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Thread: tube swap

  1. #1
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    tube swap

    Can i use 6v6gt tubes in my pignose G40v instead of the 6l6's ?

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    Hi baddog: If your G40v is rated at much more than 15 watts, probably not. The pinouts are the same but the power handling isn't. You can safely put 6L6s in a 6V6 amp but not necessarily the other way around. CJ

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    6v6 swap

    Thanks for the info i guess i will save them for an amp build when i can afford it. Thanks to everyone for everthing

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    I have the G40V schematic and it shows 406v on the 6L6 plates. A set of 6V6s should stand up to that with no problem. Deluxe Reverbs run them around 420v if I recall.

    Aside from the usual checks like proper bias voltage, I don't see why you couldn't pop a set 6V6s in your Piggy.

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    "You can safely put 6L6s in a 6V6 amp but not necessarily the other way around"

    That is not accurate.

    A 6V6 push/pull amp may have a PT of around 90ma capability (such as a Princeton Reverb or old Silvertone 1482) with 6L6 amp having a PT of around 140ma.
    6L6's in a 6V6 amp may toast the "6V6" PT by drawing 140ma current with the PT only being capable of handling 90ma.

    However, if the voltages to the 6L6 plates are within 6V6 tolerances (such as the JJ 6V6"s) then you can put 6V6's into a 6L6 amp. JJ 6V6's are reportedly rated by manufacturer to 500v.

    With respect, Tubenit

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    Senior Member capnjuan's Avatar
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    Hi baddog: see what you get for asking a simple question? I took your question to be a practical one and not necessarily an electronic hypothetical. I probably also assumed that since you were asking the question in the manner that you did, that you might also find the idea of adjusting whatever type of bias you have Ö challenging. So, I confess that it was my intention to discourage you from the beginning. I donít know your amp but these remarks assume itís a Class A/B1 Push Pull design Ö and I have no idea of whether itís fixed- or cathode-biased Ė and, nothing personal, I donít really care.

    This is a link to Duncan Ampís Tube Data Sheet Locator http://tdsl.duncanamps.com/show.php?des=6V6 For any of the 6V6 types listed, youíll want to page down to the section that says A/B1 PP and read in the column Va and Vg2; these represent the general design criteria for voltage limits on the 6V6 plates and screens. For the listed variants of 6V6 tubes, in no case is there a recommended operating voltage on the plates in excess of 285 volts.

    If, as citizencain suggests, the plate voltage in your amp is in excess of 400 volts, then putting 6V6s in your Pignose would put the 6V6s at risk. Itís true; there are successful, good-sounding amps that operate 6V6s well in excess of their conventional ratings but I note that the suggestion that itís okay to do so comes from someone whoís gear isnít at risk. Oh yes and by the way, youíd have to work out the necessary changes to the bias too. Again, I assumed you were talking about a simple swap; not re-engineering parts of the amp.

    As tubenit pointed out, the new JJ Tesla 6V6s here, http://www.jj-electronic.com/pdf/6V6.pdf are rated to 500 volts but for Class A1 operation, not Class A/B Push Pull. For a discussion of amp design and operating classes http://www.aikenamps.com/ClassA.htm On the subject of 6L6s into a 6V6 amp, here are two links for your reading pleasure: http://www.tdpri.com/forum/archive/i...p/t-52593.html and http://www.thegearpage.net/board/sho...d.php?t=317598. In short it depends on the amp and to what degree youíre willing to change a 6V6 amp to accommodate 6L6s. Tubenit is right though about the current draw; the 6L6 draws more current than a 6V6; I was a little quick on that one.

    Not that you asked but if you want a 6V6 amp, go find a beater Kalamazoo, Silvertone, Gibson whatever and rehab it. Best wishes and good luck with your amp.

    John

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    tube swap

    Thanks for all of the input its greatly apreciated

    baddog

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    What are you up for?

    The amp is fixed bias, and you can't just change to 6V6s without adjusting the bias with a pot that the amp doesn't have yet, but would benefit from anyway.

    An amp tech can host 6V6s in that amp for probably around $60 if you supply the tubes and a few simple instructions. Swapping R3 and R4 will drop the plate voltage, and using the 4 Ohm output with an 8 Ohm load will compensate for the low output transformer impedance. The main thing you need, which may be beyond your capabilities (you'd want a bias probe), is a bias pot installed, and a possible change to the low-value HV cap that sources the negative voltage to the bias circuit. Otherwise, it's likely the power tubes will melt down, or better, sound awful.

    Once its done, the loading on the cheesy power and output transformers will be reduced, and the tubes will be operating at the proper operating point. You still won't have reverb.

    Be careful in there. There's a surprisingly large number of surprisingly large value caps with 400V on them, that will store charge for a long time after you unplug the amp.

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    Quote Originally Posted by BackwardsBoB View Post
    The amp is fixed bias, and you can't just change to 6V6s without adjusting the bias with a pot that the amp doesn't have yet, but would benefit from anyway.

    An amp tech can host 6V6s in that amp for probably around $60 if you supply the tubes and a few simple instructions. Swapping R3 and R4 will drop the plate voltage, and using the 4 Ohm output with an 8 Ohm load will compensate for the low output transformer impedance. The main thing you need, which may be beyond your capabilities (you'd want a bias probe), is a bias pot installed, and a possible change to the low-value HV cap that sources the negative voltage to the bias circuit. Otherwise, it's likely the power tubes will melt down, or better, sound awful.

    Once its done, the loading on the cheesy power and output transformers will be reduced, and the tubes will be operating at the proper operating point. You still won't have reverb.

    Be careful in there. There's a surprisingly large number of surprisingly large value caps with 400V on them, that will store charge for a long time after you unplug the amp.


    planning on installing a bias pot with taps so I can try 6v6's. If Leo can run a deluxe with over 400vdc on the plates I thin I'll give it a try. I also installed an organ output transformer with a 5k primary and 8 ohm secondary. I'm going to see if I can set it up to run 6v6's or 6l6's.

    Thanks
    Baddog

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    I replaced the 68k resistor to ground with a 25kl pot and 39k resistor. I have enough voltage swing to run either tube set. Works great. With 6v6's I have about 420vdc on the plates @ 22mv bias. With 6l6's I have 404vdc @ 44mv bias.

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    Well done.
    I was thinking that you've taken a while to get around to this, but then I remembered all the projects I've got on the back burner, some for decades!

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    Well it wasn't really a back burner thing, I just didn't know enough at the time to do the mods. The amp had been sitting for a few years while I was getting better at the art of amp building and modding. I turned a Bassman into a Robben ford dumble clone, built a nice TMB 18 watt clone and did a few other things in the time I original posted the question.
    I have a couple more changes to make to the old pignose bit it's a pretty good amp the way it sits. I originally made it into a head unit but I think I'm going to put it back into its cab. I did make the cab a 1x12 and I think I'll keep it that way.
    It's cool to see someone is still watching of even remembers this thread. Thanks for caring and replying.

    Keith

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    The 6l6's sound pretty good as you'd expect. Nice full tone with good smooth highs, and with enough gain to Gary Moore happy. The 6v6's are more focused on a tighter tone with more highs. Not as full as the 6l6's but pretty darn good sounding in there own right. Tighter bass with more focus on the highs. I have been playing this in an unfinished basement on my work bench so I can't really get a good feel on the true tone of the amp. I usually take my amps out on the back deck and try them out at volume but seeing as it's fall and getting cold oh it's a little harder to do. I'll have to make do and see what I can do to test this thing some more. Il keep you guys posted if you like.

    Thanks
    Keith

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    Maybe a 16ohm speaker with the 6v6's... Hmm

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    Ordered a new 20kl 10 turn 2watt potentiometer. Should be nice for adjusting the bias more accurately and its a 2 watt unit. I'm also adding taps for the bias alias and plate voltage so I can swap tubes without removing the chassis from the cab. I might also add a standby switch if I have the extra parts.

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    crappy picture of the back but:





    Running a matched pair of these


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    Quote Originally Posted by BackwardsBoB View Post
    The amp is fixed bias, and you can't just change to 6V6s without adjusting the bias with a pot that the amp doesn't have yet, but would benefit from anyway.
    This is misleading. Fixed bias means it does have an adjustable bias pot (so you can 'fix' the bias). If it does not have a bias pot it is cathode biased.

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    It's weird, because it WAS working fine.....

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    Also not entirely right... lots of amps don't come with a pot yet are fixed bias. Peaveys & Mesas come to mind, and Princeton Reverbs... Also, all those SF Fenders with the bias balance. Fixed bias means a constant negative voltage is applied directly to the grid and the cathode is grounded. A better term for amps with a bias adjustment pot would be "adjustable fixed bias."

    Justin

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    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
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    Well done.

    Caution on a post above saying you can safely put 6L6 in a 6V6 Amp (opposite of what you have done). In a some cases this 6L6 in place of 6V6 will cause grief due to MUCH higher heater current requirements.

    Cheers,
    Ian

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