EL84 as both driver and output stage.

[pwan]

Hello

I have tons of EL84/6BQ5/6P14P around.

I wonder if any one here come across a SE schematic that use EL84 on both driver and output stage ?

Thanks !

 

[SY]

The EL84 is sooooo easy to drive that I can only ask, "Why?" Use the second one in parallel for double the power, then drive 'em with something more appropriate (i.e., less power delivery, which is useless, but better linearity, which is useful).

 

[pwan]

The EL84 is sooooo easy to drive that I can only ask, "Why?"

Simply because I have too many (100s) of EL84 and want to utilize them as much as I can

Any further guidance please? Thanks!

 

[SY]

50 in parallel per channel. Or just use two and send me the rest.

 

[Miniwatt]

 

[pwan]

50 in parallel per channel. Or just use two and send me the rest.

I am serious !!

 

[Yvesm]

A quick check with Tube CAD.

Triode connected, 250V B+, 10K anode load resistor and bypassed 600 ohms in the cathode should produce near 23dB gain.
Just enough to drive another one.
Not so hi anode current (10mA) but still 4,5W absorbed by the heater.

Yves.

 

[KaDe]

EL84 line driver

Hello
The EL84 can work as line driver also.
I have attached a Vollmer pre-amp circuit with EL84 transformer output for you.

 

[Miniwatt]

I am serious !!

Yeah, I know, I was laughing because of SY's reply "50 in parallel per channel. Or just use two and send me the rest."

BTW interesting question

 

[pwan]

A quick check with Tube CAD.

Triode connected, 250V B+, 10K anode load resistor and bypassed 600 ohms in the cathode should produce near 23dB gain.
Just enough to drive another one.
Not so hi anode current (10mA) but still 4,5W absorbed by the heater.

Yves.

Do you mean this?

 

[sorenj07]

30 or so per channel, trioded, in a Circlotron/Futterman or other type of OTL would give you some decent power. Now, the question is, where do you find a 6.3V 30A transformer per channel.

 

[Colt45]

Do you use sledge hammer to install small nails?

 

[Yvesm]

Do you mean this?

Yes, kinda Zen !

With or without cathode bypass on first stage.

Don't expect more than 2Watts output.

Yves.

 

[pwan]

Yes, kinda Zen !

With or without cathode bypass on first stage.

Don't expect more than 2Watts output.

Yves.

I use Foxtext 166e (94bB) so 1.8W triode is plenty enough.

So, will the circuit I attach earlier work?
( sorry, I relatively new to tube design & high volatge, so just wanna be sure first). Thanks

 

[Bas Horneman]

So, will the circuit I attach earlier work?

Yes. I would however insert a 47k or so resistor from grid to earth before the first EL84.

 

[Yvesm]

Yes. I would however insert a 47k or so resistor from grid to earth before the first EL84.

Agreed, or use a potentiometer, same value !

Yves.

 

[SY]

Note that at these operating conditions, the linearity will be mediocre at best. The rp will be something like 6k, which means that with a 10k load, you can expect a few percent THD (dominated by second). Now, you may like the sound of a lot of added second harmonic (it fattens and sweetens the sound), but it is not in any sense accurate.

By comparison, the distortion of a more suitable driver tube will be well under 0.05%, leaving your output stage as the primary distortion contributor.

 

[Bas Horneman]

O yes, you could also bypass the 600Rresistor of the driver tube.

 

[pwan]

Thanks for all your comment. Due to my little knoweldge, not sure if I can grasp them all.

Is my understanding (in the photo) correct?



Also, more questions popped up now:

1) As SY said, should the Rp (in green) be 6K Ohm or 10K Ohm ?

2) To make the voltage at first stage (less ripple) and output stage (more ripple can be) make easier in practice, can I use the B1+ as ~ 315 Volt?

 

[jane]

Rp is the internal resistance of the tube. Rp depends on the anode current, 6k sounds quite high for EL84 in triode mode which means that the current has to be low. In normal operation rp should be more like 2-3k.

Jan E Veiset