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-   -   Set 6080/6as7 (http://www.diyaudio.com/forums/tubes-valves/37651-set-6080-6as7.html)

needtubes 12th July 2004 06:11 AM

Set 6080/6as7
 
Hi all-

I am once again heavily in a tube mood and searching for a simple, cheap amp to build... and perhaps might have finally found what I needed all along. Well, sort of...

The 6080/6AS7 is closely related to a 2A3... so, why not make a SET amp out of one 6AS7 and one driver tube (probably 6SL7)? I really need the project to be cheap... so using only two tubes for stereo operation really cuts down on the costs. I don't need a lot of power... 2-6W is it, really.

I have searched the forums, and found a thread by Joel regarding a Parafeed amp like this... but the chokes are WAY too large for me... I cannot spend that much. I need this to be as minimalistic as possible, while still sounding good.

Does anyone know of any links to any circuits like this? I found the Lilliput amp... and it looks really nice... but I was wondering if there were any similar to it, but maybe a tad better. It uses solid state rectification... and from what I understand 6AS7's like slow turn on supplies. Would this hurt the tube?

If someone can clarify anything, I would appreciate it. Thanks!!

Colt45 12th July 2004 06:29 AM

if you use a normal SE OPT, you'll need something in the 1k zone.. if i remember correctly. Which is kind of an off value, so it may be hard to find, unless you wind it.


I wouldnt worry about soft turn on - 6080s are tough ****ers, and pretty cheap too.


you could always just run 8 of them, OTL. but then you would have to spend the money you saved on the OPT on the big power transformers, extra tubes and some big caps. ;)

Sch3mat1c 12th July 2004 07:43 AM

You'll never get enough output from a 6SL7 to drive the 2 mu on that bastage. You need more supply volts or a choke loaded driver to do this one.

Or like Colt sez. :p

Tim

p_ete2003 12th July 2004 08:07 AM

Hi,

Check this Svetlana's page: http://www.svetlana.com/docs/tubeframe.html

http://www.svetlana.com/graphics/TB/No.26fig1.jpg
http://www.svetlana.com/graphics/TB/No.26fig2.jpg
There's a schema for 6AS7G.

If you would like to use only one tube/channel (+rectifier), check this page: http://digilander.libero.it/giunchif...ECL86amply.htm

I've built two ECL86-SE monoblocks with PCL86 tubes. The PCL86 is cheaper and easier to find. The only difference is the V they work (6,3/12V).

Best regards,
Pete

ThorstenL 12th July 2004 10:37 AM

Re: Set 6080/6as7
 
Konnichiwa,

Quote:

Originally posted by needtubes
The 6080/6AS7 is closely related to a 2A3...

It is? So a 2A3 is an indirectly framed grid valve? That's news to me.

Quote:

Originally posted by needtubes
so, why not make a SET amp out of one 6AS7 and one driver tube (probably 6SL7)?
Becuase it will not work too well?

Quote:

Originally posted by needtubes
I really need the project to be cheap... so using only two tubes for stereo operation really cuts down on the costs. I don't need a lot of power... 2-6W is it, really.
Something taht fits the bill of "cheap and easy" is a variation of the "Maurits" by Menno van der Veen. I commented on this here:

http://www.diyaudio.com/forums/showt...756#post351756

You should have come across this had you searched diyaudio for 6AS7 AND Amplifier.

Also, there is a Website with someones Experiences building a similar Amplifier to the Maurits, including the use of Mains Torroids as output transformer.

http://www.triodeguy.com/6as7_pp.htm

I would probably re-design the Amp by "bootstrapping" the driver from the opposite Anode (return the Anode resistor to the Anode of the halve of the 6AS7 not driven by this Valve and use a 5687/E182CC or ECC99 as driver and a 6072A or the like as driver. Anyway, plenty of scope optimising the driver circuit.

Sayonara

alk 12th July 2004 06:43 PM

Pcl 86's filaments volatage is 13V or 13.2v not 12v. Underfeeding the filaments may not be a good idea.

Cheers.

ThorstenL 12th July 2004 08:26 PM

Konnichiwa,

Quote:

Originally posted by alk
Pcl 86's filaments volatage is 13V or 13.2v not 12v. Underfeeding the filaments may not be a good idea.

Underfeeding filaments (within reason) is a most excellent idea, unless you operate Valves at absolute max cathode current (emission). As long as the continous cathode current is no more than around 50% rated maximum operating valves with the heater at the lower tolerance limit (-10% usually for heater/cathode construction valves) the lifespan of the Valve rises to 200 - 400% of that at nominal filament voltages. Plus, underheating sounds better with MOST Valves (but not all and not in all application).

Sayonara

alk 12th July 2004 09:13 PM

,
Quote:

Underfeeding filaments (within reason) is a most excellent idea, unless you operate Valves at absolute max cathode current (emission). As long as the continous cathode current is no more than around 50% rated maximum operating valves with the heater at the lower tolerance limit (-10% usually for heater/cathode construction valves) the lifespan of the Valve rises to 200 - 400% of that at nominal filament voltages. Plus, underheating sounds better with MOST Valves (but not all and not in all application).
I had read the contrary...guess too many ppl writing without knowing. ;)

I trust your knowledge though... this info will stay. Thanks.

Cheers!

ThorstenL 12th July 2004 09:24 PM

Konnichiwa,

Quote:

Originally posted by alk
I had read the contrary...guess too many ppl writing without knowing. ;)
I have studies both from the US and Europe from "the good olde days" which bear out the increase in lifespan. Note thatexcessive underheating can shorten life, overheating will DEFINITLY shorten life.

The 200 - 400% extended lifespan come froma Philips study.

All in all running valves conservative (try staying at or below 50% max rated anode dissipation and near 50% max rated anode current, also underheat at lower rated limited for heaters) can drastically extend valve life. A (power) Valve having 2,000-4,000 Hours expected live under the usual near max rating operation will hold usually four times as long (and longer) operated in ways I call "conservative". With small signal valves >40,000 Hours are easily possible.

With that even expensive NOS Valves are no real concern.

Sayonara

needtubes 12th July 2004 09:41 PM

I love building my own things... and have always wanted to build a tube amp, but don't want to deal with a really difficult design for my first amp. So, I just wanted something simple and cheap... and I figured I could use 1/2 of a 6AS7 for each channel and 1/2 of a driver.

However, I will be abandoning this project because like many of my other projects, I received less than friendly help from certain individuals. NO I do NOT know everything there is about tubes, which is why I was asking questions. I was basing what I said on things that I have heard or read... so oops if some things were incorrect.

There are a few friendly folks in the tube areas, and I apologize to those who are friendly and offer very nice help. However, everytime I post a topic asking for help I get met with some sort of hostility, and to be quite honest, I'd rather remain tube-less than have to put up with being made fun of for making a mistake that I was told to think was correct. I have never had a thread that ended well where I got the help I needed- otherwise I would have a tube amp right now and would have had one for some time.

So, I am leaving now, and shall NOT return to the tube forums again. I will seek help elsewhere...


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