Real bass amps have tubes semiconductors are musical director trainees - Page 3 - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 6th April 2012, 08:36 AM   #21
diyAudio Member
 
Join Date: Oct 2011
Location: Tauberbischofsheim, Germany
Quote:
Originally Posted by Tony View Post
the 4D32 uses the same sockets as 839B, 832A, and 6C33....
Ok, Tony, thanks!

We call these sockets Septar on our side of the Atlantic, and yes, they're still available...

Another point: An output power of about 120 watts can also be expected from a pair of 6KG6A/EL519/40KG6A/PL519 tubes, running at about 420 volts and driving a load of about 1400 ohms. A pair of Circlotron monoblocks I've built about ten years ago generates even more: 144 watts right before clipping from two PL519s, running at 480 volts, into a load of 400 ohms (that equals 1600 ohms at a common PP design).

Best regards!
  Reply With Quote
Old 22nd July 2012, 03:19 PM   #22
Funker is offline Funker  Germany
diyAudio Member
 
Join Date: Feb 2009
Location: Hamburg, Germany
Hi All,
I recently made a breadbord Power amp for some examitations, especially with the grid currents. To estabish the facility for an individual idle setup for each valve, it is neccessary to use an separate drive valve for each opt valve.

I use six 12B4 valves which I had between my odds and ends. A widely makeshift power supply deliver the different voltages as there are 12.6V @ 6.5 Amp for the GU50 and 12B4, 6.3V @ 0.6A for the 12AT 7 and the 12 AU7, -160V g1 Voltage, + 250V g2, +400V input/phase split/ driver and +900V plate via variac.

The opt is also homebrew. It is a SE150a split tape core rpp 2,2k / 400W, 35 Hz/-3dB.

Some values in the circuit diagram has slightly changed while working on the amp.
The results of the last test delivers 440W into 4 Ohms ,the plate voltage drops down to 840V. The THD is 6% , 1 kHz
The grids of the op valve driven up to 20V peak. The idle current is set to 35mA. The input for full blast is 500mV. In this setup I feed the grids and screens via lab power supplies, not to see on the piccs.

Some suggestions for improvements and comments & crits are welcome.

73
Wolfgang
Here are some pics of the setup:
Attached Images
File Type: jpg DSCF0024.JPG (74.5 KB, 193 views)
File Type: jpg DSCF0026.JPG (74.8 KB, 193 views)
File Type: jpg DSCF0022.JPG (72.9 KB, 191 views)
File Type: jpg DSCF0012.JPG (73.7 KB, 176 views)
File Type: jpg A-1.JPG (77.1 KB, 175 views)
File Type: jpg Endstufe-2.JPG (214.1 KB, 112 views)
Attached Files
File Type: pdf Endstufe-2-1.pdf (42.3 KB, 49 views)
__________________
Ground your devices before they ground you

Last edited by Funker; 22nd July 2012 at 03:34 PM.
  Reply With Quote
Old 22nd July 2012, 07:54 PM   #23
diyAudio Member
 
Join Date: Jul 2007
Default Nice

Hi Funker.

Compliments: Nice circuit - I like the driver setup - pretty elaborate but I give you it does enables precise setting of each power tube bias in a much better way eliminating the need for selecting the tubes - which I have to.

The symmetical NFB is a nice touch - I probably would have used the sectons for cathode feedback on the power tubes instead. You decrease the effective damping factor by the loss in the OPT core not taking feedback directly from the speaker section but looking at the core size used it is probably negligible anyway.

I recently published a circuit using symmetrical feedback in a mixture of voltage and current feedback taking into account the MFB from the speaker coil itself. Works beautifully with large diameter woofers. Food for thought, maybe?
  Reply With Quote
Old 26th July 2012, 07:50 PM   #24
Funker is offline Funker  Germany
diyAudio Member
 
Join Date: Feb 2009
Location: Hamburg, Germany
Quote:
Originally Posted by thebasher View Post
Hi Funker.

Compliments: Nice circuit - I like the driver setup - pretty elaborate but I give you it does enables precise setting of each power tube bias in a much better way eliminating the need for selecting the tubes - which I have to.

The symmetical NFB is a nice touch - I probably would have used the sectons for cathode feedback on the power tubes instead. You decrease the effective damping factor by the loss in the OPT core not taking feedback directly from the speaker section but looking at the core size used it is probably negligible anyway.

I recently published a circuit using symmetrical feedback in a mixture of voltage and current feedback taking into account the MFB from the speaker coil itself. Works beautifully with large diameter woofers. Food for thought, maybe?
Hi thebasher,

due to grid current drive , there are a great amount of THD at high output levels. The tight coupled balanced nfb reduce these amount of THD drastically.
At my first considerations I would leave the output floated. But now my decision is to establish a second nfb from the speaker terminals to kathode of the input valve.
Another change is alredy done , I inserted a adiddional stage with a 6CG7between the 12AU7 and the six 12B4. The the gain of the 12AU7 is lowered by increasing the both kath. and plate resistors . The additional stage extend the maximum output swing from 50Vrms to amazing 80V rmas. So now my driver circuit got enough headroom without the risk to be overdriven before the output stage reach its maximum power.
The driver supply is now 500V. My experiences are still ongoing . My last test bringing 450W with 4% THD. The frequency range is from 30-15000Hz at Full power and 20-20000Hz with -3dB at the bandlimits. The grids are positve driven up to +20V peak.
Here are the latest schematic.

73
Wolfgang
DF6ZC

Edit.
There is no way to put a better schematic quality into this post. I tried pdf but the programm say to much data. The original schematic is drawn with S-plan!
Attached Images
File Type: jpg Endstufe-2-2.JPG (214.4 KB, 111 views)
__________________
Ground your devices before they ground you

Last edited by Funker; 26th July 2012 at 07:54 PM. Reason: schematic quality
  Reply With Quote
Old 26th July 2012, 11:44 PM   #25
diyAudio Member
 
Join Date: Jul 2007
Default Voltage + Current NFB

Hi Funker.
Here is the circuit I was talking about. It is basically a balanced/symmetrical amplifier from in- to output, not unlike your circuit.
What is interesting here is the 0.47 ohms resistor(R25) in series with the OPT secondary. You will probably say, that I am deteriorating the damping factor and to a certain extent it is true - but what I am really accomplishing here is producing a signal, which reflects the current of the counter EMF from the movement of the speaker coil - in other words: Motional feedback compensating for the erratic overshoots of the woofer cone.

Philips applied the principle in the late 1960's in a small two-way speaker with two built-in power amps and electronic cross-over. The woofer was a special design with two voice coils where the second voice coil provided the feedback signal.

The principle was called MFB or Motional Feed Back but never succeeded commercially since the units were quite expensive. They sounded very, very good for their size. I had a pair I regretfully departed with.

I have adapted the principle here using standard speakers and components, but dual voice coil woofers are available and might be considered as a more effective way of obtaining a true feedback signal - but it will be a voltage feedback and not current.

You may want to experiment a bit with the value of R25. The WW pot R24 can to a certain extent be adjusted to maintain the proper AC balance in the differential input stage.

I really built this because today's woofers simply do not have the huge magnets and efficiency of speakers of the 50's and 60's and are thus susceptible to cone overshoot due to the relatively poor damping factor of tube amps.

Does it work? Oh yes. This particular design is used as a playback reference amplifier in my modest recording studio driving two Tannoy 15" 385 coaxial (or as they called them 'dual concentric') speakers. The output power is about 24W/channel - more than adequate for the Tannoys. I have some recordings made with two Neumann KM84's and a Nagra IVS reel-to-reel tape recorder and it sounds incredibly clean and natural (chamber music and choir). Digital recorders - eat your heart out.

The harmonic distortion is measured to be less than 0.1% at 20W at the power bandwidth at 40-15,000 Hz into an 8 ohms non-inductive load resistor. The 3rd harmonic is too low to register on my test gear.

However, if I use a speaker as a load the apparent distortion goes haywire according to the analyzer because of the current feedback signal:

The NFB current feedback is regarded by the analyzer as 3rd harmonic which it is not.

But subjectively it sounds good - very tight bass which was the whole point and clear high frequency reproduction totally without audible intermodulation as opposed to standard tube amps driving complex multi-unit speakers with crossovers and other complex loads.

The circuit will work with virtually any output tube. I have used it with 6BQ5/EL84, 6L6GC, EL34 and KT88. ?lenty of drive for any tube.
Attached Files
File Type: pdf motion_feedback_amp.pdf (30.4 KB, 65 views)
  Reply With Quote
Old 26th July 2012, 11:52 PM   #26
diyAudio Member
 
Join Date: Jul 2007
Funker - I forgot:
Vy73 2u2
OZ5AAA
  Reply With Quote
Old 27th July 2012, 04:31 AM   #27
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
Hi Funker,

can you give dimensions of your C-cores and how much the iron weighs? thanks....
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
  Reply With Quote
Old 27th July 2012, 03:22 PM   #28
Funker is offline Funker  Germany
diyAudio Member
 
Join Date: Feb 2009
Location: Hamburg, Germany
Quote:
Originally Posted by Tony View Post
Hi Funker,

can you give dimensions of your C-cores and how much the iron weighs? thanks....
Hi Tony,

The Transformer is a DIN standard C core , SE150a , weight is app. 3.3kg
it need app. 2.8 kg copper wire , the finished trafo with the mounting frame weights 6.5kg.

Here are the winding scheme:

73,
Wolfgang
Attached Images
File Type: jpg A-1.JPG (77.1 KB, 75 views)
File Type: jpg DSCF1567.JPG (717.4 KB, 55 views)
File Type: jpg A-Wickelschema-1.JPG (193.1 KB, 84 views)
__________________
Ground your devices before they ground you
  Reply With Quote
Old 27th July 2012, 08:24 PM   #29
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
wow, that looks smoooth

hmm, any reason not to split the clear tape before winding the thin wire ?
looks like it crumples a lot
it might not if cut in the middle
but whatever, it looks cool
  Reply With Quote
Old 28th July 2012, 12:55 AM   #30
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
Quote:
Originally Posted by Funker View Post
Hi Tony,

The Transformer is a DIN standard C core , SE150a , weight is app. 3.3kg
it need app. 2.8 kg copper wire , the finished trafo with the mounting frame weights 6.5kg.

Here are the winding scheme:

73,
Wolfgang

Hi Funker, gold info, thanks....
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
  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
Musical Fidelity X10-D - changing tubes problem gsrai Tubes / Valves 17 30th March 2013 10:14 PM
a real no-brainer question about 1/2 tubes cbutterworth Tubes / Valves 3 14th December 2007 01:06 AM
musical fidelity headphone amps lt cdr data Headphone Systems 0 22nd September 2006 12:57 PM
Suitability of transmitter tubes for musical amplifiers Svetlana Tubes / Valves 20 31st August 2006 03:18 AM
Real russian tubes anyone?? Magura Tubes / Valves 13 10th January 2004 12:52 PM


New To Site? Need Help?

All times are GMT. The time now is 05:08 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