just done this

[Global]

Originally Posted by Paul Barker

but just found out the post office have told him I didn't go to collect it. I don't recall seeing a card for it, but I suppose that's now lost!

Hi Paul

This is a very common ruse used by sellers who simply have not sent out the goods and one I experienced myself a few months ago. Apologies if you know and trust the seller but it could be worth checking!

Mark

[James D]

`Re-reading my first post it sounds quite harsh - that wasn't my intention.

It's an interesting idea and clearly sounds OK as Pete and Doug keep recommending it and people who try it either like it or quite like it. And I applaud Dave for trying it and reporting his findings - he builds a dozen amps to every one I do!!!

But I feel frustrated by the e-linear because it is impossible (for me) to work out exactly what is going on inside the first pentode - the output one you can sort of think through but the first one....

I claimed five feedback loops and a few people have asked me how I get to five - my son included - as that seems a lot so I need to set out my reasoning. Here is how I got to five.

Firstly, the pentode has five discrete inputs and an input signal that affects the output can be generated by any differential signal between any pair of inputs - that gives us 4+3+2=9 ways to input a signal into the pentode. And the feedback loop to each input pair can be either local or over both stages - so 18 generic possibilities in a two stage amp and ignoring amplifier input and output connections in the feedback loop paths. So maybe 5 isn't that many after all… Then there are the possibilities for each loop to be a current derived feedback loop or a voltage derived feedback loop and of course it can either shunt or series derived or applied… Umm lots of possibilities… maybe it is more than five! And of course in the real world it is more than five as the psu and ground points are not clear of signal influence either but for the purposes of this discussion lets stick to just explicit signal paths and see if we can find five terminating on the first valve.

Explicitly we have connected the ultralinear tap on the output transformer back to the top of the load resistor and to the top of the screen grid resistor so we have output signal derived voltage feedback applied to the anode and the screen grid of the pentode. For the anode it’s primary effect is to vary Va (we’ll look at secondary effects later) and as Va is increasing B+ is reducing so this is negative feedback.

For the screen grid the primary effect i.e. Vsg is actually decoupled by the capacitor between the sg and ground so voltage feedback at the screen grid is removed but as B+ is reducing we are still reducing the current following through the screen grid resistor so the current flowing through the cathode resistor is reduced and we end up with secondary feedback applied to the input circuit since Vg-c changes…and again this is negative feedback.

Going back to the secondary effect of modulating B+ with the output signal also modulates the current Ia and therefore the current through the cathode resistor and we have again negative feedback applied to the input grid (Vg-c varying)

So three loops so far all derived from the ultralinear tap on the output transformer.

Local loops are the conventional ones generated by an unbypassed cathode resistor i.e. direct effect of Ia varying by the input signal to the valve and the direct effect of Isg varying by the effect of the input signal.

That makes the five loops explicitly:

Va variation caused by ultralinear modulated B+
Vg-c variation caused by ultralinear modulated B+ modulating Ia
Vg-c variation caused by ultralinear modulated B+ modulating Isg
Vg-c variation caused by Ia modulation of Vg-c via Rc
Vg-c variation caused by Isg modulation of Vg-c via Rc

This ignores the loops through the output stage or the effect of the speakers reflected impedance through the output transformer – both via the ultralinear tap and by direct modulation of the load on the output valve…

Then there are the effects on and loops through the psu both B+ and ground lines…

Now work out what is happening as these all interact dynamically under real audio signal conditions…

One thing is sure – there will be much more intermodulation distortion in this circuit than in the conventional ones.

Hope that explains a bit about why this circuit frustrates me :0

James

[Paul Barker]

James, if you say aso.

Mark, Probably same seller Ian dealt with I don't think it would have been him.

Quite possible the way things work in our house for the card to be retained by wife in handbag until forgoten about. I might never have known. Customers are always saying they have given messages for me I never get. This is not a criticism of my wife just an rational explanation of what may have happened from past experience.

The fact is post office kept parcel having issued warning they couldn't get it through letter box once and then given up on me. So what do they do with it after that?

I got my answer as soon as I'd posted the above "Hi Paul

The post office i guess must have tried to deliver it on 24/1/06 but to no avail. Like I said it arrived back to me a couple of days ago
The box is a little beaten but the contents are fine.I can reship it to you at cost (£4.52)and try again. Please can you forward by paypal the carriage charges and I will be able to post Friday Lunchtime.After that, I am afraid I wont be in the country for two weeks - On honeymoon of all things !

Please answer ASAP so we dont miss the window
thank you in advance Paul
best regards
Jon (Stratos2l) "

[James D]

Hi Paul,

Yeah, I know. If you want to know how it works then build the damn thing and listen to it! Saves all the prating about worry about what it might be doing :-)

Thats where you and Dave put me to shame...

James

[Paul Barker]

I'm more like you not getting anything finished these days. No time for it.

[Ianm2]

hmm I had no probs at all with the seller, only thing is he has no contact tel. no. even on the blurb inside the box, and I wanted to try a couple of his other items, alas, seems like he has supply problems, I reckon they are put together in china

there has been a few occasions where royal mail have left items in my porch, sometimes rather expensive ones, and I have been out, I would be rather peeved if they had got nicked.

[Paul Barker]

Interesting he's going away for a few weeks.

Wonder if he's a foreign student suplementing his studies by frequent visits to Hong Kong to stock up on audio products and smuggle back to blighty?

If I wasn't gainfully employed I might give that a go.