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

Role of paralleled EL34's in AES SixPac monoblocks
Role of paralleled EL34's in AES SixPac monoblocks
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 9th September 2018, 04:47 PM   #11
MrJackson is offline MrJackson  Romania
diyAudio Member
 
Join Date: Feb 2014
Location: Bucharest, Romania
Actually, the negative feedback switch is always off. The part about non-oscillating design was in the manual in the bias setting section, where it instructed the user to disconnect the speakers and connect the supplied bias measurement cable.
  Reply With Quote
Old 9th September 2018, 04:54 PM   #12
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by MrJackson View Post
I understand now that power’s not relative to the number of push pull pairs. I would be temped to try multiple configurations though as long as I don’t break anything. If it sounds bad, I can always revert.
I haven't looked at the schematics in detail but in general if you remove 2 pairs the remaining pair will work into 1/3 of the usual load. If one pair of EL34 works in class A into, say, 10K then for 3 pairs that load would be 3.3K. If you remove 2 pairs now the remaining pair will work into 3.3K. Heavy class AB operation. That will work but only in certain conditions which will be different. I see the quiescent current is 220 mA and appears to be the total for 6 tubes which is less than 40 mA per tube. With one pair the quiescent current should be in the region of 55-60 mA I GUESS otherwise distortion, especially a low and medium levels, will not be low.
Anyway if you objective is to roll tubes for making a final choice I don't think it is a good idea because the sound might be different between one pair and three pairs whiteout changing anything else.
  Reply With Quote
Old 9th September 2018, 05:04 PM   #13
MrJackson is offline MrJackson  Romania
diyAudio Member
 
Join Date: Feb 2014
Location: Bucharest, Romania
If possible, I'd always run it with a single pair... these amps get REALLY hot and it's not quite a pleasure in a hot summer. But I take it it's a bad idea.

As a side note, from Mr Carlson's findings in the video (when he adjusted the bias using a signal generator and a scope on the output), the bias can be set as low as 170mA on a full complement of tubes, so I guess 220 is a guideline for being in the safe zone to avoid crossover distortion.
  Reply With Quote
Old 9th September 2018, 05:41 PM   #14
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by MrJackson View Post
If possible, I'd always run it with a single pair... these amps get REALLY hot and it's not quite a pleasure in a hot summer. But I take it it's a bad idea.

As a side note, from Mr Carlson's findings in the video (when he adjusted the bias using a signal generator and a scope on the output), the bias can be set as low as 170mA on a full complement of tubes, so I guess 220 is a guideline for being in the safe zone to avoid crossover distortion.
I have being playing with a simple PP amp with EL34's in triode for the entire period of August holidays. It works fine with 3.3K but quiescent current is 60 mA per tube with 385V anode voltage I get very clean 17-18W. The sound with lower quiescent current is thin and I measure higher distortion. With 10K and 400V plate voltage the output power is less around 14W but it is better from every point of view. Actually with 3.3K it definitely needs some feedback to work best while with 10K it doesn't need any feedback.
So if you want to use one pair just change the output transformer using 3X primary load. That's just my advice.
  Reply With Quote
Old 10th September 2018, 03:58 AM   #15
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
If you take out four tubes, it won't be a "Six Pack".

Yes, you can probably cut from six to two *if* you change the load fro 8 ohms to 24 Ohms (not easy) and accept that you have 1/3rd maximum power.

If you do not change the load, the power is even less. 1/9th in simple theory. Since EL34 is a soft-curve pentode, maybe like 1/7th.

Since a "six pack" of EL34 is WAY more than many home hi-fi systems ever need, such reduced powers may still be ample.

If money is a concern, you maybe should get a smaller amplifier.
  Reply With Quote
Old 10th September 2018, 05:34 AM   #16
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
 
Join Date: Jun 2016
Wow!

I would not run that amp as it is designed, unless I did at least one of these things:

1. Purchase an IR thermometer (even an inexpensive one from Harbor Freight Tools).
Then carefully check the temperature of each one of the EL34 tubes.
There is No provision to balance the current of the 6 EL34 tubes.
One or more may be running very hot, and others very cool.
Just purchasing a "Matched set of 6", might not have current balance at the particular plate voltage and grid bias of your amp.
Just a 1V change in bias results in 11mA change in each tube's current; exact matching is paramount. Such high transconductance tubes are hard to really match with fixed bias.

2. Purchase a "Matched set of 6" that are Custom-Matched at the exact plate voltage, and at 220mA/6 (36.7mA), or a lower current such as 170mA/6 (29.3mA) that you will use in Your Amp.

And do not forget, if one or more tubes ages more quickly than the other tubes, they will not be balanced any more.

3. You could convert to individual self bias for each tube, but that requires 6 power resistors and 6 bypass caps for each channel. Probably no room for all of that.
The advantages would be:
A. Better matched currents, and better match as the tubes age.
B. A little less power dissipated in each tube, running cooler, and longer tube life.
The slight reduction in output power would not be noticed, you have plenty of power.

Note: The schematic shows these tubes to be wired in Triode Mode. Seems like a good thing to me.

Last edited by 6A3sUMMER; 10th September 2018 at 05:37 AM.
  Reply With Quote
Old 10th September 2018, 10:39 AM   #17
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by PRR View Post
If you do not change the load, the power is even less. 1/9th in simple theory. Since EL34 is a soft-curve pentode, maybe like 1/7th.
I disagree. It can be a bit more than 1/3 if you remove two pairs and adjust a little bit the bias without changing the load. The EL34 is triode connected here and I have played with a similar power stage for 2-3 week in August.
Using one pair biased at 400V/60mA per tube the only things that change going from 10K to 3.3K plate-to-plate are output power (class A and class AB, respectively) and distortion but not so much in terms of power. With 10K P=14W with less than 1% THD, with 3.3K P=18W at about 2% THD. The big difference is at low and medium level where the class A amplifier has got really low distortion in the region of 0.1-0.2% @1W while the class AB amp has already got 0.5% THD @1W. The latter needs some feedback to work best.
  Reply With Quote
Old 10th September 2018, 09:16 PM   #18
MrJackson is offline MrJackson  Romania
diyAudio Member
 
Join Date: Feb 2014
Location: Bucharest, Romania
Quote:
Originally Posted by PRR View Post
Since a "six pack" of EL34 is WAY more than many home hi-fi systems ever need, such reduced powers may still be ample.

If money is a concern, you maybe should get a smaller amplifier.
It's only 50W per channel... depending on your speakers, it might be barely enough. As for the money, yeah, you have a point... but only if we're speaking about hi-end tubes (you can't tell me $1000 is a small amount for a full tube completement). If we're talking about EH tubes, it's not a problem.

@6A3sUMMER: I haven't found any glaring issues with the matched tubes I've got so far. Sound is really good overall... but it does go to about 55ºC.

@45: I'll probably give it a shot at running with only 2 pairs per channel this weekend and see how it goes. I might be able to live with a higher THD (it's about .2% with no feedback)
  Reply With Quote
Old 11th September 2018, 02:33 AM   #19
Tajzmaj is offline Tajzmaj  Slovenia
diyAudio Member
 
Join Date: Mar 2011
Location: Ljubljana
It might help. Best regards.
TAD EL34B-STR Sextet :: TAD :: Tubes :: Banzai Music GmbH
  Reply With Quote
Old 11th September 2018, 02:54 AM   #20
Steve Morley is offline Steve Morley  Canada
diyAudio Member
 
Join Date: Jan 2015
Location: Georgian Bay
One simple thing we might be forgetting:

Removing 4 or even 2 tubes will mean a lighter load on the power transformer. This might result in the filament voltage getting well over 6.3 volts and shortening the lives of the remaining tubes in the amp.

Just sayin'
  Reply With Quote

Reply


Role of paralleled EL34's in AES SixPac monoblocksHide 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
what is the role of R4 and D1 in the schematic rhythmsandy Solid State 12 23rd February 2013 03:37 AM
role of cap in neg f.b. loop? farmerjack61 Solid State 8 9th October 2011 06:13 PM
Role of suprabaffle pathdoc2 Full Range 5 29th May 2010 07:14 AM
role of crossover aarono Multi-Way 2 24th March 2005 08:02 PM
Not new, but a new role planet10 Introductions 4 20th August 2002 10:46 PM


New To Site? Need Help?

All times are GMT. The time now is 05:06 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki