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E55L in triode as driver!

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Hello Tube-DIY-er's,

i wanna drive my 6c33 SE Amp with the famous E55L in triode modus with an interstage.
Like this:
Driver E55L, Output Tube 6c33.
I have got several interstage on stock: pairs LL1660/18mA
Tribute 1:1 20mA
Has anyone experiences with the E55L in triode modus with interstage. U, I?
Would 20mA adequate for the E55L because my interstages can't handle more than 20mA!

Thanks

Barossi
 
Konnichiwa,

barossi said:
Would 20mA adequate for the E55L because my interstages can't handle more than 20mA!

Yes. I find that High Transconductance Valves when driving Output Triodes sound much better at lower current than they do at high current, but of course, "better sound" is personal and subjective.

Sayonara
 
Re: Re: E55L in triode as driver!

Kuei Yang Wang said:
Konnichiwa,



Yes. I find that High Transconductance Valves when driving Output Triodes sound much better at lower current than they do at high current, but of course, "better sound" is personal and subjective.

Sayonara

Hello Thorsten,

i count on you....thanks a lot!
o.k. i will try to fire the E55L with ~20mA, using the tribute interstage 1:1 and connect this to the grid of the 6c33!
How much Plate Voltage is your commendation for the E55L?
So i will connect the G2 to anode, G1 the real grid. But what to do with G3?
What's your opinion about that projekt? (E55L -- Interstage Tribute 1:1 5K, or LL1660/18mA---6C33 SE, 200V, 200mA)
Bias for the 6C33 like:

http://www.users.globalnet.co.uk/~valveamp/images/SE108IT2.GIF


Have a nice day....

Barossi
 
Re: Re: Re: E55L in triode as driver!

Konnichiwa,

barossi said:

o.k. i will try to fire the E55L with ~20mA, using the tribute interstage 1:1 and connect this to the grid of the 6c33!
How much Plate Voltage is your commendation for the E55L?

I like to set the initial operating point for High Transconductance Valves fairly simple.

1) Set the anode dissipation to no more than 1/2 rated.
2) Set the Anode Voltage to about output Valve Bias *2.5
3) Check that your Bias is high enough to allow an input 3db higher than that neede to produce a voltage swing equal to the Bias of the Output Valve.

With your 6S33 Operating Point I get a Bias of 68V from the ANode curves I have. So the E55L Anode Voltage should be around 150V or a little higher at 155V to make using the curves easy. For that the Bias will be around 5V and the Anode dissipation 3W, well on the save side.

So actual +B is 160V plus 20mA * IT DCR, the cathode bias esistor should be 250 Ohm and ideally I'd provide a clean supply and use the "ultrapath" cathode bypass connection with a nice juicey big oil or film cap.

Anode impedance of the E55L looks a little above 1KOhm and gain around 30, so theoretical voltage swing before the bias is exceded is 300V P-P, that is well over 6db input overload margin, excellent.

So, I'd try 250 Ohm Cathode Resistor and 160V on the Anode for starters. Then move a little up and down with the Anode voltage by adjusting the regulator or droppwer resistor for the frontend and listen.

barossi said:

So i will connect the G2 to anode, G1 the real grid. But what to do with G3?

Connect to the Anode of course.

barossi said:

What's your opinion about that projekt? (E55L -- Interstage Tribute 1:1 5K, or LL1660/18mA---6C33 SE, 200V, 200mA)
Bias for the 6C33 like:
http://www.users.globalnet.co.uk/~valveamp/images/SE108IT2.GIF

Sounds fine to me.

Sayonara
 
Re: Re: Re: Re: E55L in triode as driver!

Kuei Yang Wang said:
Konnichiwa,



So actual +B is 160V plus 20mA * IT DCR, the cathode bias esistor should be 250 Ohm and ideally I'd provide a clean supply and use the "ultrapath" cathode bypass connection with a nice juicey big oil or film cap.

Sayonara



Hi,

what do you mean with "ultrapath" cathode bypass connection?
How large should the value be?

I have problems to understand how connect the getters of the E55L: The only think i know so far is G2 to anode! What about G1 and G3.

I will build tomorrow the driver stage using:

E55L in triode connection with ~160V at the anode.
Lundahl LL166o/18mA in connection ALT S with ratio 1:1,125.
Kathode R 250 Ohms, gives ~20mA, bypassed by a Oil-filled C.

Thanks a lot

Barossi
 
Re: Re: Re: Re: Re: E55L in triode as driver!

Konnichiwa,

barossi said:

what do you mean with "ultrapath" cathode bypass connection?
How large should the value be?

Look here:

ultra2.jpg


Pretty much the same circuit, except E55L and 250 Ohm Cathode resistor and 160V +B.

barossi said:

I have problems to understand how connect the getters of the E55L: The only think i know so far is G2 to anode! What about G1 and G3.

G1 remains the control grid. If you wish to triode connect ANY pentode, connect both G2 & G3 to anode, if G3 is freely available.

Sayonara
 
Konnichiwa,

fdegrove said:
Sorry, I don't get this...

Shouldn't g2 be connected to the anode and g3 to the cathode or grounded in case fixed bias is used?

Ever heard of triodes with a screen grid? The screen grid will alter the transfer function. To truely triode a pentode (even an EL34) connect G3 to anode, fixed bias or not.

Sayonara
 
diyAudio Senior Member
Joined 2002
Hi,

Ever heard of triodes with a screen grid? The screen grid will alter the transfer function. To truely triode a pentode (even an EL34) connect G3 to anode, fixed bias or not.

While I do agree with you...

I just wondered why the Philips datasheets state Vg3 at 0V for a triode connected E55L.

As these datasheets don't provide operating curves for your suggested connections, I assume you draw the curves yourself and pick operating point from that?

Cheers, ;)
 
Konnichiwa,

fdegrove said:

I just wondered why the Philips datasheets state Vg3 at 0V for a triode connected E55L.

They cannot seem to be able to make up their minds. I have equally seen datasheets with both extra Grids anoded....

fdegrove said:

As these datasheets don't provide operating curves for your suggested connections, I assume you draw the curves yourself and pick operating point from that?

The term is extrapolating. And G3 does not change the operating point (which is intended as "first cut", to be further optimised by listening) that drastically. The curve shape does though in some areas.

Sayonara
 
Ultrapath

Hi,

what exactly does the Ultrapath capacitor. I have huge Leclance 50uF/500V + 20uF/500V (i think MP's) Cans on stock. I think i will use them.
I have problems with the following:

After switching on the Amp the 6C33 the operating point at 200mA will reach at about 20min. What could i do against this problem? Could i use a mixture between fixed bias and cathode resistor? (I use now a 10 Ohm resistor at the cathode just to measure the voltage drop with adjustable bias between -50V to - 100V)

Greeting + Thanks

Barossi
 
diyAudio Senior Member
Joined 2002
Hi,

They cannot seem to be able to make up their minds.

Yeah...Yet I can understand their reasoning: add a grid to the anode (g2) and another to the cathode (g3) and hope it will balance itself out for most applications.

For all audio purposes I'd tie both grids to the anode, makes more sense to me.

We now have a new valve however and I've no idea if this is going to respond to the laws of physics the way I think it should.

TRIODED PENTODES.

Fascinating how you can make new tubes just by tieing some elements to others...

Frightening for those of us having to work "blind" on this though....

Cheers,;)

P.S. I vaguelly recall a technical article stating that if you wanted true triode operation for a valve such as an EL34 you needed to tie g2 and g3 to the anode....
If only I could recall where I read it....:xeye:
 
diyAudio Senior Member
Joined 2002
Hi,

what exactly does the Ultrapath capacitor.

Very short answer: it keeps DC out of your xformer.

After switching on the Amp the 6C33 the operating point at 200mA will reach at about 20min.

That's normal for a 6C33C.

What could i do against this problem? Could i use a mixture between fixed bias and cathode resistor? (I use now a 10 Ohm resistor at the cathode just to measure the voltage drop with adjustable bias between -50V to - 100V)

You can but that's not going to solve that particular problem...
The 6C33C has huge cathodes, so they need time to reach cruising speed.

Just don't play music full blast before they're properly warmed up, you'll hear the distortion right away and they may pop a fuse or cathode resistor if you do.

Cheers,;)
 
diyAudio Senior Member
Joined 2002
Hi,

Thank you for the reply.

From experience - yes, with E810F, E180F, C3m, EL34 and EL84.

While I do absolutely believe you on this, it's a pity no hard facts seem to be publicised regarding this.

If there are I'd like to be directed to some more precise info even if my instincts and common sense tell me Thorsten is absolutely right here...

Ta,;)
 
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