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

[tubeswell]

any chance you'd consider parting with a pair?

FWIW Svetlana and EH are making new production ones

[Alex/Tubewonder]

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.

[J Martin]

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.

[imaradiostar]

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

[Bruce / Mission Amps]

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.

[Bruce / Mission Amps]

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.

[Le Basseur]

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,

[Bruce / Mission Amps]

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.

[Alex/Tubewonder]

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.

[Tubenit]

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

[Bruce / Mission Amps]

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 / Mission Amps]

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.

[Alex/Tubewonder]

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.

[Bruce / Mission Amps]

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

[Tubenit]

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