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

[Bruce / Mission Amps]

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.

[Chuck_Farlee]

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

[Albert Kreuzer]

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

[Bruce / Mission Amps]

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.

[JoeM]

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

[Ben N]

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?

[echuta13]

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.

[Bruce / Mission Amps]

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 / Mission Amps]

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 / Mission Amps]

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

[imaradiostar]

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

[sportster4eva]

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?

[tubeswell]

Found a circuit for ECL86 (not ECL82)

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

Don't know it its much help

[Bruce / Mission Amps]

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.

[Bruce / Mission Amps]

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.