Single tube SE with EML-20B

[tinitus]

Hey, you probably think now I must be completely daft to even try

I hope you can help me to at least get a bit better understanding of how it works

I have never done anything like this before, at all

EML-20B is a driver tube, and a power tube, if Im correct
This means that it can work on its own, without driver tube

Well, I found a 300B schematic, and changed a bit here and there
Maybe not the best start really
Some details havent been changed yet
and some changes I have made may be wrong
something I just did in a hurry, without having much clew about it

Im not expecting anything
and I know I should better let it go
but it tickles my curiosity

[tinitus]

a bit more work on schematic, bias curcuit

[tinitus]

more schematic work
still in doubt how it works

[kevinkr]

I previously replied, but deleted my post as a result of doing a little research on this tube..

I see the EML-30B has a mu of 20, rp 3.3K, recommended Ip of 60mA and a pd of 25W. This means that an SE output transformer with a primary > 10K is required - this is actually not a trivial endeavor, and a suitable quality OPT will be very expensive.

The current proposal requires the use of both an input transformer and an auto-transformer which will severely compromise both the LF performance and the HF performance. A single transformer with a ratio of 1:10 would provide sufficient gain, but also a rather low input impedance for good performance - the impedance transformation ratio would be 100:1 implying a 60K secondary with a 600 ohm input Z, possible, but is it wise if any significant current ever needs to be delivered to the grid? (And it will result in problems with the high frequency response due to interaction with the miller capacitance of the 20B)

Seems like a low mu triode like a 6J5 would do a much better job driving the tube, providing a low driving impedance to the grid of the 20B and a high input impedance and sufficient voltage gain to assure it works with real sources.

I'd go with fixed bias in the output stage were it me, this would allow easy tuning of the operating point if desired and eliminate a fairly lousy capacitor in the output stage cathode circuit.

The killer IMHO is the output transformer requirements, at these impedances I would definitely suggest a c-core as the most viable choice if you want decent HF performance. Maybe AE, Bartolucci or Lundahl have something suitable?

[tinitus]

yeah, you are pointing at exact some of the worries I have had
and explaining why, thanks

please note that grid choke is a Lundahl, supposed to give a 1:2 gain, configured like this

I also thought using input trafo for gain, maybe takes care of DC, thus no cap needed, but I dont know

And I have considered a need for use of tube preamp, maybe

[Jaime]

Gordon Rankin do it:
Mercury Series, Single Stage, Single Tube Amplifiers
Wavelength Audio Single Ended Mercury Series
I believe AVVT 20SL (VAIC) >>> EML-20B (Emisión Labs)

The Mercury skema is not published but Gordon post this in other forum
MagneQuest/Peerless Forum: Simple 84 by Gordon Rankin

[tinitus]

hey, that single tube EL84 SE schematic might be useful
great

regarding AVVT vs EML
yes, same people
but I think designs have improved
Jac(Germany) is now the owner
seems to be in safe hands
ofcourse, using such a tube always presents certain risks
how long will they be around etc

btw, I also chose 20B because its relatively affordable
and I found it interesting
but hey, this is so far just a learning exercise
and sorry to say, it probably stays that
in the end I will probably choose a design I know works
but I learn a bit here and there, small stuff

hey, I made my first schematic, stealing bits and pieces
does it work ?
I have no idea, but I somehow doubt it

Im open to all suggestions

[nicoch58]

Bob's EML 20B One Tube Single Ended Amp

[tinitus]

Hey, I know Min´s site, its very nice
Bob´s amp ?
Wonder who designed the schematic
I could try and ask Min
its great, thanks

[tinitus]

Originally Posted by Jaime

Gordon Rankin do it:

The Mercury skema is not published but Gordon post this in other forum
MagneQuest/Peerless Forum: Simple 84 by Gordon Rankin

grid choke with gain, at least I got that part right, well almost

the one with plate choke, I have no idea
it looks kind of more real to me, dont know why
connecting B+ power directly to OPT always puzzled me, thou I know its the usual way it works

hey, I know where grid and plate is now, thats worth something