Tube Preamp PSU Question - 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 18th January 2004, 07:05 AM   #1
diyAudio Moderator
 
JojoD818's Avatar
 
Join Date: Mar 2003
Location: searching...
Default Tube Preamp PSU Question

Hi everyone,

This may seem to be a regular stupid question but I still need to ask it to be sure. Thank you for understanding.

I found a schematic of a tube preamp in the web that uses 330-0-330 trafo, a 6X4 tube rectifier and CLC componets for a B+ of 255VDC.

My question is, can I replace this tube power supply with a descrete one? I mean using 2 regular rectifier diodes or a bridge diode? Do I follow the usual VDC = VAC X 1.4142 formula used in solid state? If I do, then I need a 180VAC trafo and a single bridge right?

This is my first of many tube projects, please help me.

Thank you very much,
JojoD
  Reply With Quote
Old 18th January 2004, 07:40 AM   #2
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Indeed, you are correct in your assumptions. Though i don't really understand how the 330v AC gets rectified down to 250v dc. Even allowing for heavy drops on the rectifiers and choke. Are you sure there are no additional resistors involved? Or is it choke input?
  Reply With Quote
Old 18th January 2004, 07:43 AM   #3
SHiFTY is offline SHiFTY  New Zealand
diyAudio Member
 
SHiFTY's Avatar
 
Join Date: Jul 2002
Location: New Zealand
Yep a 180 volt tranny with a diode bridge should be about right, or 180-0-180 with full wave diodes. Valves are pretty ok with differnt voltages, so 200-0-200 or even more would work just fine...

I usually find the multiplier ends up about 1.2 after a CLC filter BTW. 330-0-330 would end up at about 395V I think, is there a big resistor in the powr supply????

Also make sure your power tranny is rated for about double the current rating you intend to use, and put about a 0.1uF 3KV ceramic cap across the power transformer secondary to reduce noise.

A decent low R choke is good, maybe 10H or more at double your intended current...
  Reply With Quote
Old 18th January 2004, 01:18 PM   #4
diyAudio Moderator
 
JojoD818's Avatar
 
Join Date: Mar 2003
Location: searching...
Hi,

The preamp I am refering to is this http://diyparadise.com/preamptutorial.html

The choke I think is 595 ohms each? Could that be the cause for the voltage drop? Also, if I use a solid state psu, do I still need the chokes?

BTW, I just recently bought a cheap manual rewinding machine (the one with a turns counter) for use on passive crossover coils, can I build my own chokes?

Thanks for your patience.

JojoD
  Reply With Quote
Old 18th January 2004, 01:37 PM   #5
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Well, it is choke input so you multiply the 330v by 0.9 and then subtract the drop across the rectifier. Replacing the 6X4 with anything sandbased won't do much favours to the sound but can still sound decent. You still need to reduce power supply ripple and here you have a choice - either build a simple emitter follower type regulator (or just cap multiplier) or start from a much higher voltage and use several RC filters in cascade. What cap values can you get?
  Reply With Quote
Old 18th January 2004, 01:48 PM   #6
arnoldc is offline arnoldc  Philippines
diyAudio Member
 
Join Date: Apr 2003
Location: Makati
Send a message via Yahoo to arnoldc
jojo, i use duncan's excellent psu designer to make all my psu. it allows both solid state and tube rectification. pretty accurate too.
  Reply With Quote
Old 18th January 2004, 03:40 PM   #7
diyAudio Moderator
 
JojoD818's Avatar
 
Join Date: Mar 2003
Location: searching...
arnoldc,

Thanks for the info.

analog_sa,

I already have 2 pieces of ELNA 100uf/400V caps and more smaller capacitance, high voltage caps soon to come. I also have several 330uf/200V caps but that's for a tube preamp project that requires +/-100V rails. I once thought that these caps are useless since I needed large caps for ss.

I also have several small discarded trafos that can be recycled and rewound with fresh magnet wires for filter chokes.

You also mentioned that I can use solid state regulators, capacitance multipliers which I have some experience on. So as in ss, psu design really affects much of the overall sound of tubes?

JojoD
  Reply With Quote
Old 18th January 2004, 04:23 PM   #8
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Quote:
So as in ss, psu design really affects much of the overall sound of tubes?
Probably more. Tube circuits generally provide very little PS rejection. IME, which likely differs from that of others, a vacuum or gas rectifier sounds better than any kind of fancy diode and choke regulation sounds better than valve regulation which in turn is preferable to SS regulation. 200uF is simply not enough to achieve acceptable level of ripple with an RC filter. Nor is it enough to give you reasonably good bass. Increase the capacitance and the bass also increases in quantity but generally suffers in quality. Keep low capacitance but include a choke or two and you get low ripple and excellent bass. Chokes are also not created equal; it's nearly as difficult to wind a great sounding PS choke as it is to make a plate choke. Core material, flux level and DC resistance all seem to play a significant role.

Most commercial tube audio does not use chokes though. Too heavy and expensive to be worth it . You generally see diode bridges, hundreds uF of capacitance and simple emitter-follower type regulators. In the more upmarket stuff you may see tube regulators and Jung-type opamp regulators. If it's good enough for them it will probably do well in a first project.

Good luck.
  Reply With Quote
Old 18th January 2004, 11:50 PM   #9
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Money no object PS:

Valve rectification into LCL filter, into series reg using valves followed by C, shunt reg using a valve or VRs followed by R loaded anode.

Variations on this theme are welcomed but this pretty much sums up my favourite recipe.

Cheers,
__________________
Frank
  Reply With Quote
Old 19th January 2004, 02:20 AM   #10
diyAudio Moderator
 
JojoD818's Avatar
 
Join Date: Mar 2003
Location: searching...
analog_sa,

Thank you for explaining the behaviour and effects of psu on tube circuits. As I suspected, it does affect the output and must be very careful in selecting components for that matter.

Frank,

Lovely recipe, unfortunately, valve rectifiers are so hard to find locally, I'll go ss on my psu just to try my hand on tubes and maybe later on a valve psu too.

JojoD
  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
Tube Preamp Hybrid new builder, lots of question! eexdm2 Tubes / Valves 5 1st April 2008 01:24 AM
Tube preamp question...also, chassis layout jim_vt Tubes / Valves 1 22nd January 2006 12:01 AM
tube preamp kit question (again?) monomonster Tubes / Valves 1 23rd September 2005 11:36 AM
'Tube' preamp bad for measurement mic? also Apex mic question morbo Multi-Way 10 23rd March 2005 10:19 AM
A Class Preamp schematic and tube amps question MtUmut Solid State 0 10th March 2004 09:30 PM


New To Site? Need Help?

All times are GMT. The time now is 12:17 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