A 6SN7 direct coupled preamp & regulated supply for everyone's perusal. - Page 2 - 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 23rd March 2008, 04:07 PM   #11
G is offline G  United States
diyAudio Member
 
G's Avatar
 
Join Date: Apr 2002
Location: Belleville, IL.
If the winding has the ampacity to carry 100mA from either end of the winding to the center tap then it should have the ampacity to carry 100mA through the whole winding shouldn't it?
__________________
Gavin
  Reply With Quote
Old 23rd March 2008, 04:30 PM   #12
diyAudio Member
 
sorenj07's Avatar
 
Join Date: May 2006
The transformers' current ratings are for capacitor input. Choke input quite possibly would free up more current.

http://hammondmfg.com/pdf/5c007.pdf
  Reply With Quote
Old 23rd March 2008, 05:07 PM   #13
G is offline G  United States
diyAudio Member
 
G's Avatar
 
Join Date: Apr 2002
Location: Belleville, IL.
Quote:
Originally posted by sorenj07
The transformers' current ratings are for capacitor input. Choke input quite possibly would free up more current.

http://hammondmfg.com/pdf/5c007.pdf

Thanks for the link but I don't think more current needs to be freed up. The transformer is rated at 40VA. The filament winding accounts for 6.3 x 2 amps = 12.6VA, the HT winding accounts for 250 x .1 amps = 25VA. 12.6 + 25 = 37.5VA. If one half of the HT winding is rated for 100mA then the other half of the winding is also.
__________________
Gavin
  Reply With Quote
Old 23rd March 2008, 06:17 PM   #14
diyAudio Member
 
Join Date: Sep 2003
Cool project G!
If sticking to Hammond iron for this project. Will the standad Hammond chokes like eg. the Hammond 158M (10H@100mA) work in both choke and cap input mode, or will choke input dictate another type of choke?
__________________
Thanx!
  Reply With Quote
Old 23rd March 2008, 07:01 PM   #15
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Default Re: A 6SN7 direct coupled preamp & regulated supply for everyone's perusal.

Quote:
Originally posted by G
Hi all. I wanted some opinions and vetting of a preamp & supply. Here ya go:
Loadline

Not real good; not too bad. It's not my preference, and you can do considerably better in the THD dept. No idea how this will sound. If most of the estimated THD is h2, you may prefer that type of sonic colouration. If there's a considerable h3 or higher order harominc profile, then may be not so much.

If you really need all that gain, there's a better way to get it, and with considerably more linearity. Bootstrap Mod. The additional coupling capacitor can be a 0.47uF unit, and make it a good one, like an AuriCap.

This gives virtually CCS loading on the input stage, and a very shallow loadline that'll perform much better in the THD dept. The DC operation does not change. It gives a lower Zo, and doesn't cost as much in Vpp as does either an SRPP or a u-stage.

Definitely something to consider.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 23rd March 2008, 08:01 PM   #16
G is offline G  United States
diyAudio Member
 
G's Avatar
 
Join Date: Apr 2002
Location: Belleville, IL.
Quote:
Originally posted by bequerel
Cool project G!
If sticking to Hammond iron for this project. Will the standad Hammond chokes like eg. the Hammond 158M (10H@100mA) work in both choke and cap input mode, or will choke input dictate another type of choke?
Hi Bequerel. Thank you for the compliment but others will disagree with you. The choke in the supply is a Hammond 193B. I had a LOT of help with the supply calculations from Zigzagflux and I'm pretty sure that you will have to change either C1 or C2 if you change the choke to a 10H/100mA choke. Hopefully he will chime in and tell you what you need to change. I'm not the best one to direct questions to when it comes to power supply calculations, or any questions other than the most basic, when it comes to tube electronics. I am little more than a rank amatuer.
__________________
Gavin
  Reply With Quote
Old 23rd March 2008, 08:22 PM   #17
jane is offline jane  Norway
diyAudio Member
 
jane's Avatar
 
Join Date: Jul 2004
Location: Norway
Default Re: Re: A 6SN7 direct coupled preamp & regulated supply for everyone's perusal.

Quote:
Originally posted by Miles Prower
If you really need all that gain, there's a better way to get it, and with considerably more linearity. Bootstrap Mod. The additional coupling capacitor can be a 0.47uF unit, and make it a good one, like an AuriCap.

This gives virtually CCS loading on the input stage, and a very shallow loadline that'll perform much better in the THD dept. The DC operation does not change. It gives a lower Zo, and doesn't cost as much in Vpp as does either an SRPP or a u-stage.
Bootstrapping is a neat trick, but the output impedance of the CF will rise a bit due to positive feedback. The positive feedback depends on the plate resistor (15k) and rp of the tube in the input stage. Since the cathode resistor (800R) not is decoupled the apparent rp will be quite high which will increase the positive feedback and Zout.

Jan E Veiset
__________________
Life is hard - Then you die.
  Reply With Quote
Old 23rd March 2008, 08:23 PM   #18
G is offline G  United States
diyAudio Member
 
G's Avatar
 
Join Date: Apr 2002
Location: Belleville, IL.
Default Re: Re: A 6SN7 direct coupled preamp & regulated supply for everyone's perusal.

Quote:
Originally posted by Miles Prower


Loadline

Not real good; not too bad. It's not my preference, and you can do considerably better in the THD dept. No idea how this will sound. If most of the estimated THD is h2, you may prefer that type of sonic colouration. If there's a considerable h3 or higher order harominc profile, then may be not so much.

If you really need all that gain, there's a better way to get it, and with considerably more linearity. Bootstrap Mod. The additional coupling capacitor can be a 0.47uF unit, and make it a good one, like an AuriCap.

This gives virtually CCS loading on the input stage, and a very shallow loadline that'll perform much better in the THD dept. The DC operation does not change. It gives a lower Zo, and doesn't cost as much in Vpp as does either an SRPP or a u-stage.

Definitely something to consider.
Hi Miles. Thank you very much for posting a reply. Here is the story about this circuit. I don't think I really need all that gain but maybe you can tell me after I tell you where I am coming from. I have been planning to build a matching (chassis wise) preamp and amplifier for a while. I actually decided on the amp first. It is a 12B4A gain stage and a 12B4A output stage. The input stage will be choke loaded and so will have a gain of 5 or so and the output stage uses a output transformer with a 40H 5K load and I am assuming that it will also have a gain of 4 or 5. I could be wrong about the gain of the output stage, or the input stage for that matter, but that is the amp that I am going to use this preamp with. I do like a "warm sounding" preamp. I have been using a "Foreplay" clone for the last two years. I decided though that I wanted to use a better tube for a future preamp and so I "designed" the circuit that I have posted using a 6SN7. I kept the supply voltage low so that I could lift the heaters to 80 or 85 volts above ground, using a single filament winding, and still be within the 6SN7s heater positive to cathode rating of 100v. I would like to claim that I designed the power supply but that was all Zigzagflux. I merely decided that I wanted a regulated supply for this preamp. So, you see, I do need some gain but I doubt I will ever utilize all of the gain this circuit has to offer. I do, however, need the low zout that his type of circuit offers. The load that I will be driving with this preamp might be as low as 9K so I need a output Z lower than 1K. That is the long and short of it. I could just use a 50K resistor from the input of the preamp to the pot and cut the input voltage in half to lower the output of the preamp although I am not sure how that will impact the sound. Thoughts?
__________________
Gavin
  Reply With Quote
Old 23rd March 2008, 09:44 PM   #19
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Quote:
If the winding has the ampacity to carry 100mA from either end of the winding to the center tap then it should have the ampacity to carry 100mA through the whole winding shouldn't it?
I apologize, G! I misinterpreted the transformer rating from your schematic because I thought the rating was expressed in AC terms, not in terms of its ability to supply DC. I looked up the Hammond website and I now see that The Hammond spec for the 369AX says: "Secondary: High voltage designed for full wave C.T. use. See chart below (High voltage current is D.C. using C.T. Full Wave rectifier - capacitor input)."

So, Hammmond gives an AC rating for the voltage but a DC rating for the current! I guess this must mean that the 369AX gives 125 x 1.414 volts = 176v @ 100mA DC using a C-input filter. This is approximately equivalent to an AC rating of 125-0-125v @ 170mA RMS. (With C-input, you only get ~60% of the rated AC Current).

Using the full winding with a bridge rectifier, you get twice the AC voltage and half the current, which is 250v @ 85mA RMS. The choke-input filter in your schematic should be able to give a DC voltage = 0.9 x the RMS voltage @ approximatley the same current, i.e. 225v @ 85mA before regulation.

The reason you can only use half the rated current over the full secondary winding, BTW, is because with full wave CT rectification each half of the secondary works 50% of the time but with a bridge rectifier the whole winding works 100% of the time.
  Reply With Quote
Old 24th March 2008, 02:08 AM   #20
G is offline G  United States
diyAudio Member
 
G's Avatar
 
Join Date: Apr 2002
Location: Belleville, IL.
Quote:
Originally posted by ray_moth


I apologize, G! I misinterpreted the transformer rating from your schematic because I thought the rating was expressed in AC terms, not in terms of its ability to supply DC. I looked up the Hammond website and I now see that The Hammond spec for the 369AX says: "Secondary: High voltage designed for full wave C.T. use. See chart below (High voltage current is D.C. using C.T. Full Wave rectifier - capacitor input)."

So, Hammmond gives an AC rating for the voltage but a DC rating for the current! I guess this must mean that the 369AX gives 125 x 1.414 volts = 176v @ 100mA DC using a C-input filter. This is approximately equivalent to an AC rating of 125-0-125v @ 170mA RMS. (With C-input, you only get ~60% of the rated AC Current).

Using the full winding with a bridge rectifier, you get twice the AC voltage and half the current, which is 250v @ 85mA RMS. The choke-input filter in your schematic should be able to give a DC voltage = 0.9 x the RMS voltage @ approximatley the same current, i.e. 225v @ 85mA before regulation.

The reason you can only use half the rated current over the full secondary winding, BTW, is because with full wave CT rectification each half of the secondary works 50% of the time but with a bridge rectifier the whole winding works 100% of the time.
No need for a apology Ray. I, in my ignorance, did not fully understand what the specs were telling me. I still have a lot to learn. I know just enough to be dangerous. Thank you for the explaination and I'm glad that I can use the transformer if I do decide to go ahead with this design. That remains to be seen though.
__________________
Gavin
  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
capacitor coupled vs. direct coupled ouput hugobross Solid State 11 21st January 2011 01:56 AM
single endedtransformer coupled 6sn7 mic preamp gurpreet Tubes / Valves 3 15th February 2009 08:55 AM
6sn7 direct coupled and transformer coupled neazoi Tubes / Valves 3 23rd May 2008 03:30 PM
Regulated PowerSupply for Frank's 6SN7 Preamp Vidi Tubes / Valves 2 10th December 2006 12:23 AM
Can someone explain parafeed & direct coupled & a.c. coupled? mwmitchell Tubes / Valves 2 11th September 2002 01:10 PM


New To Site? Need Help?

All times are GMT. The time now is 03:16 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