Rca 6md8

[Mosquito]

Hi, I've got a couple of pairs of these tubes
http://www.pmillett.com/tubedata/HB-3/Receiving_Tubes_Part_2/6MD8.PDF
I'm wondering if could be some smart way to use it,
like the input stage of a minimalistic two tube
amplifier, for example. Any suggestions?
Cheers!
JJT

 

[Arnulf]

Any element that is capable of amplification can be turned into an amplifier, but man, is this one oddball choice for audio or what 😀 Common cathode for all three sections, rather low mu, modest current capability per anode, not very linear 🙁

Can you be more specific regarding your idea, namely what kind of input (voltage swing) and what kind of output (load) were you planning to use with it ?

 

[Mosquito]

🙂 Nothing special, think in a "Gilligan Island" situation, you got these, and you want to use in some way. The girls (Ginger and Mary Ann) are asking to hear some music. Something half good will be enough...

 

[TheGimp]

First guess would be to use a grounded cathode and negative bias on the three grids so you could minimize coupling between sections.

1 stage for voltage gain, two stages in parallel for power gain?

 

[Mosquito]

Oh!, I was thinking in 300V, 6K8 at the K, and some suitable R at plates, a grounded K followed by a long tail. But maybe yours is better...
It will never be perfect, need just to more or less work...

 

[Palustris]

You could use it as a three channel mixer; tie the plates together. Tie the plates together and use it as a cathode follower.

 

[Mosquito]

Mmm, cathode follower... with 300V and Rk 10k it can swing better than +/ - 100V, and 100ohm Zout (I'll check, I'm not completely sure of my math..)

 

[cogsncogs]

It's basically 3 6GU7's (similar to a 12BH7) sharing a common cathode. Used primarily as a color matrix amp "color driver" for color picture tubes, so it's fairly linear. Take a look at the curves for a 6GU7. Except for the shared cathode it would make fine all in one input tube for P-P amp. Too bad as I have quite a few of them!

Wayne

 

[Mosquito]

Hi, you mean that the idea of a grounded K followed by a long tail is feasible? (whith the limits and compromises imposed by the lone shared cathode)

 

[Mosquito]

The thing is considerably bigger than a normal 9pin signal tube. And needs a special 9 pin NOVAR socket.
(y tiene el chupete en la parte de abajo)