would this work? SE EL84 circuit

[bikerhifinut]

Ok gents,
An enforced spell indoors with a very nasty lung infection has left me with little else to do but research circuits.
I was looking at this circuit on Danbury Transformers site and it appealed to me as a possible alternative to the 3-3 circuit.
However I'm not entirely sure how much current the EL84 will draw nor do I really know how to work out the feedback resistor value. The circuit looks a bit incomplete. I thought it would be a good use of a spare 6CG7 valve as part of a stereo amp and save on a valve socket too. (limited space on the chassis). The circuit looks a bit too simple to have any pretensions to quality.
Andy.

[pre65]

Originally Posted by bikerhifinut

Ok gents,
An enforced spell indoors with a very nasty lung infection has left me with little else to do but research circuits.
I was looking at this circuit on Danbury Transformers site and it appealed to me as a possible alternative to the 3-3 circuit.
However I'm not entirely sure how much current the EL84 will draw nor do I really know how to work out the feedback resistor value. The circuit looks a bit incomplete. I thought it would be a good use of a spare 6CG7 valve as part of a stereo amp and save on a valve socket too. (limited space on the chassis). The circuit looks a bit too simple to have any pretensions to quality.
Andy.

Give us a link to the circuit so we can comment.

Do you mean Danbury transformers web site or Mike Holmes (living in the past) web site ?

Is this the one ?

http://livinginthepast-audioweb.co.u...p?p=samp-se-84


*

[bikerhifinut]

That's the very one, i forgot to paste the image in

I told you I was ill.................. hang on isn't that what Spike Milligan has as an epitaph, I ain't that far gone yet lol.SE EL84 amp.gif

[pre65]

Well, I doubt that Mike would post details of a circuit than did not work.

I gave some details of EL84 working in SE mode in your other thread, and the current through the 4K7 resistor would add another 10.6ma (ohms law).

If in doubt, give it a go, and don't worry about the feedback values, just leave it out, it will probably sound better.

Can you resist the temptation to contact Mike Holmes directly as his mum is seriously ill at the moment.

[bikerhifinut]

Originally Posted by pre65

Well, I doubt that Mike would post details of a circuit than did not work.

I gave some details of EL84 working in SE mode in your other thread, and the current through the 4K7 resistor would add another 10.6ma (ohms law).

If in doubt, give it a go, and don't worry about the feedback values, just leave it out, it will probably sound better.

Can you resist the temptation to contact Mike Holmes directly as his mum is seriously ill at the moment.

I wasn't going to contact Mr Holmes but thanks for the information.

I'm just working through the circuit, the values don't match the current on V1 I think. But I need to get a new envelope out to scribble on the back of.......................................

[bikerhifinut]

I think the anode resistor on the ECC82 should be 10K that way passing 10mA it would show about 150V on the anode but if its passing 10mA then thats 47V on the cathode which seems a bit high. I would have to get the curves for the ECC82 and check the operating conditions. Ah well time to attack it tomorrow seeing as I'm banned from going outside and tinkering in the garage.
Thanks so far, looks like the good old 3-3 circuit may still be the best compromise overall.

Andy.

[Richard]

Yes something's amiss in the values, or voltages of the supply, of the first stage.
From the data sheet, with 250V supply, 100K Ra and 2K2 Rk, it would only pass 1.63mA so with 4K7 at Rk it won't pass the 10mA suggested on the HT line.

[pre65]

But, that also includes the EL84 G2 current.

[Richard]

Originally Posted by pre65

But, that also includes the EL84 G2 current.

Ah well spotted Philip, yes, data sheet for EL84 suggests between 5 and 10mA there good job you're keeping an eye on the job

[Richard]

Get well soon Andy by the way, sorry, forgot to say that, got so carried away with data sheets etc still you're not missing much it's cold and foggy down here, roll on Spring