6AS7G SE or P-P?

[Jerry garrcia]

Here you go.

I also have designed 6AS7G SE if you need.

A bit late but saw your schematic for the PP amp. Was a bit curious about the SE schematic. Care to share?

 

[woodo]

I built one of @Suncalc designs or at least an early draft at cascadeaudio.com. Look for purpleheart 12au7/6as7 set. I have a variation of his design of the silver dragon 300b set the thread of which is on diyaudioprojects.com both very nice listening. I play the 6as7 set most of the time due to a preference for it sound despite its lower power output.

 

[artosalo]

Was a bit curious about the SE schematic. Care to share?

 

[Jerry garrcia]

Will the single 6J38P function just as the driver so a separate preamp will need to be used? Also got this schematic.

 

[woodo]

purpleheart 12au7/6as7 set.

fyi: https://www.cascadetubes.com/the-6as7-purpleheart-set/

 

[artosalo]

Jerry, did you look the test results I attached?
There you can see, that the sensitivity is 0.7 Vrms to 9 W out, when 6 dB GNFB is used.

 

[Jerry garrcia]

Yes and thank you. Looking very promising and a simple enough circuit. My main concern is the pentode up front. Was hoping to be able to utilize all octal tubes if possible. Preferably with the same nice coke bottle appearance as the 6AS7G.
And did you test the two different output transformers in your schematic? Want to keep the cost as low as possible with still a decent sound since my better half is complaining a bit about spendings on different electronic components 🙂. Have a hard time to get rid of something I built and designed so have way to many guitar amps…
The PT must really be chunky to support two of those tubes in parallel SE stereo. About 600mA😬

 

[artosalo]

Was hoping to be able to utilize all octal tubes if possible.

6AC7 is high gain pentode with octal base. ( http://www.r-type.org/exhib/aaa0053.htm)

And did you test the two different output transformers in your schematic?

Yes, but I prefer this: (https://sklep.toroidy.pl/en_US/p/TTG-EL34PSE-Tube-output-UL-transformer-1,65kOhm-EL34-6L6-PSE/577)

The PT must really be chunky to support two of those tubes in parallel SE stereo. About 600mA

Not that much. The plate current of a 6AS7G is only 50 mA/triode halve, 200 mA for whole output stage.

 

[Jerry garrcia]

Thanks. In the tube data sheets they rate the plate currents to 125mA for each triode. http://www.r-type.org/pdfs/6as7g-1.pdf so that times four gives 500mA
Is it with your settings that gives it to 50mA?

 

[artosalo]

Is it with your settings that gives it to 50mA?

Operating point: Ua = 250 V, Ia = 50 mA is quite optimal. This makes 12.5 W plate dissipation, that is just within the max. rating.
Tube is at linear load line etc. Power output is high.
It is much more optimal than Ua = 100 V, Ia = 125 mA, (Pd = 12.5 W too)

 

[Jerry garrcia]

🤯. Sorry. A bit scared of a pentode up front. I really like the 6SJ7 in guitar amps but there is something that freaks me out. As I think I wrote I’m new to hifi but built many different guitar amps before. Need to learn the basics again I think.

 

[artosalo]

Also got this schematic.

That circuit has 6N13S as fixed biased. That is not recommended. The application note states as follows:

"Always use self bias; fixed bias must not be used."

 

[krca45]

Arto could You please show good picture of the regulator from schematic ( IRF820 + LM317 ) ?

Krca

 

[artosalo]

Here:

 

[hooman]

The schematic is very good. I bought a number of 6080 and I would like to hear it in hi-fi with a Rogers 3.5 speaker. Is the pushpole capable of 30 watts with a 6080 tube?

 

[artosalo]

Yes, two tubes (4 triodes) are needed and 400 V as +Ub.

 

[jhstewart9]

More than 20 yrs ago I got interested in solving the 6080 drive problem in audio amplifiers.
It looked to me the easy way out was already in full view in Electrovoice & McIntosh amps,
Simply bootstrapping the driver stage would do that. Why didn't anybody try that, so I did,
All of the experimental builds & EWB simulations were for 'Proof of Concept' purposes. Hardware was built in some cases.
So I've got a PP 6080 on the shelf, to run it I use a lab power supply. Something else is on the PP 5998 chassis now.
Much of the resulting information for the PP 6080 version was published in Glass Audio & Electronics World.
One of the simulations shows 6BQ7s in the front end differential amp. I've done this to let others know I'd had very good results
in a different build when these were stuffed into the 6SL7 & 6SN7 sockets with adapters. Something to think about.
Many people express concern about the use of positive FB in the driver stage. But ask anyone, how much +ve FB. And how did you get that number?
Nine out of 10 don't know or how to measure or calculate that number, Here is my calcs. I measured it as well, from 1.5 to 2 db is the range.👍

 

[jhstewart9]

When I was doing this work I wondered what PP 845s would do with a boot strapped driver.
The Sim looks like ~37W with a 10V input signal.

 

[Jerry garrcia]

Update. Got a hold of an hifi guy who also sold OT’s. He strongly discouraged me to go ahead with the 6AS7 project. Mainly since, with his experience time after time tried it, simply showed that the ratio good sound + cost of transformers was better with another tube. Like a triode strapped EL34 in a SE configuration has about half the price in parts and better sound. His subjective input 🤔

 

[piano3]

Voltage regulator tubes have their own particular quality when used for audio, possibly due to their ability to deliver current. I would not take too seriously the advice from a vendor. If he is unable to get get good results, then it is his skill which is lacking. You have the valves, why not just build Artosalo’s PP amp. It is bound to sound excellent. Actually 6AS7 is suitable to use with a cheap mains Toroid as OPT if you can accurately balance the currents on each side.