Hrrrrmphhhff. PSU design error and how to cope with it - 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 28th September 2012, 01:19 PM   #1
diyAudio Member
 
Rundmaus's Avatar
 
Join Date: Aug 2005
Question Hrrrrmphhhff. PSU design error and how to cope with it

Hey there,

due to the idea of building a one-channel test setup for my amp, I made a design error I now have to cope with. Situation is as follows:

The PSU uses one custom-wound power transformer with separate windings for both channels, each channel gets its own GZ34 rectifier and filter chain.

Now, guess what does *not* exist twice on my carefully planned (and ordered/shipped) power transformer... Yes, right, the 5V winding for the rectifier heater. F**k!

As the GZ34 has its heater internally connected to the cathode, I have the following options:

a) Live with the fact that the rectifiers are paralleled. Stretching SOA to its absolute maximum, one GZ34 should be able to supply the whole B+ current of 250mA (at 480-0-480 into L-C-L-C) in case one of the rectifiers fails. So failure of one tube would lead to a detectable (protection circuit) sag in B+, not to the immediate destruction of the second rectifier.

b) Rewire the rectifiers with both anodes in parallel, so each of the GZ34 acts as a single diode in the full-wave rectifier. Now we're safely within current limits, and the failure of one rectifier leads to half-wave rectification with B+ sag and audible hum. BUT: Startup of the amp might be a little hum-my if both GZ34 don't come up exactly the same instant.

(c)) Not really an option: Use only GZ34 with the internal connection burned away intentionally

What do you guys think?

Andreas
  Reply With Quote
Old 28th September 2012, 01:24 PM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
(d) Buy a small toroid with two 5V windings, tuck it in a convenient spot in the chassis.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 28th September 2012, 01:36 PM   #3
diyAudio Member
 
Rundmaus's Avatar
 
Join Date: Aug 2005
SY,

due to a lot of ideas that came up quite late, I am slowly but definitely running out of convenient spots in the chassis

Your idea was the first that came to my mind, but I hoped I'd get around putting another lump of iron under the hood...

Andreas
  Reply With Quote
Old 28th September 2012, 01:51 PM   #4
diyAudio Member
 
Join Date: Apr 2006
Location: up north
Use ss diodes and the gz34 socket for some kind of delay tube for B+?
  Reply With Quote
Old 28th September 2012, 01:56 PM   #5
pointy is offline pointy  United Kingdom
diyAudio Member
 
pointy's Avatar
 
Join Date: Mar 2009
can you put windings over the transformer windings that you already have.

(not safe but could work!)
  Reply With Quote
Old 28th September 2012, 01:56 PM   #6
diyAudio Member
 
yagoolar's Avatar
 
Join Date: Oct 2004
Location: Mazowieckie, Jozefoslaw
Send a message via ICQ to yagoolar Send a message via Skype™ to yagoolar
Add another 5V winding to the trafo?
(Pointy was faster)
  Reply With Quote
Old 28th September 2012, 02:14 PM   #7
12E1 is offline 12E1  United Kingdom
diyAudio Member
 
12E1's Avatar
 
Join Date: May 2012
Location: Near Huntingdon, Cambridgeshire, UK
In my experience there are acoustic benefits in keeping the rectification and subsequent filters separate for the left and right channels. (I have that set up on my current amp.) It greatly helps channel separation.

The transformer that I have only had one 5V winding but it had a surplus 6.3V one, so I used that for the second rectifier with a resistor to drop the 1.3V (ideally 0.72ohms - I used two 1.5 ohm 5W wire-wound in parallel). The actual resistor dissipation is just over 2W in total.

If you don't have a spare 6.3V winding, don't be tempted to use one that feeds the other valves since it will be directly connected to +HT of course.

Other options are as already suggested.
  Reply With Quote
Old 28th September 2012, 03:56 PM   #8
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi!

If your heater winding is specced for enough current for two GZ34, you might be able to use two 6BY5 instead. They only need 1,6A. If your heater winding delivers a bit over voltage due to the lower load, this might be an option. They have no connection beween cathodes and heater

Best regards

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 28th September 2012, 04:08 PM   #9
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
If your two HT secondaries are identical then parallel them and feed two GZ34 in parallel. This like your option (b) except the anodes are arranged differently. Avoids hum problem during warm-up, but at the expense of GZ34 overloading during warm-up during the few seconds when only one may be hot enough to function. No worse than (a) though, and only for a few seconds.
  Reply With Quote
Old 28th September 2012, 06:17 PM   #10
wa2ise is offline wa2ise  United States
diyAudio Member
 
wa2ise's Avatar
 
Join Date: Apr 2005
Location: NJ
maybe you can make use of a 5V switching power supply to feed the 2nd rectifier. Or you could use TV set damper diodes, those have separate heaters and cathodes, and H-K voltage ratings that are pretty high. Problem with that is that damper diodes are just half wave.

Is the power transformer a toroid? If so You could add a winding easier than if it's a regular transformer.
__________________
  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
Marantz CD63 KI SIG, Error 12, Sled Error problem sisik Digital Source 1 9th November 2008 04:12 PM
Modifying CMOY to cope with switching power mattkosem Chip Amps 16 7th September 2008 11:26 PM
PSU Design help wildbill Power Supplies 3 17th March 2006 08:02 PM
I need a schematic for a tubed crossover that can cope with 10k load impedance?!? hifi Tubes / Valves 7 16th August 2004 08:26 PM
Whats worse, 1db error in response curve or a phase error of 6? primalsea Multi-Way 5 13th May 2003 02:24 AM


New To Site? Need Help?

All times are GMT. The time now is 02:25 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