ECL82 Question

[Neil Purling]

Do the triode & pentode sections have characteristics of gain matched by separate triodes & pentodes?
In the same way as the ECL86 is half an ECC83 and a EL84 in the same envelope.

[bikerhifinut]

Not quite as far as I can ascertain from my mullard Valve data book.
The triode section has similar limiting characteristics as an ECC83 in terms of max Pa and Va etc, but the gain is a lot lower with a mu of 70 as opposed to 100 for the ECC83. Thats slightly better than an ECC81, its characteristics look similar to the ECC81 in some respects. So I'd hazard a guess and say if you ran it like an ECC81 then it'd get a result.
By the way The ECL86 may well have had an EC83 (one triode) in the envelope but the pentode wasnt an EL84, more like an EL81 I'd say, as is the ECL82 with a max pA of 7W. Against pA of 8W for the EL81. EL84 max Pa is 12W, from Mullards own data.
I havent got the figures for the ECL86 in my book.

Hope that helps.

A.

[Neil Purling]

Sounds like more than enough for my needs.

[DangerMan]

For ECL86 Pa max is 9W and gm is 10mA/V... both figures identical to EL41 rather than EL84.

For ECL82, gm is much lower than this at 6.4 mA/V with 200V Va and Vg2, and I don't think there is a "near equivalent" pentode.

Pete

[Neil Purling]

Are there any known stability issues to be aware of when laying out the components under the chassis?
I just didn't want to get into something that was twitchy, like an ECL80 is.

[Sideband]

The ECL82 is quite a good valve and as long as your layout is neat, there should be no problems. The main difficulty with the ECL80 is it's common cathode and unless you take great care with the layout and design, it has a tendency to act like a cathode coupled oscillator! Most designs using the ECL80 had neutralising capacitors between anode and grid. You shouldn't have those problems with the ECL82.

I actually liked the little ECL80 and had great fun with them in the early days.

[Neil Purling]

I have seen a circuit, but the volume control has not got a value. As it's track is also the grid resistor I am wondering what sort of component value is called for? I am guessing at a value between 470K and 1M.

[kalee20]

The ECL86 is actually a beam tetrode, not a pentode, if you look closely at one (don't believe the data sheet!)

The ECL82 triode is similar to half a 6SL7... But only similar, not identical. Dimensions are different, so it wouldn't be the same! The pair are designed to be compatible as a driver/output combo, and they succeed pretty well. Cramming them both in the same envelope, too much gm in the pentode would have made the thing too prone to parasitic oscillations.

[dominicbeesley]

Here's my first ECL82 amp - while I was still near the left on the Dunning-Kruger graph, not that I've moved much.

ECL82's - they're cheap and plentiful. I never did get round to fitting the feedback network but it sounds fine until it's over-driven. I didn't have any trouble with HF oscillation but a few issues with hum pickup and microphony on the PCL82s

If I were to do it again I suspect I'd go with ECL86's, I just started with PCL82's as I was skint at the time and happened to have a pile of them to play with.

If you're feeding the input from something with a low impedance output (solid state pre-amp or direct from a CD player or computer), a lower resistance pot can help reduce pick up.

D

[Herald1360]

Originally Posted by dominicbeesley

Here's my first ECL82 amp - while I was still near the left on the Dunning-Kruger graph, not that I've moved much.

Errr where is it?

[dominicbeesley]

Oops, sorry, http://www.brahms.demon.co.uk/softwa...2_1/index.html

[G4XWDJim]

In your link the point is made about 'star' earthing but it's not an easy thing to do when you consider that the bodies of pots and large electrolytics are invariably bolted down to deck.

I've never found an easy way around that issue.

Jim

[Herald1360]

The body of a pot can be decked without affecting the track connections which can relate to the star point. Elkos can be sleeved quite easily. If necessary a bit of tinned copper or even steel shim can be clamped in the mix to get the negative connection out if there isn't a specific tag.

[dominicbeesley]

As Herald said there are ways around the chassis mount problems. I used plastic bodied pots (because that's what I had). Most pots have the track isolated from the shield just don't earth the track to chassis but to the star point.

The PSU is in a separate chassis altogether on that amp so not such a problem about electrolytics. However, on another OTL headphone amp I did I made some simple gaskets out of plastic to isolate the smoother from the chassis. On other things I've made I put the star point at the smoothing caps. There are other ways your grounds can be done, I've found star grounding to be reasonably foolproof.

D

[julie_m]

The star topology ensures that no earth connection is in series with any other. This is not always necessarily as easily done as said, but what is most important is not to have high-current paths effectively in series with small signals; current through a resistance develops a voltage across it, proportional to the resistance; and if this resistance is in series with a signal, it will interfere with it.

Redrawing the wiring diagram will help you spot where the heaviest earth currents are going to be flowing.