Push Pull DHT triode - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

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

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 8th January 2003, 11:28 AM   #1
diyAudio Member
 
Join Date: Nov 2002
Location: North Herts, UK
Default Push Pull DHT triode

I have re-worked my 2A3pp design after the excellent feedback on the diode bias version. In particular thanks to Brett, I have worked on the operating points for the 6C45 and the 2A3 and these are shown on the schematic. (please ignore the - sign on the 2A3 cathode volts they are +48 not -48)

I've shown this version with cathode bias as an alternative to the battery and diode bias of the previous design. I will build it both ways round to compare.

The design is heavily influenced by Lynn Olsen and Gary Dahls writings - as should be obvious by how deeply into class A the 6c45 is running - both Va and Ia are above the book max values

I guess the 2A3 looks under run for a Sovtek - but I agree with the comments that this valve sounds better closer to 45 operating conditions and it suits the 5K anode load to run slightly lower current.

The iron will be Sowter and Lundhal - probably one amp of each for a shoot out then order a second pair of the winner...

My experience with pp amps is that they can benefit from running slightly unbalanced so the iron is specified with some dc current capability. I usual still try to static balance the stages but I have experimented with up to 20% unbalanced dc and found that it can improve the sound and measure better... Not always but definitly sometimes....

Any comments gratefully received

Ciao

James
Attached Images
File Type: jpg 2a3pp - cathode bias amp.jpg (91.6 KB, 1085 views)
  Reply With Quote
Old 8th January 2003, 12:30 PM   #2
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default 2A3

Hi,

This looks perfect to me.
The 6C45 can take a lot so I won't lose sleep over that.

Here is were you surprise me...very few people know that:

Quote:
My experience with pp amps is that they can benefit from running slightly unbalanced so the iron is specified with some dc current capability.
I definitely agree with you here and FWIW a few died in the wool tube guys i know have confirmed these findings.
It often makes a huge difference.

Good luck building you obviously know your stuff,
__________________
Frank
  Reply With Quote
Old 8th January 2003, 02:43 PM   #3
diyAudio Member
 
Join Date: Nov 2002
Location: North Herts, UK
Default Old knowledge spoken by new heads....

Frank,

Many thanks for the kind words. I had good teachers... I was lucky enough to have a Valve amplifer tutor from about 8. My Dad was an electrician and caught me with my head in an old radio poking around. Realising he had very little chance of stopping my inquisitiveness he sought out an experienced valve man to educate me in the dangers and the pleasures of valve electronics. I had a wonderful time and learned how to design and build valve radios and amplifiers all through my teens. I didn't touch transistors until I reached twenty - then I spent 20 years wasting my time designing transistor amplifers. I'm now 46 and I have finally given up on silicon for audio. Some of us take a long time of banging our head against the wall before we realise it's not going to fall....

My audio valve previous has been with pentodes and beam tetrodes for output valves, sometimes connected as triodes, so all this DHT stuff is new to me - and it's wonderful!

I've designed and procurred studio audio equipment, sat on advisory panels for studio audio manufacturers as well as hifi and I can't believe I have gone back to where I started out! Valve amps and full range speakers!

ciao

James
  Reply With Quote
Old 8th January 2003, 05:06 PM   #4
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Very interesting. Anyone care to offer theories regarding why the unbalanced output sounds better. I didn't know it and will certainly try to put it to test.
If i had to offer an explanation it will most likely deal with the output iron enjoying the bias.


cheers

peter
  Reply With Quote
Old 8th January 2003, 05:13 PM   #5
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
On the up side:
How about the re-introduction of 2H?
(There could be something unnatural in a source having only discordant distortion).
Also, the transformer gets some standing bias.

On the down side:
The output valves' (carefully matched) curves no longer fit each other.

I'm just guessing.
  Reply With Quote
Old 8th January 2003, 07:21 PM   #6
diyAudio Member
 
Join Date: Nov 2002
Location: North Herts, UK
Default Why imperfection is better...

There are several factors working in favour of a mis-match pp pair sounding better than a matched pair (quiescent current match and mis-match) IMO.

1) we only static match the tubes and dynamically they will be mis-matched anyway - so there is a chance that the dc mis-match will result in a better dynamic match

2) If we know that we are mis-matching the pp pair then we allow for dc current in the OPT - the gap linearises the OPT considerably.

3) It increases even harmonic distortion...

4) It decreases odd harmonic distortion....

5) 3 & 4 together yield a better sounding distortion spectrum than a matched pp stage would produce... (this is much more important than 3 or 4 alone)

A good starting point for investigating this is

http://digilander.libero.it/paeng/on...P_Mismatch.htm

These were all known to the men who taught me. These men learnt their theory in the 40s and 50s and were 'expert' at Williamson style and Ultralinear designs. Interestingly they didn't rate the Williamson design that highly as it wasn't very good 'open loop' - they taught me that any amplifier was ultimately only as good as its open loop response. Global NFB was the icing on the cake - not the cake itself... I've found this to be true of all amplifier types.

I would love to hear some more reasons for this as well...

Ciao
James
  Reply With Quote
Old 8th January 2003, 09:00 PM   #7
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default MISMATCHING.

Hi,

James, you summ it up nicely.

The term "mismatching" is a bit of a misnomer here in that, as you describe it correctly, you rematch the output tubes dynamically.

We found this out accidentally...no idea this was documented at all.

Cheers,
__________________
Frank
  Reply With Quote
Old 8th January 2003, 11:14 PM   #8
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Push Pull DHT triode

Hi,

Quote:
I have re-worked my 2A3pp design after the excellent feedback on the diode bias version.
Nice Job. I designed something a little similar for a friend. There the 6S45 differential stage drives 300B's, direct coupled.

Click the image to open in full size.

Sounds rather good actually, especially with TJ "Mesh" Anode 300B's. Drawn BTW by Morgan "Valve Amplifers" Jones and Build by Jon "Electrostatic" Finlayson. As you can see, i had little at all to do with that Amp...

Sayonara
  Reply With Quote
Old 10th January 2003, 07:39 PM   #9
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Default Monkeys

Mmm,

Been thinking of some monkeying around myself.
Are the chokes "normal"?

Cheers,
  Reply With Quote
Old 10th January 2003, 11:10 PM   #10
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Monkeys

Hi,

Quote:


Been thinking of some monkeying around myself.
Are the chokes "normal"?

The ANode Load chokes are in fact vintage output transormers from and EL84 PP Amp, secondary unconnected. I suspect a custom made, super low capacitance unit with permalloy core would be better still, but decent EL84 PP OPT's can be found VERY cheaply....

Sayonara
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
EL34 in class AB2 triode mode push-pull? ray_moth Tubes / Valves 29 8th March 2009 07:34 PM
modify parallel push-pull EL84 to single push-pull chungtat Tubes / Valves 12 3rd November 2005 11:25 PM
Push pull dht triode with diode bias James D. Tubes / Valves 24 5th January 2003 08:19 AM
DHT triode push pull amplifier design James D. Tubes / Valves 2 5th December 2002 08:44 AM
Biasing Push Pull Triode amp into Class A G Tubes / Valves 11 4th November 2002 02:27 PM


New To Site? Need Help?

All times are GMT. The time now is 05:12 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2