Solid state rectifier for SE guitar amp (Vox AC4) - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 21st May 2010, 10:44 PM   #1
ddr is offline ddr  United States
diyAudio Member
Join Date: Nov 2009
Default Solid state rectifier for SE guitar amp (Vox AC4)

Hi Folks,
I would like to build an amp similar to the 1960's Vox AC4. I would like to use a solid state rectifier instead of a tube. I would also like to use two power supplies, one for 250VAC and one for 6.3VAC (I have several Triad N68X power supplies on hand which should give me 250VAC if I run 125VAC into the secondary and use the primary for B+).

Can someone check my plan? It looks correct in Duncan Amp's power supply designer, but I have never done something like this before:
Click the image to open in full size.

Here is the original showing B+ of 270V:
Click the image to open in full size.

Thanks for your help,
Attached Images
File Type: png 1N5401_Bridge.png (10.5 KB, 186 views)
File Type: png AC4_PowerSupply.png (55.3 KB, 189 views)
  Reply With Quote
Old 21st May 2010, 11:18 PM   #2
diyAudio Member
Join Date: Mar 2010
The only caveat is that the inrush current may be a bit much for the rectifier. Check the resistance of the winding and, if necessary, add a resistor to protect the diodes.
  Reply With Quote
Old 21st May 2010, 11:27 PM   #3
kevinkr is offline kevinkr  United States
diyAudio Moderator
kevinkr's Avatar
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I think the triad isolation transformer will work just fine as a step up doing as you propose. You also have the option of making a Graetz bridge which is a tube/ss hybrid rectifier if you want to.. (I probably would)

Most solid state rectifiers have pretty healthy inrush ratings so a 2 - 4A 800PIV bridge would work well by itself or as the negative half of a Graetz bridge with a 6CA4 or 6V4..

Note that a solid state bridge rectifier may produce 5 % - 10% more voltage than the 6V4 rectifier shown, you can fix this by adjusting the value of the 1K resistor shown in your schematic
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine

Last edited by kevinkr; 21st May 2010 at 11:31 PM.
  Reply With Quote
Old 22nd May 2010, 02:13 AM   #4
ddr is offline ddr  United States
diyAudio Member
Join Date: Nov 2009
Thanks! I will research inrush current and Graetz bridges before I get started. I appreciate you both looking at this for me.

Take it easy,
  Reply With Quote
Old 25th May 2010, 06:55 PM   #5
diyAudio Member
Join Date: May 2008
You should use diodes with a higher voltage rating. Usually diodes for bridge rectifiers should be rated for 1,25 x Upp. For 250 V that is 1,25 x 1,41 x 250 = 440 V. The 1N5404 in your schematic are rated 400 V. 1N5405 would be the correct choice, if you build the rectifier bridge from single diodes.
Of course you could also buy a complete bridge rectifier, which make things easier, reduces the possibility of mistakes and usually also comes cheaper, if you don't go the hybrid rectifier path.

Originally Posted by ddr View Post
I will research inrush current and Graetz bridges
Looking for Graetz bridges will turn up what looks like BR1 in your schematic. You will have more success looking for hybrid rectifiers as a special form of the Graetz bridge.
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 3rd June 2010, 01:04 PM   #6
diyAudio Member
Join Date: Jun 2010
I've used 1N4007 as the diodes or better in all my tubeamps - no problem .... BUT you might consider improving the hum in the circuit by adding a resistor in series with the bridge value between 1R5 and 47R, 5W to 10W. This way you're removing all the spikes generated from the rectifier and you get a circuit that behaves more like the tuberectifier + you can use bigger capacitors. Tube rectifiers generally have a max. capacitance of 40uF as "load" and that is a major reason why they aren't bigger in old amps + the price of those bigger back then. Increasing the capacitors tightens the sound too - not what everyone wants in a Guitar Tube Amp, but many do, so try.

Also important - If you use EL84 (A GREAT little output Pentode), they sound their best at a max no signal voltage of 340V between anode and cathode. I know that many new amps from otherwise good brands are using much higher voltage in order to get more output power - it works but the sound gets harsh.
  Reply With Quote
Old 4th June 2010, 01:09 PM   #7
ddr is offline ddr  United States
diyAudio Member
Join Date: Nov 2009
Thanks folks, I am going to place an order next week for caps and a filament transformer and get this built! Thanks again for all of the great advice, I am learning quite a bit by reading the forum.

Have a good one,
  Reply With Quote


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
Solid state guitar amp. help needed! pilt Instruments and Amps 8 17th April 2011 06:25 AM
Solid state guitar amp Itbmetal Instruments and Amps 8 18th May 2009 04:13 PM
Solid state 100W guitar amp darkfenriz Instruments and Amps 6 3rd May 2006 11:21 PM
vox ac4 tankenburgen Instruments and Amps 5 29th August 2005 11:37 PM
Solid state guitar amp bostjancek Instruments and Amps 9 16th August 2003 06:23 AM

New To Site? Need Help?

All times are GMT. The time now is 07:36 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2