DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 20 Jan 2019, 17:29

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 105 posts ]  Go to page Previous  1 ... 7, 8, 9, 10, 11  Next
Author Message
 Post subject: Re: My 6AS7 SE Project
PostPosted: 21 Nov 2017, 14:30 
Offline

Joined: 07 Feb 2017, 19:06
Posts: 48
Location: Canada
Looking forward to that....


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 18 Sep 2018, 06:34 
Offline

Joined: 13 Jan 2018, 21:33
Posts: 98
Location: australia
thehoj wrote:
mwhouston wrote:
Seeing you have so much room how about making this a true integrated amp and add a single stage tube preamp. Plenty of room. Go for it. You can still put PS one side and preampamp the other.


I'm kind of regretting not doing that now.. I already built the 4S in a nice neat great working enclosure.. lol.

I've just noticed that I have to order a few switches from Mouser.. Maybe I'll look at the enclosures.

If one were to integrate the 4S preamp, how would the circuit look?. Would the 4S preamp replace the front end of Hoj's amp? Could the 6sn7 version of the 4S preamp work here? Regards Woodo

_________________
John


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 18 Sep 2018, 18:16 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1521
Location: US Pacific Northwest
Woodo wrote:
If one were to integrate the 4S preamp, how would the circuit look?
Hmmm... ok, let's talk about the amp first. The power stage of this amp is cathode biased at ≈75v producing around 3W peak output power. So, to drive this stage we need a driver that first, can swing to +/- 75v peak and second, does not require an exorbitant amount of drive voltage to get there. So when I designed the amp I chose a high µ tube, used large load and coupling resistances, and biased it specifically to meet the swing requirement without undue distortion. The result was a stage with a gain of about 71v/v and very even swing characteristics. This means that this amplifier only requires about 75/71 or about 1.06v peak or ≈750mV RMS to produce full power. This design represents a total driver gain of 37dB.

So to integrate a 4S preamp your going to have to make some choices. Obviously, a 4S in front of the existing gain stage would result in severe overdrive in virtually all conditions. If you simply replaced the driver stage with one of the 4S preamps, you would likely not have the gain required to meet the drive requirements of the power stage. I think what I would recommend would be a modified approach.

I think I would replace the driver used here with a high bias and low gain stage to meet the swing requirements of the power stage. They I would put one of the 4S preamps in front of this with the volume control between the two signal stages. Then the 4S provides the desired tonal shaping, and the volume control moderates the resultant drive but still allows the power stage to go to full output. I have high bias driver designs for both 12AU7 and 6AS7 but they might need to be slightly tweaked for the lower B+ voltage. But overall this shouldn't be too difficult a task.

Does this make sense?

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 19 Sep 2018, 02:16 
Offline

Joined: 13 Jan 2018, 21:33
Posts: 98
Location: australia
thanks Matt it does. It sounds a worthwhile project to advance. Reading TheHoj and Marks comments on their experience with this valve is motivating.

_________________
John


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 24 Sep 2018, 16:46 
Offline

Joined: 13 Jan 2018, 21:33
Posts: 98
Location: australia
Suncalc wrote:
Well I just ordered the iron for a different version of this amp. I've always wanted to bias this tube higher with a larger load to help reduce distortion and help the power. Now that I have a driver that will easily drive highly biased low sensitivity triodes, I've moved the design point for the 6AS7 up to Vp=176.5v and Ip=66.5mA (Eco ≈ -80v). I've also increased the plate load to 2.5kΩ. This should be a nice warm amp which should excel at the classical, jazz, and easy listening genres.

I'll report back after I've done some prototyping early next year. :sing:

Hi Matt- have you reported back on this research in another thread?

_________________
John


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 24 Sep 2018, 18:15 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1521
Location: US Pacific Northwest
Woodo wrote:
Hi Matt- have you reported back on this research in another thread?
OH NO!!!!

I just realized that I used the 2.5kΩ outputs I ordered for a different amp without ever doing the prototyping of this amp. :blush: Now I need to order another pair of the 2.5kΩ outputs. Still have the intended power transformer and nice Edcor 7H choke, but no outputs.

Well, 6 more weeks of waiting. :bawling:

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 11 Nov 2018, 05:59 
Offline

Joined: 13 Jan 2018, 21:33
Posts: 98
Location: australia
Suncalc wrote:
Woodo wrote:
If one were to integrate the 4S preamp, how would the circuit look?

They I would put one of the 4S preamps in front of this with the volume control between the two signal stages. Then the 4S provides the desired tonal shaping, and the volume control moderates the resultant drive but still allows the power stage to go to full output. I have high bias driver designs for both 12AU7 and 6AS7 but they might need to be slightly tweaked for the lower B+ voltage. But overall this shouldn't be too difficult a task.
Matt, i’m not totally clear on which high bias design mentioned above. Do you mean the driver section from “the beast” 6336 project ? viewtopic.php?f=9&t=5896&p=50293&hilit=12au7#p50293

if so, would there be much change to the plate and cathode resistors you used to match the 6as7? I bought a few 6as7s and plan to look for some 12au7s and other bits and pieces if this is the way to go.

_________________
John


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 11 Nov 2018, 15:14 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1521
Location: US Pacific Northwest
John;
Woodo wrote:
Matt, i’m not totally clear on which high bias design mentioned above. Do you mean the driver section from “the beast” 6336 project ?
"The Beast" 6336 Dual SET Amplifier

if so, would there be much change to the plate and cathode resistors you used to match the 6as7?

Actually that is exactly what I mean. For starters, the basic redesigned 6AS7/6080 amp looks like this:
Attachment:
6AS7 Amp Schematic.jpg
This amp will have good sensitivity already. However, if one were to integrate a "4S Universal" preamp into this, I would recommend that it look like this:
Attachment:
4S to Amp Integration.jpg
This way you get the tonal shaping of the 4S but can regulate it's drive to keep from overdriving the amp. The 250kΩ input pot on the amp is the same as the voulme control on the 4S Universal.

I will warn you, such a setup will be VERY sensitive. You will have to be careful not to overdrive the whole chain by tempering the input signal. Just to reiterate, I personally am not a fan of integrated preamps and amplifiers. I build all my amplifiers for typical line level drive and then if I want any tonal shaping or signal conditioning, I build my preamps separately. This is just my personal preference. YMMV. :)

Does this make sense?


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 12 Nov 2018, 03:09 
Offline

Joined: 13 Jan 2018, 21:33
Posts: 98
Location: australia
Suncalc wrote:
John;
Woodo wrote:

I will warn you, such a setup will be VERY sensitive....Just to reiterate, I personally am not a fan of integrated preamps and amplifiers

Yes thank you Matt. Thought it might be cool to integrate the 4s given its devepment and popularity but accept your views on this in this situation. Look forward to putting together the revised 12au7/6as7 based circuit.

_________________
John


Top
 Profile  
 
 Post subject: Re: My 6AS7 SE Project
PostPosted: 15 Nov 2018, 01:58 
Offline

Joined: 13 Jan 2018, 21:33
Posts: 98
Location: australia
Matt, would the original power supply circuit still be appropriate including with the 1.5 H chokes.

_________________
John


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 105 posts ]  Go to page Previous  1 ... 7, 8, 9, 10, 11  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Exabot [Bot], Google [Bot], Google Adsense [Bot] and 22 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy