ultra linear PP 6v6 kit (dynaco A-410)

[huggygood]

well, I will continue to share my observations and progress with great pleasure.
I have a dynaco MK4 kt66 clone also in progress

 

[Lingwendil]

it is also possible that the problem comes from my opt.
I know very well the brand of these, but I do not know this model, I just know they were pulled from a French amp el84m pp, expected as 2x17w.
on the other hand, it was done on specifications for the manufacturer of amp and do not appear in the catalog of the transformer manufacturer so I have no technical data.
when at my hp, I can tell you that they go down very low with my other amps.
and then we're here to learn so do it while having fun

Try some feedback. It helps loads on this design.

 

[huggygood]

I begin to understand the principle of adapting the feedback to the opt, I was missing a amp "suicide" to be able to have a little fun I do not master the oscilloscope very well, and as I learn alone, I often take a step forward and two steps back to check what I'm doing, so I do not move quickly

I started the amp with the new scheme and it's worse ... I think that, on the one hand I am too low in voltage b +, and that my output transformer are not adapted. I do a pose because it begins to annoy me , I build in parallel a MK4 which should relax me ...

I should receive a new pair of opt "supersonic W12" in a short time, I resume the wire at that time.

ok,I want to apologize for this kit and this diagram. when I had the opt that I used for this assembly, I had to find all the primary and secondary windings, then I changed all the son whose insulators were cooked and that's where I make a mistake, I misdirected my notes and I reversed two secondary windings (8 and 16 ohm) which means that it could not work because the scheme is based on his reaction. So I'm going to remake all that in order and redo tests.

 

[Francois G]

ok,I want to apologize for this kit and this diagram.

So I'm going to remake all that in order and redo tests.

No apologies needed! Good luck with the remake.

 

[huggygood]

it's the day and the night, it works much better ! I finally have bass and it does not break my ears. I'm still a little short in power supply (I miss 40vdc) but it works well. I have two other pairs of opt, I would do a test later after listening well.

very honestly, for the price, it works pretty well. I did not want to try other opt, but I tried several sets of tubes and for him it will be full Russian. what is surprising is that it works even better with a small buffer based on 6ak5 / ef95 (RSD in this case). for who wants a tube amp without constraint, he did not hesitate.

I must say that after several hours of listening with different speakers, I am really impressed by this little amp. I left the first set opt and frankly, we say what we want on the size of the iron, but in the end, a well done opt does not need to be big. As I am a bit low in B + (260Vdc) I made a test in triode connected and it is remarkable and perfectly silent even with a assembly breadboard.

to give an idea of the size of my opt, they are comparable to those of a Harman A300 or a magnavox console amp, except that it is a particular assembly, they are in a common box metal and drowned in tar (or something like that). they come from a French brand amp and are made by a manufacturer well known in France but I have no more data because they were tailor-made for the amp manufacturer and do not exist in the catalog of the manufacturer of transformers.

As soon as I have a moment, I will post all upgraded or modified schemas based on the dynaco a-410 that I could find on the net, there are a lot of things that I can understand in the different modifications, and others not.



opinions ?
i realy like too the Musical Machine of Poindexter and El Cheapo of Eli Dutman

 

[lavane]

I agree. I would not change anything. Although it could be better it is not bad as someone says. The Miller capacitance of the 6V6 with 43% UL is about 60 pF and each half of 6SL7 should work at about 0.9 mA. I can't see a problem, surely up to 25-30 KHz where the Hammond starts to give up.....
The paraphase is a better performing input/splitter stage than SE+concertina with tubes like the 6V6 and 6L6 in my experience despite its non-symmetrical look.

This amp will make a surprisingly good match with loudspeakers like the TABAQ.

I'm in the middle of building one of these amps right now. The UL should be at 23 to 25%.
What performance issues are there using a 40% UL? The OPT's I'm looking at do not have a 16 ohm tap so I would have to use the 8 ohm to tie the FB into. Would this be acceptable without having to adjust the cap in the FB circuit?
Thanks,
Paul

 

[lavane]

anyone?

 

[Alllensoncanon]

The UL should be at 23 to 25%. What performance issues are there using a 40% UL?

The OPT's I'm looking at do not have a 16 ohm tap so I would have to use the 8 ohm to tie the FB into. Would this be acceptable without having to adjust the cap in the FB circuit?

Changing the UL% will change the output tubes' V/I curve. You will require a different DC bias point to get the amp to an optimized operating level. The output impedance, bandwidth, gain, distortion characteristic and etc will also differ. That plus the global negative feedback changes (16R to 8R and the transformer itself, both the GNFB resistor and the compensation capacitor will need to recalculated and re-tune.

 

[lavane]

Changing the UL% will change the output tubes' V/I curve. You will require a different DC bias point to get the amp to an optimized operating level. The output impedance, bandwidth, gain, distortion characteristic and etc will also differ. That plus the global negative feedback changes (16R to 8R and the transformer itself, both the GNFB resistor and the compensation capacitor will need to recalculated and re-tune.

Thanks, that's what I thought. The original schematic shows a 1k resistor with a 1000of cap using the 16 ohm tap. I have some 620pf, 680pf, etc. I can try.