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Thread: 6BM8 tubes... what to use them for!

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    6BM8 tubes... what to use them for!

    Has anyone used many of these 6BM8 tubes?
    I have a great idea for a tiny, three tube, 10-12 watt, push pull amp using these.
    I have a bunch of vintage 1980s, Svetlana 6BM8s and except for an old Hi-Fi audio amp, I've never used them for anything else.
    Bruce

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    Member Chuck_Farlee's Avatar
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    Quote Originally Posted by Bruce / Mission Amps View Post
    Has anyone used many of these 6BM8 tubes?
    I have a great idea for a tiny, three tube, 10-12 watt, push pull amp using these.
    I have a bunch of vintage 1980s, Svetlana 6BM8s and except for an old Hi-Fi audio amp, I've never used them for anything else.
    Here are a couple of schematics:

    http://www.schematicheaven.com/barga...estminster.pdf

    http://www.schematicheaven.com/barga...inster_10w.pdf

    Here's a 6GW8 amp from Paul Ruby, who posted it on the AX84.com BBS:

    http://paulrubyamps.com/6gw8.html

    It would probably be easy to mod to use the 6BM8.

    chuck

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    Hi Bruce,

    here is a nifty German design from the Fifties.
    TA means Tonabnehmer (pickup / record player). The mic channel has a "pull boost" function and TA1 a "pull fat" (not named like that of course).
    The tone control with "pull mid scoop" is incorporated in the NFB loop.

    Oh yes, and "KV10" means "Kofferverstärker 10W" (suitcase amp 10W). You could add a second speaker cabinet and amplify literally everything.
    After all, 10W is plenty for EVERY party, isn't it?

    Cheers,
    Albert
    Attached Thumbnails Attached Thumbnails kv10_sch.gif  

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Thanks. Great ideas and I like all of those examples.
    My idea is a little different but still along the same lines, especially with respect to using the 6BM8's triode as part of the phase inverter.
    I ran into a boatload of $25.00 power trannys that will make about 340vdc@100ma with a choke input filter and FWB SS rectifier.
    That PT and a little $30.00, 12 watt Princeton Reverb sized OT out to make a great foundation for a little pocket rocket.
    Any other ideas are more then welcome because when I'm done, this will be a community project amp.
    Bruce

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    I saw an article online (possibly by Eric Barbour when he was with Svetlana), that used the 6BM8 as a reverb driver in Fenders.

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    http://www.aronnelson.com/gallery/ma...TenWattWonder/

    Sound clips are great, very much like an AC15, and Doug has made some great little amps. Is this close to what you had in mind, Bruce?
    Last edited by Ben N; 04-25-2008 at 05:25 PM. Reason: clarify

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    You may want to check out these threads:
    http://www.el34world.com/Forum/yabb2...num=1195825729
    http://www.el34world.com/Forum/yabb2...num=1163435923
    http://www.el34world.com/Forum/yabb2...num=1194702099

    The Mini-Bassman sounds really good. I'm still gathering up parts to build one up, and I think it put out somewhere around 10watts.

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by JoeM View Post
    I saw an article online (possibly by Eric Barbour when he was with Svetlana), that used the 6BM8 as a reverb driver in Fenders.
    Yes I have that schem... good one.
    Bruce

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by Ben N View Post
    http://www.aronnelson.com/gallery/ma...TenWattWonder/

    Sound clips are great, very much like an AC15, and Doug has made some great little amps. Is this close to what you had in mind, Bruce?
    That's pretty cool... a little too much low power buzzy distortion for me but on the right track for what I am planning.
    I want a little more clean to mean control...
    Bruce

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by echuta13 View Post
    You may want to check out these threads:
    http://www.el34world.com/Forum/yabb2...num=1195825729
    http://www.el34world.com/Forum/yabb2...num=1163435923
    http://www.el34world.com/Forum/yabb2...num=1194702099

    The Mini-Bassman sounds really good. I'm still gathering up parts to build one up, and I think it put out somewhere around 10watts.
    Great stuff there... thanks for those.
    Yes, that is what I think I am leaning towards.... a 10watt, low power, tweed Bassman/VOX AC30 type sound but with a simple master volume control so that it can be driven into "high gain "Marshall" tone.
    I want to be able to roll the guitar volume down a bit to get back a cleanish VOXY tone meets tweed Bassman mix and then just crank the guitar volume up to get the overdrive.
    And all with only three tubes... I have it drawn out (I'm sure it will work) and have a tiny 10" chassis with a small PT, an OT from a Princeton Reverb (8K), a semi-large lunch box sized finished head cabinet, and I'm getting close to being ready for the experiment.
    I just want to see what others have done with these 6BM8s so I don't have to repeat too many mistakes from the start! ha ha
    Bruce

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    I know I haven't been on this forum long (I was on ampage 10 years ago but I guess that doesn't count) but this sounds like a fun idea. I have a few Princeton sized outputs, some 6BM8's and a few similar PT's so I'd love to see what people come up with.

    I was just thinking earlier today of building a bedroom/church gig amp with a Trainwreck style SE amp with a 6BM8. I was thinking a 12ax7 would form the first two preamp stages then the triode in the 6bm8 would form the final preamp stage, followed by a master volume driving the pentode's grid. It wouldn't be very loud but I bet the preamp would have more than enough drive to punish the pentode. I'd probably use a split load off of the preamp if it was too much for the output tube.

    The reason I mention it is I had the same idea in mind- something that would be pretty dirty but clean up and sound pretty with the volume knob.

    jamie

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    Member sportster4eva's Avatar
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    They seem to have an el84 quality to them. Try to keep your B+ somewhere around 300v, not sure how they would handle much more.
    I have an old Univox U-45B that uses them. The thing really screams when cranked. Nice little tubes. Great little amp after a cap job. The OPT is 10k impedance.

    Bruce, any chance you'd consider parting with a pair?
    Last edited by sportster4eva; 04-27-2008 at 10:53 PM. Reason: I remembered something
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    Supporting Member tubeswell's Avatar
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    Found a circuit for ECL86 (not ECL82)

    http://www.r-type.org/static/ecl86.htm

    Don't know it its much help

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by sportster4eva View Post
    They seem to have an el84 quality to them. Try to keep your B+ somewhere around 300v, not sure how they would handle much more.
    I have an old Univox U-45B that uses them. The thing really screams when cranked. Nice little tubes. Great little amp after a cap job. The OPT is 10k impedance.

    Bruce, any chance you'd consider parting with a pair?
    Sure.
    I had a U-45B for a while and I found that also replacing every single coupling cap on the PCB (mine had these sickly, sea foam, puke green caps) with inexpensive Xicon MPP 630v caps made a huge difference in the way that thing sounded! Mine might have been a little ill at first but it was pretty impressive for a $25.00 garage sale amp.
    It really ripped driving a 2x10 cabinet with a pair of well worn in C10Qs.

    The little PT I'm going to try and use will have the B+ rail at around 350vdc with a choke input filter... it looks like the tube can easily handle that so it will just be a matter of tweaking it.
    ***************************
    With the U-45B amp rockin' out, please tell me what the AC voltage is across the two pentode's grids... in other words, how much audio voltage is the PI hitting the grids with?
    That is really what I'm looking for with respect to how much gain tweaking my little circuit is going to need.
    I have this crazy idea to make a baby, three tube, 10 watt, AC30'ish/Bassman/Plexi thing.
    Last edited by Bruce / Mission Amps; 05-01-2008 at 10:04 AM. Reason: new thought added...
    Bruce

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by tubeswell View Post
    http://www.r-type.org/static/ecl86.htm

    Don't know it its much help
    Yes that is helpful... in most applications, the EF86 makes about the same gain as two 12AX7 triode in series.
    Well, it has a mu of around 5000 and the 12AX7 triode is 100 x's the other one of 100 or 10,000... neither will really approach that so I say they are about the same in circuit.
    I still want my little amp to have three tubes total but it isn't because I want the huge amount of gain.
    Bruce

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    Supporting Member tubeswell's Avatar
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    Quote Originally Posted by sportster4eva View Post
    any chance you'd consider parting with a pair?
    FWIW Svetlana and EH are making new production ones
    Attached Thumbnails Attached Thumbnails 6bm8svet1996.pdf  

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    Quote Originally Posted by tubeswell View Post
    FWIW Svetlana and EH are making new production ones
    Rebranded russian 6F3P, an approximative substitute for ECL82/6BM8. Triode section is pretty close to the original but the pentode is not, especially if you want to maximize output power. Original NOS ECL82 are easy to get and if you can raise heater voltage to 16V try PCL82, even easier to find.
    Aleksander Niemand
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    I have built a handfull of 6BM8 amps. They allow a very compact build. The first one that I made was a copy of a Gibson amp that used that tube. I was able to construct it using a 5"x7" chassis. A few of the amps went into old wall hanger speaker boxes I found at hamfests, old space heaters, and the like. With the current popularity of low power amps, I was surprised that more people didn't use them. As far as I know the current product is made in St. Petersburg. Russia.

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    Quote Originally Posted by Bruce / Mission Amps View Post
    With the U-45B amp rockin' out, please tell me what the AC voltage is across the two pentode's grids... in other words, how much audio voltage is the PI hitting the grids with?
    That is really what I'm looking for with respect to how much gain tweaking my little circuit is going to need.
    I have this crazy idea to make a baby, three tube, 10 watt, AC30'ish/Bassman/Plexi thing.
    Marshall/5f6a non-mv pre with only one channel so only 3 triodes are used, single tube phase splitter into the 6bm8 outputs?

    Or skip the cathode follower so you have an extra gain stage or a LTPI?

    There's always the mosfet cathode follower option...

    jamie

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by imaradiostar View Post
    There's always the mosfet cathode follower option...

    jamie
    That's the one I'm leaning to. My only concern is too much gain for these little 6BM8 bottles... I've already built that circuit a number of times with 6V6s and it works perfectly but the pre is hot for sensitive grid tubes.
    So yeah, the other thing would be to use a cathodyne driver instead of the +gain LTP driver and the left over triode for the cathode follower.
    I have not mocked that one up yet.
    ****
    I just though of another way to do it by using a voltage divider bias for a cathode follower and only use the second triode to drive the CF.
    I'd put a volume pot between them and a coupling cap to keep DC of the pot.
    Then the two triodes of the 6Bm8 would be TONE control recovery/amplification/PI driver into the other triode, the cathodyne driver.
    I guess I should stop typing and think it out more 'cause I just though of a third circuit.
    Last edited by Bruce / Mission Amps; 05-02-2008 at 06:41 AM. Reason: added a thought... then another
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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by Alex/Tubewonder View Post
    Rebranded russian 6F3P, an approximative substitute for ECL82/6BM8. Triode section is pretty close to the original but the pentode is not, especially if you want to maximize output power. Original NOS ECL82 are easy to get and if you can raise heater voltage to 16V try PCL82, even easier to find.
    Thanks Alex... do you know what the "real" power dissipation rating or out put of the pentode side is in these.... they are super cheap. I have the Svetlana versions.
    I'm really not looking for EL84 output power... I want this to be a little bottle rocket with a nice report.
    Bruce

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    Member Le Basseur's Avatar
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    There's also another possible use for the ECL82/6BM8 tube.
    I remember that Audio Note (High-End brand) uses this tube in some of their most expensive preamps (M-something) in the HV power supply,as a regulator.Also,in the same circuit,they use a voltage-stabilizing tube such as OA2,OB2,etc. as a voltage reference.I have somwhere this schemo,if anyone's interested.
    All I can say about this "offstream" use of the ECL82/6BM8 is that makes every difference in the world when dealing with small signal circuits (RIAA,line preamps and such...when I'll get some more time,I intend to build this particular PS and hook it to a guitar preamp...ANY guitar preamp).AFAIK,Andy Grove,the AN's "tech brain", gave his best when made the circuit's fine tuning.
    Regards,

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by J Martin View Post
    I have built a handfull of 6BM8 amps. They allow a very compact build. The first one that I made was a copy of a Gibson amp that used that tube. I was able to construct it using a 5"x7" chassis. A few of the amps went into old wall hanger speaker boxes I found at hamfests, old space heaters, and the like. With the current popularity of low power amps, I was surprised that more people didn't use them. As far as I know the current product is made in St. Petersburg. Russia.
    Senor Martin, I love that idea... I'm really in the mood to do something fun again.
    A friend of mine has a little one or two watt 6AQ5 amp in an old 60's, chrome Sunbeam toaster and although it has a tiny 3" speaker in it, which sounds dumb, it does have a speaker jack and it sounds good into a little aux cabinet he made from a small, blown up hi-fi shelf speaker.... just fun stuff for a change.
    Anyhow, I was finding these really old junk shortwave radios on Ebay that would be perfect for a nutty, table top, rippin', 7-10 watt guitar amp and thought it would be fun to house them in an old gronky thing like these:
    http://i14.ebayimg.com/01/i/000/ec/71/f5d7_1.JPG
    http://imagehost.vendio.com/bin/imag...n/DCP_3584.JPG
    http://www.baltimorejohn.com/images/DSCN0075.JPG

    Look at this that sold for $21 and has an 8" or 10" speaker in it.
    http://i12.ebayimg.com/07/i/000/eb/e4/0603_1.JPG

    Of course you'd have to clean them up....

    But I have even a better idea and when I get it mocked up I will reveal it to you all for a really killer little lunch box size toy that will be a rockin' dog too.
    Bruce

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    Quote Originally Posted by Bruce / Mission Amps View Post
    Thanks Alex... do you know what the "real" power dissipation rating or out put of the pentode side is in these.... they are super cheap. I have the Svetlana versions.
    I'm really not looking for EL84 output power... I want this to be a little bottle rocket with a nice report.
    Bruce, RFDS it's all here

    You can get ca 3.5W out in SE, up to 10W in AB PP with 270V B+
    Pentode max Pa=7W, triode 1W.
    Aleksander Niemand
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    Mini-Bassman sound clips

    Bruce,

    Check out the clips of the 6BM8 that DaGeezer did with the mini-Bassman which he now calls the Little Wing.

    http://www.musicwebtown.com/jallenshaw/46763

    I built one of these with reverb and it's the most expressive amp I have ever played since I picked up guitar in '65.

    http://s28.photobucket.com/albums/c2...rbcombopic.jpg
    http://s28.photobucket.com/albums/c2...reverbtank.jpg
    http://s28.photobucket.com/albums/c2...srearpanel.jpg
    http://s28.photobucket.com/albums/c2...terirofron.jpg

    The 6BM8 concept amps schematics are ones I drew up and I haven't built them. Just posted the ideas for others.

    I don't hear a similarity with EL84's and 6BM8's and I have owned amps of both. I think the 6BM8 is a warmer and smoother sounding tube, IMO.

    With respect, Tubenit

  26. #26
    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by Alex/Tubewonder View Post
    Bruce, RFDS it's all here

    You can get ca 3.5W out in SE, up to 10W in AB PP with 270V B+
    Pentode max Pa=7W, triode 1W.
    Thanks Alex.... I had already download a fair amount of info regarding these 6BM8 tubes but you alluded that the Russian ones don't have a pentode side that is comparable to the NOS ones.... that's why I mentioned that the pile of 6BM8s I have are old NOS Svetlana tubes, which of course, is a Russian tube! ha ha....
    So, were you saying that the Russian (Svetlana) tubes are also defective in some way or the Russian pentode does not have a dissipation rating as real NOS 6BM8s?
    Bruce

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  27. #27
    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by Tubenit View Post
    Bruce,

    Check out the clips of the 6BM8 that DaGeezer did with the mini-Bassman which he now calls the Little Wing.

    http://www.musicwebtown.com/jallenshaw/46763...


    I don't hear a similarity with EL84's and 6BM8's and I have owned amps of both. I think the 6BM8 is a warmer and smoother sounding tube, IMO.

    With respect, Tubenit
    Great info!... the little wing version, with out reverb, is exactly where I'm heading with this 6BM8 project.
    I've mocked it up with 6V6s in a 5E3 chassis and it works GREAT with the extra 12AX7 (actually I found a 12AY7 still sounds better).
    My main concern is that will the 12AX7s have enough gain to smash the 6BM8 Pentodes so I have to see what can be done about this part.
    Bruce

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    Here is the original russian data sheet for 6F3P, also in english. Pentode Pa is quoted as 8W.

    It's close for most purposes and you can use 6BM8 recommended Ra loads.(8k @ 270V) However, if you really want to squeeze the most juice out of it you better get your ruler and pencil and draw load lines. There will be differences in distortion characteristics between western and soviet version.
    If you look at plate curves on Tungsol or Mazda Bellevue datasheet you will see that it has a pronounced kink typical of tetrodes whereas the russians show true kinkless pentode behaviour. At the same time Svetlana data sheet shows curves with the kink....(question: whom do you believe?)

    I guess you'll need to do a comparative test and tweak the circuit to make the Svetas sound as originals or vice-versa

    Have fun, good luck. I'm curious about what you'll come up with.
    Aleksander Niemand
    Zagray! amp- PG review Aug 2011
    Without the freedom to criticize, there is no true praise. -Pierre Beaumarchais, playwright (1732-1799)

  29. #29
    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by Alex/Tubewonder View Post
    Here is the original russian data sheet for 6F3P, also in english. Pentode Pa is quoted as 8W.

    It's close for most purposes ....

    I guess you'll need to do a comparative test and tweak the circuit to make the Svetas sound as originals or vice-versa

    Have fun, good luck. I'm curious about what you'll come up with.
    OK I looked that over and I see what you mean.... so, Yup... I think a mock up is the key here.
    I really wanted to use all these $25 PTs I have here, which will end up making around 350vdc (even with a choke input filter) and the inexpensive reissue 8K Princeton Reverb OTs.
    I just had a thought... I guess a guy could use this Weber PT:
    https://taweber.powweb.com/store/wrvbptsch.jpg and wire it to the 125v tap.
    But I'd have to buy those! ha ha
    Bruce

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    Little Wing 6BM8 amp

    " My main concern is that will the 12AX7s have enough gain to smash the 6BM8 Pentodes"


    Are you going to drive the 6BM8's pentodes with 12AX7's or the triode inside the 6BM8? As I understand it the 6BM8is a triode/pentode.

    http://s28.photobucket.com/albums/c2...nt=LWR-MTS.gif

    As a side note, with humbuckers ......... I can get incredibly clear ongoing sustain/overdrive with this amp. I can hit a note and hold it til it feedbacks. My Little Wing Reverb sounds fairly similar to the sound clip of DaGeezer's Little Wing. Although the guy who did that clip is a much better player than I will ever be.

    With respect, Tubenit

  31. #31
    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by Tubenit View Post
    " My main concern is that will the 12AX7s have enough gain to smash the 6BM8 Pentodes"


    Are you going to drive the 6BM8's pentodes with 12AX7's or the triode inside the 6BM8? As I understand it the 6BM8is a triode/pentode.

    http://s28.photobucket.com/albums/c2...nt=LWR-MTS.gif

    As a side note, with humbuckers ......... I can get incredibly clear ongoing sustain/overdrive with this amp. I can hit a note and hold it til it feedbacks. My Little Wing Reverb sounds fairly similar to the sound clip of DaGeezer's Little Wing. Although the guy who did that clip is a much better player than I will ever be.

    With respect, Tubenit
    Yes, the 12aX7 will be the preamp tube.
    The triodes in each 6BM8 will be the triode that drives that tube if a LTP... or if a cathodyne driver then one 6BM8 triode will drive the cathodyne, which will be the other triode of the 6BM8.

    The chassis I have is so small, 5 nine pin sockets is totally out....I don't think I can get even one more 9 pin socket in so reverb is not happening in this one..
    Bruce

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    Here's a cool take on a 6BM8 SE

    Hey Bruce,
    how's you 6BM8 project going? Can you hear any differences between NOS 6BM8 and current production stuff?
    To my old ears they sound very very close.

    To be true to the topic title (6BM8 tubes - what to use them for) - here it goes:
    Myself and another pretty well known Swedish designer - it should be is easy to identify him once you've watched the vids) - have been working on collaborative project involving 6BM8 tube since summer 2007. The result was premiered on May 10-11 at the FUZZ Guitar Show here in Gothenburg.



    It's a hybrid with solid state discrete (no opamps) preamp, goes from NEAT to OTR (On The Rocks), toggle on top adds rocks to the neat whiskey in the jar.

    "Louder" knob does what its name suggests.
    "&" knob operates on edges of the "rocks" smoothing them out or roughing up.

    "More" knob is, if I may say so myself, a real innovation in tube amp circuits.
    You've seen the Triode/Pentode or Triode/UL/Pentode switching arrangements before.
    This does "More". Operating mode of the power tube is continuously variable between triode and pentode with varying degrees of UL mode in between. Besides the obvious reduction of available output power in triode mode it also provides some presence/edge boost as the knob is turned more towards UL/pentode modes.
    Output Power in pentode mode is ca 3W, in triode mode drops to about 1W.

    No decision yet as to when, if at all, this will be released as a product. We did it just for fun.
    The MORE circuit is PAF.

    Vids: LouderAndMore
    Last edited by Alex/Tubewonder; 05-25-2008 at 10:41 AM.
    Aleksander Niemand
    Zagray! amp- PG review Aug 2011
    Without the freedom to criticize, there is no true praise. -Pierre Beaumarchais, playwright (1732-1799)

  33. #33
    Senior Member
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    "these go to eleven..." and a half...

    jamie

  34. #34
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    Eagerly awaiting your final layout Bruce... Been looking for a low-watt ECL82 layout.

    Nate

  35. #35
    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by Natedawg63 View Post
    Eagerly awaiting your final layout Bruce... Been looking for a low-watt ECL82 layout.

    Nate
    I've been working a little bit with this project off line with Jeff... tubenit ... and other then some minor tweaking to fit my chassis, actual working parts values and combine it with a layout I already started, he has a nice layout going so it shouldn't be to long before I can get it in high gear.
    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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