Oops, Dyslexia on ebay causes man to buy a sleeve of 6MB8's

[chopstuck]

OK. figured it out after buying and after item shipped. Wanted 6BM8's

Now, what can I do with this pentode/triode affair ? I looked it up and found a few hi-fi uses but I was hoping for maybe a reverb drive pentode and recovery in one tube. Looks like a High-Mu Triode - Sharp-Cutoff Pentode.

Specs here- http://www.nj7p.org/Tube4.php?tube=6MB8

Found this too http://imageshack.us/f/225/ideay.jpg/

With 2 watt dissipation on the pentode maybe it can drive a reverb pan ...

Otherwise will I just have to chalk it up to late nite blurry vision and take a loss.

[Leviman]

It's okay, I bought a box of unkown tubes for $20 once. Turned out I didn't recognize any of them and can't find a use haha. But someday I will gain the skills to design a circuit from a datasheet and build crap out of all of em!

[tubeswell]

There's heaps you can do with 6BM8s.

The triode is a 5751 equivalent. The pentode is not unlike a low-powered EL84 - 7W max dissipation if plate voltage <250 (or 5W above 250) into a 5-6k load resistance, bias of about -24V, screen 200V, plate 300V

[10thTx]

EDIT: I did not read the original post carefully enough. Sorry. At any rate, perhaps you could look at these editable schematics for ideas to consider.


Some of these are editable ExpressSCH schematics and layouts.

There is a 56T 6BM8 reverb amp schematic and layout here:

http://www.el34world.com/Forum/index.php?topic=6176.0

There is a "Little Wing" mini-bassman with 6BM8 tubes here:

http://www.el34world.com/Forum/index.php?topic=562.0

There is a 6BM8 one tube reverb schematic here:

http://www.el34world.com/Forum/index.php?topic=7957.0

With respect, 10thtx

[da Geezer]

If I'm understanding correctly...........

He WANTED/INTENDED to get some 6BM8's, but instead bought 6MB8's by mistake
& now wants to know what he can build with them.

G

[chopstuck]

Geezer, I built several of your low power designs and like them a lot. That's what those tubes were for. I used your 6BM8 power section for a champ preamp that absolutely kills. It's driven pretty hard so I'm not sure if the switchable NFB does anything. Everyone who has heard it, likes it.

BTW, it makes me feel better that two people have already made the same mistake that I have !


6BM8 vs 6MB8

[tubeswell]

If I'm understanding correctly...........

He WANTED/INTENDED to get some 6BM8's, but instead bought 6MB8's by mistake
& now wants to know what he can build with them.

G

Bugger it! I've got the same dyslexia!

[renshen1957]

OK. figured it out after buying and after item shipped. Wanted 6BM8's

Now, what can I do with this pentode/triode affair ? I looked it up and found a few hi-fi uses but I was hoping for maybe a reverb drive pentode and recovery in one tube. Looks like a High-Mu Triode - Sharp-Cutoff Pentode.

Specs here- http://www.nj7p.org/Tube4.php?tube=6MB8

Found this too http://imageshack.us/f/225/ideay.jpg/

With 2 watt dissipation on the pentode maybe it can drive a reverb pan ...

Otherwise will I just have to chalk it up to late nite blurry vision and take a loss.

Hi,

Check out

http://www.ampbooks.com/home/amp-techno ... -power-amp

Good place to start.

Best Regards,

Steve

[Phil_S]

This is lemonade, not lemons. Look at the data sheet. There's nothing way out about the tube specs, so I think you should give it a try.

As long as you are trolling eBait, look for a cheap 25.6V filament PT that has plenty of current capability (1A is actually more than enough; you only really need about 250-300mA rating). See if you are lucky enough to get one that is both 25.6V and 6.3V. (I have such a thing.) For a two tube amp, you'll need 0.8A on the 6.3V filament supply plus a little something for a pilot light, so make it 0.9A.

Run it through a 2x doubler (I mean 4x total) and you'll get about 140VDC at the first B+ node. This should be perfect for a pair of pentodes. Use the triodes for the preamp - 3 gain stages into a concertina, or 2 gain stages into a LTP. Treat the triodes like a 12AT7 (which is why I am thinking about the concertina).

Or, make a single ended amp with only one tube. It's your choice to drive the triode with the pentode or the more conventional triode driven pentode.

For not too much money, you might get something fun and a little off the beaten path.

[10thTx]

Deleted schematic after learning 6MB8 is probably not a good guitar tube amp power tube.


With respect, 10thtx

[chopstuck]

Thanks Phil, I will keep the tubes and maybe, I will have a little extra winter project.

[chopstuck]

Hol-ley COW ! 10thTX,

Did you just draw that up ???

THat's a bit similar to the 56T 6BM8 I'm working on now. I mean right now.

In fact, it answered my question about what the switch does that disconnects the bass and mid control - must be PAB.

I built mine as drawn minus the tube recto for now.

THe amp sounds good, really good.

This is the busiest amp I've built to date. Mod switches and reverb.
I believe it sounds better than the Little Wing and I liked that amp really well.

[10thTx]

Deleted schematic after learning more about 6MB8.

10thtx

[chopstuck]

Interesting TOS.

What kind of OT impedance would you need ?

I have a box of old OTs. I have a small push-pull 12BH7 Hammond organ reverb transformer that's the size of an AO-35 OT. I will have to measure the turns ratio but sometimes close enough is fine.
What kind of wattage do you think ? Do you think a reverb power tranny would work 100ma and a 6.3v heaters x 3a

[Phil_S]

Thanks Phil, I will keep the tubes and maybe, I will have a little extra winter project.

While we're at it, I've got some 6AC7's I'll sell ya! Got 'em cheap. I wonder why?