformer impedance (http://www.aikenamps.com/index.php/output-transformers-explained) and when you first read this you might think it goes in the other direction:
    If you put 1VAC across the secondary, and measure 20VAC across the primary, you have a turns ratio of 20:1, which corresponds to an impedance ratio of 400:1. This means that if you put an 8 ohm load across the secondary, you will get a reflected impedance of 3.2K ohms across the primary. If you put a 4 ohm load across the secondary, you will get a reflected load of 1.6K ohms.
    But the key here is he's talking about reflected load within the transformer in an output to input direction - not about the tube's impedance changing so you need to take it one step further and think about what happens when the only change is the tube's impedance. Using his numbers to make it easy assume 3.2k for 6V6 tubes and 1.6k for the 6L6 tubes.
    If your target impedance is an 8 ohm speaker no problem with 6v6 in his example but when you install 6L6 bear in mind the transformer is going to reflect that change on it's output - the speaker can't magically change to 4 ohm but we can pick a different output tap to compensate (the correct tap to choose would now be the 16 ohm tap). So yes, if he has a 16 ohm speaker he would need a 32 ohm tap to use the same speaker with 6L6. Best to just change the speaker to an 8 ohm. Hope this helps - HH
     
  12. Reg18

    Reg18 Member

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    I emailed VHT about this issue, this is there reply:
    Hi Reg,

    No worries, you can install any of those tubes without any problems.

    When trying these larger tubes, to be the most theoretically correct, you should set the impedance selector to twice the actual speaker impedance.

    But it's not as crucial as some people might have you believe, you can also use the same impedance setting without any problems (for example, you can use the 16 ohm impedance selector setting with a 16 ohm speaker).

    Hope this helps, please feel free to experiment, thanks for contacting VHT Customer Support
     
  13. CubanB

    CubanB Member

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    There's videos online of Soldano modding amp to use EL34 instead of 6L6 and talking about the differences of using different tubes with the same amp. You can switch them some types (generally speaking) and they might function but won't sound optimal unless certain factors are in place. The impedance is one of them, as has been discussed here.

    Best to judge by your own preference and ears I guess, since you know that with that amp both options are safe and will function.
     
  14. Blue Strat

    Blue Strat Member

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    Yes, because most amps will withstand a 2:1 or 1:2 impedance mismatch with no issues except lower power output.
     

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