help on ul transformer please

[Giaime]

Go push pull. In single ended you'll lose power handling and frequency response because of the saturation of the core. In SE from a trasformer like that you'll have saturation at 1 watt or near.

A pp of EL84: they sound better than 6L6 or 807. If they aren't matched, use cathode bias with separate cathode resistor, or fixed bias with indipendent control of the single tube.

Hope this helps...

 

[arex]

thank you Giaime !

 

[arex]

I have another question, however:

(Maybe a stupid one, I have only the transistors experience)

I started with the idea to make a ultralinear single ended. But I haven't found the good transformer for cheap.

Now I will do it push pull.

But, if possible, I wouldn't want to rennonce at the ultralinear configuration. The idea is nice for me.
In the datasheet of those transformers it is said: "ultralinear tap at 25%"- speaking about 8000-2000 ohms wirings. (Not at 43%). If I use the 6000-2000 ohms primaries I will obtain a 33% ratio, but I dont know if I can use it. So: an ultralinear tap at 25% or 33%- it will be an efficient one? (of course I could add another negative feed back if necesary).

Thanks again

 

[Giaime]

True ultralinear is specified at 43%: around 40 seems fine. A lower number means that the screen grid will recive less feedback, so the tube will act more as a pentode.

I think that's useless, since when you'll build it I will suggest you to try in pure triode mode and you'll be so amazed that you'll forgot ultralinear... Really. Go for triode mode: you can even parallel tubes to get more power. If you have 8 EL84, you can make a push pull parallel... 4 per channel.

 

[Geek]

Now I am looking for output transformers. (they must be cheap). I found this one: http://store.triodestore.com/tf65wscta48o.html

.....at lowest note on a lead guitar (approx 80 Hz), this transformer can pass 50 watts or more.

Hehehehe, for about 5 seconds

sorry; schematic:

8 watts from a 6L6 in UL is a pipe-dream. Try 2, clean (but what a sweet 2 it will be!)

 

[SY]

The optimal tap percentage in Ultralinear depends on the tube, the trnasformer impedance, and the design goal. In their patents and early papers, Hafler and Keroes showed some very interesting graphs which beautifully illustrate the tradeoffs.

To make a long story short, a 20-25% tap will give you higher power but higher distortion than a 43% tap.

 

[arex]

Well, I wasn't too carefull when I readed that. I thought it was a se one. they propose themself a schematic:

but I didn't see it. In any case those AUDAX transformers seems to be "true" transformers by comparison with those fender-like, and with hammond too. The only think I don't like is that they dont have bell ends. (I'm not sure on the word).
The schematic I sended first time is a comercial amplifier, made by chimera labs. then I think the 8W of power was true.

I cant use 4 x 6L6 because I dont have them. I will try the push pull of el84 triodes. It seems to the best alternative to ultralinear.

If you know such a verified schematic (EL84 push pull in triode mode) could you post it please?

Thanks to all

 

[arex]

SY:

"The optimal tap percentage in Ultralinear depends on the tube, the trnasformer impedance, and the design goal. In their patents and early papers, Hafler and Keroes showed some very interesting graphs which beautifully illustrate the tradeoffs.

To make a long story short, a 20-25% tap will give you higher power but higher distortion than a 43% tap".

I think you are wright (with my small knowlege). I could use the 33% version too and another feedback. But I don't know if there are not others conditions to respect. The direction of wiring for example. Or the manner to alternate the wirigs. (sorry for my english. Hope you will understand).

 

[SY]

Let me see if I can scan one of Hafler's charts and get it posted. "Fair use."

edit: here's a link to the relevant chart

http://www.tubecad.com/Classic_Articles/page4.html

 

[arex]

You mean that I can use any ratio between 20% and 100% ?
(I dont know if I really understood ) . the best case will be about 50%. 10-15 watt of power will be enough.What tube did they use for V1 and V2?

I must read the whole paper. Thanks!