Single Ended EL34 amp

[The Shadow]

Well "Rocky the rebel kid brother of old Loftus White is now under construction.
Check out the story so far here http://web.mac.com/scress1958/iWeb.

Steve

[david counter]

very nice Steve,
btw.what did you use for the bus bar?

[The Shadow]

Hi David

The bus bar branches were made out of the centre conductor from some ordinary twin and earth mains cable. This is 1.6mm dia.
The main bus bar running from ground terminal at the mains inlet then along the centre of the chassis was made from one of the insulated conductors with the insulation stripped at 2.5mm in diameter.

Steve

[The Shadow]

Well Rocky is finished

It's in the system and running in. Initial impressions are good. It's fast, clean and neutral without a hint of harshness or nastiness. Hopefully it'll get even better over the next few days.

Th final design was built around a single NOS RCA 6SL7 dual triode. Each half driving a Svetlana EL34 in triode mode... Nice...so far. We'll see how it pans out.

Steve

[The Shadow]

Edit: The pics of the whole build are up now. http://web.mac.com/scress1958/iWeb/

I've built a new website dedicated to the people on this BB who freely give their time and advice to help folks like me. If anyone wants to put up pics and stories about their own builds and experiences I can host them for nowt. We could develop this into a nice resource if the willingness is there. It's about time we had a showcase for our best projects/system pictures etc. The Eggfest 1 and 2 pics are going to be brought over in the near future pictures intact but with a bit of a commentary in newsletter format

PM me with any stuff you want putting up
Steve

[Greg.]

Hi Steve,

Well done mate, both on the amp and the website.

I wonder, if you are willing to develop and manage this site featuring stuff from this forum, it's members, their collective activities and of course WD if it could be given a 'sticky' with it's own place on the index for ready access to all. It could also be a useful asset to WD in support of the company. Maybe you might like to talk to Peter about this.

Anyway, I like the build on your amp. If those 4K7 10W coffins generate alot of heat, they'll be cooking stacked like that, but I'm sure you've thought that through Lovely job of a scratch build and a fine example to others of what can be done after just a few months playing and learning in this hobby.

Best wishes,

Greg

[The Shadow]

Hi Greg

Thanks for the positive comments.

Those big cathode resistors are a bit of overkill on my part. There was only supposed to be 1 resistor there. My calcs on the back of a post-it had come out at around 900R for the bias I needed. I could have therefore used an 880R 25W wirewound but too late in the day I found that I only had one to hand. I did have a dozen 4k7s knocking about so putting 5 in parallel on each side gave 940R which was as near as made no odds. They only get slightly warm so stacking them was not a problem, unlike the Loftin-White where they had to have their own venting arrangements they got that hot.

The most important thing I've learned over the past six months reading these forums it's that when working with valves there are an awful lot of variables to contend with and it seems to be a matter of juggling them around until you get the best compromise.

The website as you say Greg could do with a separate thread I'll see what can be done about this.

Steve.

[simon2a3]

Well done Steve, I look forward to having a listen sometime.

You went with a triode driver rather than pentode after all?

Simon.

[The Shadow]

Originally Posted by simon2a3

You went with a triode driver rather than pentode after all?

Simon.

Hi Simon

Truth is I'd bogged myself down with loadlines etc and simply couldn't think what pentode to use. Too many alternatives. I very quickly discovered that I'm not sufficiently experienced at present to make those sorts of decisions having only been at the valve game for 6 months.
I decided to stick with the simple and familiar and to return to Paul's initial advice about not parallelling both sides of a double triode due to Miller capacitance.
I figured that I could reduce this effect by using just a single 6SL7 and using each half as a separate triode going to left and right EL34s respectively. Less plate area in the driver, less capacitance, and a simpler valve arrangement.
I could cope with this and the maths involved by studying Morgan Jones, perusing published circuits and taking it steady; not trying to do too much too soon.

The results have been very encouraging. The amp sounds very nice indeed and I've learned a great deal on the way.

Steve

[The Shadow]

Right!

I've been listening to the amp for the past week and it has settled down nicely. Initial impressions of a fast, clean, tuneful and neutral sound have not diminished. It has a lovely liquid smoothness to it which is delightful to hear.
There is no hint of any nastiness anywhere in its range. It has that wonderful all-day listenability that valve amps are supposed to possess.

The original design requirements that it be a sort of retro fifties/sixties rock and roll amp have definitely been fulfilled. It sounds great with Elvis, Beatles etc and gives a real sense of performance with all kinds of stuff from jazz to blues and soul. I like it (but then I would wouldn't I).



If anyone wants a look at the circuit, I've put it up for download at the website. Just follow the "Download Links" when you get there.
http://web.mac.com/scress1958/iWeb

Cheers
Steve