#26 pre amp - Page 14 - 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 10th November 2009, 08:38 AM   #131
Arnulf is offline Arnulf  Europe
diyAudio Member
 
Join Date: Feb 2009
Quote:
Originally Posted by Rod Coleman View Post
So LT1084/6 or LM350 meet the functional requirements, provided your heatsink is big enough, but you have to listen to them to be sure.
@Richard and others with regards to above comment: I used a couple of LM350 (supposedly Fairchild part, purchased via Farnell) in a project recently and it was as if the tab on the back side was stamped out of a tuna can Any LM317 (in same TO-220 package) I came across has tab more than twice the thickness of that LM350 and there's no way it would get bent by merely looking at it the wrong way (unlike that of LM350). I have never seen such a flimsy tab on any TO-220 device.

The result was that regulator kept shutting down due to overheating because that thin tab couldn't take the heat away and thermal contact between the heatsink and the tab wasn't good enough. Higher datasheet rating aside, 1A filament doesn't require 3A-specced regulator so I wholeheartedly recommend you guys NOT to use LM350, at least not one coming from same stock. What good is that rating anyway if device keeps shutting down at lower dissipation than LM317 ?
  Reply With Quote
Old 10th November 2009, 09:39 AM   #132
CFT is offline CFT  United States
diyAudio Member
 
Join Date: Jul 2006
Location: Hong Kong
Hi Lars,

I am interested in putting together the parafeed circuit you posted on page 10.

Any follow up on it? And possibly a more complete circuit/ sim available?

Thanks!!
  Reply With Quote
Old 10th November 2009, 09:58 AM   #133
diyAudio Member
 
Join Date: May 2007
Hey Cheung,

Will mail you something within a few days with cascoded FET´s as you wished.
  Reply With Quote
Old 10th November 2009, 10:16 AM   #134
Richard is offline Richard  Australia
diyAudio Member
 
Join Date: Apr 2005
Location: Melbourne
Hi Rod,

Thank you once again for the excellent advice, I should be able to squeeze it into the preamp chassis.

Do you think it would be beneficial to mount all the parts for this circuit (except the big cap) in a small sealed aluminium diecast box (also using it as a heatsink) and have leads out for the tube filament and voltage in?

As for cathode resistor position, I’m using the centre tap of 2, 20ohm resistors. Looking at a lot of the data sheets I’m at a loss as to which filament pin is the +and the -. Can anyone enlighten me?

Arnulf, It’s a pity you may have a bad batch of LM350’s. I just measured the mounting tabs thickness of my Fairchild LM 350T at 1.34mm and the LT1086 at 1.26mm. Perhaps the T version is a bit more robust.

Cheers,

Rich
__________________
"A little learning is a dangerous thing"
  Reply With Quote
Old 10th November 2009, 10:36 AM   #135
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
Hi Rod,

Could you post a schematic just of the gyrator circuit? I'm not a star at reading solid state schematics...

I would be easier for me to see what the gyrator looks like, build that into my positive supply and build a ccs for the negative supply. Would that work?

Kind regards,
Bas

PS. for the ccs I am thinking of a cascoded IXTH20N50D.
  Reply With Quote
Old 10th November 2009, 10:45 AM   #136
diyAudio Member
 
Join Date: May 2007
Hey Rod,
Your simmed CCS/Gyrator is grounded. Should be floating shouldn´t it?
  Reply With Quote
Old 10th November 2009, 10:57 AM   #137
CFT is offline CFT  United States
diyAudio Member
 
Join Date: Jul 2006
Location: Hong Kong
Wow! excellent, thanks a lot Lars!!

Both of you and Rod have made my day today
  Reply With Quote
Old 10th November 2009, 11:41 AM   #138
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Quote:
Originally Posted by Bas Horneman View Post
Hi Rod,

Could you post a schematic just of the gyrator circuit? I'm not a star at reading solid state schematics...

I would be easier for me to see what the gyrator looks like, build that into my positive supply and build a ccs for the negative supply. Would that work?

Kind regards,
Bas

PS. for the ccs I am thinking of a cascoded IXTH20N50D.
Bas,

The gyrator is M1 plus R3/R4/C2 in the circuit I posted in this thread. That one is just an idea for those that don't like to build with bipolar transistors - I haven't tested it, although the simulation models just fine.

The schematic on this old thread:

New DHT heater

Has been tested and known to sound wonderful with 300Bs. The gyrator portion is Q1/T1 and the Rs/Cs around them.

I have updated this circuit a little, and will repost when I get a minute!

For sure, use the gyrator for the +ve, and CCS for negative.
  Reply With Quote
Old 10th November 2009, 11:43 AM   #139
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Quote:
Originally Posted by revintage View Post
Hey Rod,
Your simmed CCS/Gyrator is grounded. Should be floating shouldn´t it?
Lars, yes it should float compared to your B+ ground, but LTspice won't simulate without a ground. Think of the gnd symbol on this circuit as "0V(filament)".
  Reply With Quote
Old 10th November 2009, 11:46 AM   #140
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
Quote:
I have updated this circuit a little, and will repost when I get a minute!
Thanks!
  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



New To Site? Need Help?

All times are GMT. The time now is 04:25 PM.


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