Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

I'm looking for 6an8 (as V1) schematics
I'm looking for 6an8 (as V1) schematics
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th September 2012, 11:05 PM   #11
tricomp is offline tricomp  Denmark
diyAudio Member
 
Join Date: May 2004
Location: Jutland
You really do go a far way to hang someone out!
What I meant was that all other tubecircuits on the forum has been invented 60 years ago, not the thing about copy-rights!
Of course if you're set to pick a fight there's always a way...

I never took credit for inventing the circuit; I just modified it to suit my taste. Something everyone does, actually HAVE to do, ref. the 60 years above. I don't know if that's enough to claim a copy-right and I don't care. The (c) was just put there to deter commercial use, not to pick a fight.

If the circuit has a bad frequency response is just a matter of testing it, as I have built it already. Since I have a Scope and a LF-generator (ISO-TECH 6022 & TTi TG2000) I'll do just that. You may even be right and I have a chance to improve it. Not that listening to it suggest it's necessary.
As for amplification I can say it fits extremely well with a pair of 5687-CF driven 2C34 in AB2-PP with NFB.

Anyway, I think this subject should be taken to another thread as it's straying somewhat from the initial subject.
However, it may be interesting for Kagliostro and others to know precisely how well it performs regarding frequency response with and without NFB.

Too late today; I'll get back with measuring-results tomorrow.

rgds,

/tri-comp

Last edited by tricomp; 16th September 2012 at 11:08 PM.
  Reply With Quote
Old 17th September 2012, 06:33 AM   #12
Kagliostro is offline Kagliostro  Italy
diyAudio Member
 
Join Date: Dec 2008
Quote:
Anyway, I think this subject should be taken to another thread as it's straying somewhat from the initial subject
No, don't worry all is fine as is

K
  Reply With Quote
Old 17th September 2012, 06:57 PM   #13
artosalo is online now artosalo  Finland
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
Quote:
Originally Posted by tricomp View Post
This boot-strapped version is not so well known but I highly recommend it ...
/tri-comp
Below is the simulated plot of the frequency response of your circuit.

Click the image to open in full size.

As you see the gain is not as high as it shoud. Also the frequency response and the AC-balance at low frequencies is poor. The low gain is due to some 35 V andode voltage. Instead it should be above 100 V.

Next plot is after I modified your circuit:

Click the image to open in full size.


And here is the modified schematic: (free for all purposes including commercial use)


Click the image to open in full size.
  Reply With Quote
Old 17th September 2012, 08:05 PM   #14
tricomp is offline tricomp  Denmark
diyAudio Member
 
Join Date: May 2004
Location: Jutland
I didn't measure exact output and frequency response of this amplifier before, as it was built more than a year ago and the test-equipment I have now was acquired only a few months ago.
The amp is installed and in use every day and sounds extremely well on my B&W 685 speakers:
Freq. resp.: 49Hz ~ 50KHz, -6dB
Spl.: 88dB (2.83V/1m)

These are the measured data of the whole amp. on an 8R dummy-load.

First w/o NFB, 1Vpp Sinus input.
Volumepot. adjusted to 1Watt output (8Vpp/8R) at ref. 1KHz (Setting approx. 10o'Clock)
Flat Midrange response from 600Hz to 6KHz. (8Vpp)
Bass response from 600Hz even drop till 70Hz -6dB (4Vpp)
Sub-Bass response from 70Hz even drop till 20Hz -12dB (2Vpp)
From 6KHz even drop till 23KHz -6dB (4Vpp)

Now with NFB applied, 1Vpp Sinus input.
Volumepot. adjusted to 1Watt output (8Vpp/8R) at ref. 1KHz (Setting approx. 1o'Clock)
Flat Response from 80Hz to 24KHz (8Vpp)
Sub-Bass response from 80Hz to 40Hz very small, even drop (maybe -1~2dB) then accellerating even to -6dB at 10Hz (4Vpp)
Subsonic response from 24KHz to 38KHz flat except slowly peaking at 30KHz (+3dB).
Beyond 38KHz even drop till 57KHz -6dB (4Vpp)

About Gain/Sensitivity:
It is absolutely perfect with NFB applied. Volume at full throttle requires an input of 0,5Vpp for max. output at 1KHz.
About Frequency Response:
Please say where the data looks bad, because I can't really spot the problem.

rgds,

/tri-comp

Last edited by tricomp; 17th September 2012 at 08:15 PM.
  Reply With Quote
Old 17th September 2012, 08:23 PM   #15
artosalo is online now artosalo  Finland
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
When a good desing methods are used, then every part of the whole circuit should perform well and their performance should be optimized separately.
Not so that the bad frequency response of the voltage amp./phase splitter will be fixed with GNFB. You can see from your own circuit diagram that the bias of the 6AN8 pentode is badly wrong. The anode voltage is only 35 V, which is far too low. (pls. calculate).

Then the simulation shows that the outputs are unbalanced badly at bass frequencies. Why that should be tolerated when it can be perfectly balanced ?
This causes not only the drop at frequency response, but also severe distortion at bass end.

The reason why the sensitivity/gain is now perfect is that your circuit do not perform as planned. It's gain is only some 40 dB but it should be above 60 dB if the circuit worked as planned. In such case the sensitivity would be far different.
  Reply With Quote
Old 17th September 2012, 08:23 PM   #16
tricomp is offline tricomp  Denmark
diyAudio Member
 
Join Date: May 2004
Location: Jutland
OK, thanks for taking an interest.

I'll try your suggestions in time but now I'm a bit stressed with work.
It will be interesting to measure and listen to the outcome.

The Phase-inverter output can swing around 80Vpp g-to-g which of course if far above what's required here.

rgds,

/tri-comp
  Reply With Quote
Old 17th September 2012, 08:33 PM   #17
artosalo is online now artosalo  Finland
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
This Jeffery cathodyne is very complicated circuit and it's performance depends much about the indvidual tube and it's characteristics.
Actually it should be fine tuned for each (L+R) channel.
I really do not see the reason for such high gain and the complications this may cause.
An ordinary pentode driven cathodyne gives 46...50 dB gain which is just fine for most of the output tubes (in UL and pentode mode). There is still up to 20 dB spare gain for sufficient GNFB.

I have design and built a commercially manufactured PP amp with such pentode-cathodyne with soviet 6F12P and it works fine.

Click the image to open in full size.
  Reply With Quote
Old 17th September 2012, 09:41 PM   #18
artosalo is online now artosalo  Finland
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
This is the cathodyne circuit I have used:

Click the image to open in full size.

I prefer not to DC-couple voltage amplifier and phase splitter.
Both has optimum operating point which usually are not the same.
  Reply With Quote
Old 19th September 2012, 12:36 PM   #19
tricomp is offline tricomp  Denmark
diyAudio Member
 
Join Date: May 2004
Location: Jutland
The real reason why I didn't use the tested and proven circuit like yours is that I would like to experiment and do things way off the ordinary.
And that's only because not a lot of people did it before, not because 'ordinary' isn't good or even good enough.
To me the challenge is to have something out of the ordinary function well, for what it wasn't originally intended.
To my knowledge no-one did the output-section related to the above posted pre/inv-section. It's a 2C34 Push-Pull Class AB2 Cathode-Follower-driven stage with VVT-transformers. It sounds extremely well and it may even improve with your suggested modifications.
I would post the schematic but unfortunitely it's also marked with copyrights
The picture attached of the amp is mine and therefore no question about (c).

I agree with you calculations of Va ~ 40V of the input-pentode. I arrive at the same conclusion as Ik is close to 1mA. However, measuring the actual voltage with a DVM with an input-R of 10Mohm shows Va ~ 125V. Now, that can't be true, but the scope confirms it and reveals no self-ocsillation that might cause distorted readings. Any explanation?

One question: C6 you propose to be 10uF.
I have read somewhere that this cap. shouldn't be increased too much as it may result in a kind of low-frequency self-oscillation; a sort of motorboating perhaps. What's your view on this?

You did a VERY beautifull amplifier and I have no questions about it performing well if you say it does.

rgds,

/tri-comp
Attached Images
File Type: jpg 2C34_PP.jpg (51.4 KB, 45 views)

Last edited by tricomp; 19th September 2012 at 12:43 PM.
  Reply With Quote
Old 19th September 2012, 04:41 PM   #20
artosalo is online now artosalo  Finland
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
C6 is the boot-strap "pump" capacitor. As you see it is 100 nF at your schematic and the impedance/resistance which it supplies is some 35 kohms (250k paralell with 40 k).
This makes the -3 dB corner frequency about 45 Hz.
This in turn means that the impedance of the cathodyne's cathode section begins to increase below some 100 Hz and starts to approach the 40 k cathode resistor, while it should be 20kohms.
At the same time the impedance at the anode remains 20k and is not depending on the frequency. Therefore the two outputs get badly unbalanced below 100 Hz.

In my simulation C6 was 10 uF but I checked it again with 1 uF and this is sufficient value. The balance is good down to 15 Hz.

The possible unstability (motorboating) is depending on many other thing too, mostly how big GNFB is used.

You have done a real good looking amplifier.
  Reply With Quote

Reply


I'm looking for 6an8 (as V1) schematicsHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
TSSA V1.5 sonnya SITO Audio 8 18th June 2014 08:00 PM
6AN8 Triode connection + EL 84 PP Tobruk Tubes / Valves 3 2nd May 2007 03:42 AM
6AN8 tube question HugoR Tubes / Valves 3 3rd November 2005 02:40 AM


New To Site? Need Help?

All times are GMT. The time now is 03:31 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki