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 May 2019, 22:37

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 23 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
PostPosted: 18 Jul 2009, 06:05 
Offline
Project Author
User avatar

Joined: 08 May 2009, 08:20
Posts: 918
Location: Duesseldorf, Germany
Hi Adam,

don't hurry ;-)

Designing and planning an tube amplifier (or other amps) is NOT done in a few days. There are many things to think about. Even when you got an "ready to go" schematic. As said - Mikaels KT88 is a good start. Don't make it more complicated. The suggestions for the circuit are not a "must have" but makes sense when you use the KTs with the 400V PSU. Plan to use the 5AR4 /GZ34 rectifier and to get the right transformer. As Gio said, you must go for the right current values within the specs from the tubes you go to use. With Mikaels schematic you have already all the values for the components. The PS from Alex is OK with the 5AR4 /GZ34 rectifier. With the 400V i would add the 47Ohm 2-5W resistors for an symetrical operation (see pic.). And also the symetrical operation for the tube heaters as the KT88 has an Uf/k limited to 250V. And - i would suggest to add a fuse between the KT88 anodes and the output transformer. If the power stage tube shortens between heater/cathode - gates the transformers are protected. Mikael uses an "Ultralinear" output transformer - that's fine!

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


Top
 Profile  
 
PostPosted: 18 Jul 2009, 17:29 
Offline
Project Author
User avatar

Joined: 08 May 2009, 08:20
Posts: 918
Location: Duesseldorf, Germany
Now - this is the way i would build it and WHY (for me personal):
Attachment:
KT88_pr_PS.JPG
Ups - The R5 also is 47R 2-5W.
As said - an splitted output for a wider soundstage. This improves the "Stereo" effect. (Both channels are not mixed too much through the PS when one channel pulls the others current. The splitters 47R can be increased up to 1K without many losses). Yes - it is useful because an amplifier is nothing other than a modulated supply.. So - why not supply both channels separately (as good as possible now)?! The MKPs build a bypass for further ammounts of ripple current and they help against oscillations from / to the PS. The resistors at the GZ are described before and the centre tap is to set Uf/k to ground. (This is Important above 250V on the KT88! see Datasheet). Hint - The symetrical connection can also be build without centre tap... (only two resistors needed)
Attachment:
KT88_pr_Input.JPG
This input keeps any DC away from the pre stage (clean input) and sets the input sensitivity to an mid ranged value / input. 470K is an tubeworld standard also used in high end circuits.
Attachment:
KT88_pr_KT.JPG
So - i always use to add bypass caps (MKP) to the cathode caps and the input coupling. OK - Why:
The KT88 project is not a simple and "normal" project. This is High End (Imho). If you want to spend the money for KT88 tubes and ultralinear output transformers, you can put one or two dollares more on it. The bypass cap at the KT gate is to get a finer and more detailed sound. The amplified signal from the 6N1P can reach the KT gate with better conditions. The signals that can't pass through the 0,22cap (0,22 is ok and recommended), as every cap has an charge / discharge time delay and cut off, simply can pass through the silvered mica (or equal small MKP cap). The same way is also good for the cathode cap. Maybe some people now would think why i added all the stuff. Ok - it doesn't make it more easy but it makes the amp more "high end". That are not much more components for more and better sound...
Also could be added: Fuses to the OTs, LAG network at the output and a basic resistor load to keep the OTs saturation (magnetic saturation) low. As said - could.

The basic schematic to build the amp still is the one from Mikael! The transformer is from Alex' schematic / circuit. (This site).

Now - that was my whole personal opinion to the schematics / circuit. The changes are used in many high end amps and are described in many articles.

Keep an eye on the things that are important! (Transformer, rectifier, power resistors...) Take a look on the KT and 6N1P datasheet. There you'll find the limiting values for the tubes.
(The limiting values also were included in my suggestions).
And - don't hurry with this project. It will take a lot of time to build a clean amp. The KT project is worth it.

Enough for now - I hope that was a little more help for you and not that confusing (my english is not the best...) ;-)


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


_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


Top
 Profile  
 
PostPosted: 19 Jul 2009, 10:02 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4577
Location: Winnipeg, CANADA
Thanks Tom. My preference would be to remove the input capacitor unless you know that your source has DC at the output. Most CD players and such should be free of DC. For the cathode bypass, it could be interesting to try a LM317HV as a CCS in place of the resistor and cap. You could also try a CCS on the preamp tube.

Adam, on your schematic you don't show a switch to go between triode and ultra-linear mode. You may want to add one in to give you a extra mode you can try on the amp
Cheers, Gio

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


Top
 Profile  
 
PostPosted: 20 Jul 2009, 15:00 
Offline

Joined: 15 Jul 2009, 15:59
Posts: 11
Location: Nashville, Tennessee, USA
OK I'm at work, but I had some free time so I thought I would update the schematic. I think if we are trying to make the best possible sound then I think I would like to place the cap on the input. What would be the negative to that? Lower input volume?


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



Top
 Profile  
 
PostPosted: 20 Jul 2009, 19:50 
Offline
Project Author
User avatar

Joined: 08 May 2009, 08:20
Posts: 918
Location: Duesseldorf, Germany
That's going to be fine ;-)

Gio, sure, that's right - as the source is free of DC the caps maybe are not necessary.
OK, that was my opinion - I love clean inputs. That's the point i meant before - planning takes a lot of time ;-)
Until now i've never tried or thought about CCS... OK - it is not something new, but nothing that i know well, to give some comments to this. For this, i've some articles to study lying around here - also high end related... From next saturday i'm 3 weeks at Holidays. I have planned to come further with some learnings / studys - and with finishing some projects in this three weeks :-)

OK - caps.
The positive side is, that it eliminates / blocks all incoming DC current to keep the input clean. That means that with any sources the input doesn't get DC that might alternate the operating points from the modulation gates of the 6N1P. The negative side is, if the cap is not calculated right (within regarding the input resistance), the low frequency cut off is too high, and the signal sinus delays through the whole circuit are getting worse. Only for example (not an calculated one..): If the low frequency cut off is set to 10Hz within using ,047uF the cut off will raise to 40Hz with using 1uF. Not that what is wanted... The volume from the input circuit stays the same as the cap let pass by the AC sinus with nearly (not worth to think about) no resistance. But - the cap delays the AC sinus signal wave and that delay goes through the whole amp. In the original schematis from Alex / Mikael already are two 0,22uF caps engaged. So - changing the value for the input would not match the coupling caps from the KT88 input...
The input caps should not be electrolytic caps. I would replace them with HQ MKP caps (with no polarity). Such as the used Auri caps on Mikaels / Alex' schematic. http://www.audience-av.com/capacitors/a_description.php OMG - the price... Solen, Mundorf, Audyn or even Wima MKP10 (polypropylene types) work great. Mundorf caps i.e. are very popular - and maybe not that expensive.

One thing is sure: Smaller HQ capacities added to higher coupling capacities are a huge improvement for an amplifier.
And - adding the fuses to the OTs was a very good descision! That will be a bit more work to do but that really makes a sense.

OK - the Triode switch. Yep - it's on Alex' schematic and very very useful. Imho - an obvious thing to do.

Adam - some tips / hints to your schematic (that is a lot better now and very good!!!):
Rectifier: 5AR4 /GZ34. The rectifier resistors values should be 47 Ohm (47R). 47K is a bit too much ;-)
The MKP caps are always "non polarity" types.

I'll add a schematic for use with an xformers heater winding without centre tap soon and do some calculations for the resistors.

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


Top
 Profile  
 
PostPosted: 21 Jul 2009, 20:38 
Offline

Joined: 15 Jul 2009, 15:59
Posts: 11
Location: Nashville, Tennessee, USA
Alright, I've updated once again, I added the switch for ultra linear/triode operation, added part numbers for transformers, added a set of four inputs, and just overall cleaned the whole thing up. http://www.amcgough.com/C3.pdf. Let me know, I'm actually getting quite excited about this project. Again Thanks a ton for all your help Tom and Gio.

Adam


Top
 Profile  
 
PostPosted: 22 Jul 2009, 19:23 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4577
Location: Winnipeg, CANADA
Hi Adam,
I would do away with the fuse on the B+ after the audio output transformer. Also, a lot of the parts be a smaller voltage / power rating like the 47k resistor and 100uF cap on the preamp tube.
Cheers

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


Top
 Profile  
 
PostPosted: 22 Jul 2009, 19:30 
Offline
Project Author
User avatar

Joined: 08 May 2009, 08:20
Posts: 918
Location: Duesseldorf, Germany
That's a start. Adam - i can't believe that this is your first amp. Your work with AutoCAD is great!!!

OK - just some more little(!) things to say..

The 100N caps (PS output and cathode bypass) could be replaced with some other and cheaper caps like the Orange drops - http://www.tube-town.net/info/datenblaetter/capacitors/orangedrops-716p.pdf). There's no signal passing at this points and using "Auricaps" there, is a lot of wasted money... Vishay / Sprague or SBE Orange Drops 715-716 (or other good metalized polypropylene as mentioned before) are very OK and not that expensive. I guess the Auricaps are about 20 bucks? Let's save some money where it makes sense ;-) Auricaps or equal are a good choice for signal inputs / signal coupling.

The fuses are better placed at the OTs input (+) now. Sry - my fault - didn't think about the UL taps :? The mainpart for the fuse is to protect the OT windings - as said. That's going wrong if the UL tap carries all the current... The OTs are too expensive to take that risk. They should be rated a bit below the max. allowed OT current.
2W resistors for the PS out and the anodes is enough - even 1W.

With using the E88CC i would take a look on the datasheet. I'm not sure now(!), but i think the ECC has slightly other values (current draw)...
The heaters centre tap set to ground is very fine!!

I still got no chance to do some calculations and on saturday we're away for 2 weeks - but the values are good for a start!
I'll see if i'll get the chance on friday. The splitted output resistors could be increased a bit...

Imho - the whole thing really looks fine now and should be ready for takeoff!

Now, there is a lot of work comming. The next Step should be to get the schematic ready to release, which parts to use?, part lists, and so on... Hmm - and an enclosure. This also should be planned very well. There are a lot of traps for this too. Later...

Oh - Gio was faster ;-) OK - 160V ones is a bit much...

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


Top
 Profile  
 
PostPosted: 15 Aug 2009, 01:44 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 21:02
Posts: 85
Location: Philippines
Hi Adam,

Did you build the amp?

Am listening to mine now using Siemens EL34 and Sovtek 6n1p, the output tube triode strapped. Diana Krall's concert sounds excellent!


Top
 Profile  
 
PostPosted: 16 Aug 2009, 12:57 
Offline
Project Author
User avatar

Joined: 08 May 2009, 08:20
Posts: 918
Location: Duesseldorf, Germany
Hi again!

Are there Some news to the amp? Did you already start something?

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 23 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 14 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