ECL82 PP "reference" amp

[Tyimo]

Hi!

I would like to buid a simple and good PP amp for reference and to listen and demonstrate the sound of the PP tube amps.

I found a couple (or 3-4-5 😀 ) of interesting circuits, but I don't know which one is the best....

Here are the competitors:

- Mullard 7W classic amp
- Audio Innovation 300 Mk2
- Svetlana 6BM8 (from Sansui)
- No name (suggested by Sjef)
- Rainer zur Linde amp

Has somebody experiences with these amps?
Which one can operated in Ultra Linear mode and is it worth it?
For the output transformator I thought on the Hammond 1620.

Greets:

Tyimo

Here is the Mullard:

 

[Tyimo]

Here is the Audio Innovation300Mk2:

 

[Tyimo]

Here is the Svetlana 6BM8-("Sansui"):

 

[Tyimo]

Here is the No name (by Sjef):

 

[Tyimo]

Here is the Rainer zur Linde amp:

 

[planet10]

None of the above (really onlt variations on 2 topologies).

Yves & Gingertube worked out an ECL86 PP with a Long Tail Pair loaded by a CCS and RH style (plate-to-plate) feedback.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=53969

dave

 

[Shoog]

I'm having really good result with the attached schematic of my own design. I'm using it as a headphone amp, but by choosing the correct output transformer you should hget good performance with speakers.
Fully differential from input to output. No cathode bypass on the input LTP. Differential output stage with self balancing bias circuit.

Based on Gary Pimms Tabor circuit. I love listening to it.

PS. R11 should be 800R.

Shoog

 

[Tubes4e4]

Hi Tyimo,

I would suggest to add the German Klein+Hummel Telewatt VS55 circuit to your list. Klein+Hummel (still) is a producer of broadcasting & studio gear and back in the old times also had a line of amps for demanding private customers.

I once had such a VS55 on my bench for restauration, which thaugth me a *lot* on professional circuit design; it has some very interesting aspects almost nobody cares about nowadays for some unknown reasons.

But you can find pictures, description and schematic here at this link.

Sound is outstanding for an amp using "sh*tty TV tubes" like ECL82/6BM8, I can asure you.

A problem for your project will be that the Hammond OPTs you have in mind quite likely don´t come anywhere close to the quality of the OPTs like being used in a K+H VS55 amp or comparable gear. In this regard, you should use really good OPTs in the first place when heading for a "reference" class project 😉

Regards,

Tom

 

[Tyimo]

Thanks Dave and Soog!

None of the above (really onlt variations on 2 topologies).

Dave, sorry, but what do you mean?? Did you answer for this question: "Has somebody experiences with these amps?" or for this: "Which one can operated in Ultra Linear mode and is it worth it?"

Do you suggest this:

Greets:

Tyimo

 

[planet10]

Do you suggest this:

yes.

I have a donor downstairs & that is what i'm going to build. (but in pentode mode -- i don't have UL OPTs

dave

 

[Shoog]

All my previous experience with the ECL82 produced a harsh quality which suggested oscillation or overload. This is a difficult tube to get to sound nice, and I have read variously of people having to try many different configurations before they got something they could live with.
I think one secret is to drive the triode well within its comfort zone, rather than trying to kill gain by application of feedback later on. This always runs something of a risk of swamping the anode current with feedback current such that the quality of the triode becomes lost. This is why I came up with the idea of a step down input transformer. Seems to work very well.

i almost gave up on this valve before i came up with my current circuit. Also I found that Russian made valves sounded a lot smoother than the NOS Mullards which I tried.

Shoog

 

[Tyimo]

Thanks Tom for the infos and the link!

A problem for your project will be that the Hammond OPTs you have in mind quite likely don´t come anywhere close to the quality of the OPTs like being used in a K+H VS55 amp or comparable gear. In this regard, you should use really good OPTs in the first place when heading for a "reference" class project

Yes. I did a little search about the Hammond and I got very disappointed infos. Now I have to find a better output transformer.....

Greets:

Tyimo

 

[Tyimo]

O.K.
I decided to try the classic design suggested by Sjef and the Gingertube variant suggested by Dave.
Now I would like to ask: What would be the best for the OPT??
I know it is the key element and also the weakest point in the designs.

Greets:

Tyimo

 

[planet10]

the Gingertube variant suggested by Dave.

One thing i have to mention now that i've noticed the title is ECL82 not ECL86, is that with the ECL86 you need a bit more gain off the LTP than the triode section of the ECL82 can give.

With ECL82 you'd need to change the feedback (easiest is to just eliminate it and triode the output stage, but you are now down to 3-5W (probably glorious thou) or as suggested by gingertube in a thread on using the RH topology on a SE RHECL82, you cascode the front end either withanother tube or FETs. The cascode does give huge gain, and high output impedance, which gives lots of flexibility for the RH-style feedback scheme.

dave

 

[Shoog]

One thing i have to mention now that i've noticed the title is ECL82 not ECL86, is that with the ECL86 you need a bit more gain off the LTP than the triode section of the ECL82 can give.

One way to make up the gain is to put a input transformer up front. This doubles the effective gain of the LTP, and probably performs better to boot.

Shoog

 

[planet10]

One way to make up the gain is to put a input transformer up front. This doubles the effective gain of the LTP, and probably performs better to boot.

Very good idea... what kind of ratio do you think? It would also reduce (or eliminate the need for the CCS in the LTP tail.

Do you think any of the trafos here could be pressed into service?

http://www.edcorusa.com/products/transformers/wsm/index.html
http://www.edcorusa.com/products/transformers/xs/xs1100.html

dave

 

[Shoog]

Its an extremely undemanding job for a transformer so the range is probably quite wide. I used a microphone transformer with a step down of 9:1. This works very well, and helps to keep the triode from any chance of overloading. Anything greater than 4:1 would be ideal.


None of the first linked transformers seem ideal, but I would say that the second one would definately make a good candidate.
Haven't you got any suitable microphone input transformers from pulled amps. These are extremely good quality and if their like the ones I have, they come in round cans which mount well on the case.

It would also reduce (or eliminate the need for the CCS in the LTP tail

I have used grid leak bias with a single 10Meg resistor on the centre tap. I only have a relatively small resistor below that to finish off the tail as their are no cathode resistors.

Shoog

 

[planet10]

Haven't you got any suitable microphone input transformers from pulled amps. These are extremely good quality and if their like the ones I have, they come in round cans which mount well on the case.

A pair of lovely looking naked Philips ones... i haven't measured them but had in mind MC step-ups. I do have some phase split transformers from early SS gear that i thot might work too. Just always looking for an excuse to try out those Edcors.

dave

 

[planet10]

I don't believe anything, but I have many suspicions.

Robert Anton Wilson

I've had the opportunity to meet, hear, and party with Wilson... he is a really inspiring person.

dave

 

[Tyimo]

With ECL82 you'd need to change the feedback

How can I calculate the feedback?

Tyimo