Hrrrrmphhhff. PSU design error and how to cope with it - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 28th September 2012, 12:19 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?

  Reply With Quote
Old 28th September 2012, 12:24 PM   #2
SY is offline SY  United States
diyAudio Moderator
SY's Avatar
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 2
(d) Buy a small toroid with two 5V windings, tuck it in a convenient spot in the chassis.
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
  Reply With Quote
Old 28th September 2012, 12:36 PM   #3
diyAudio Member
Rundmaus's Avatar
Join Date: Aug 2005

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...

  Reply With Quote
Old 28th September 2012, 12:51 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, 12:56 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, 12:56 PM   #6
diyAudio Member
yagoolar's Avatar
Join Date: Oct 2004
Location: Warsaw, PL
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, 01:14 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, 02:56 PM   #8
diyAudio Member
Vinylsavor's Avatar
Join Date: Feb 2002
Location: Lindau

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

  Reply With Quote
Old 28th September 2012, 03:08 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, 05:17 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


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 03:12 PM
Modifying CMOY to cope with switching power mattkosem Chip Amps 16 7th September 2008 10:26 PM
PSU Design help wildbill Power Supplies 3 17th March 2006 07:02 PM
I need a schematic for a tubed crossover that can cope with 10k load impedance?!? hifi Tubes / Valves 7 16th August 2004 07:26 PM
Whats worse, 1db error in response curve or a phase error of 6? primalsea Multi-Way 5 13th May 2003 01:24 AM

New To Site? Need Help?

All times are GMT. The time now is 12:15 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