Help substituting power transformer. - 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
Reply
 
Thread Tools Search this Thread
Old 9th July 2016, 04:35 PM   #1
xephon is offline xephon  Japan
diyAudio Member
 
Join Date: Aug 2005
Default Help substituting power transformer.

I'm currently collecting all the parts for a tube amp build and I am a little stuck with sourcing a power transformer.

The design calls for a transformer with the following specs.

400 - 0 - 400v @ 340mA
0 - 5v @ 4A
0 - 6.3v @ 5A


Now, I have found a transformer with the following specs here in Akihabara, Japan:

0 - 350 - 400v @ 500mA
0 - 350 - 400v @ 500mA
0 - 5v @ 3A
0 - 6.3v @ 3A
0 - 6.3v @ 5A
0 - 6.3v @ 5A

I was thinking of tying the two high voltage secondaries together to get my 400 - 0 - 400, then maybe paralleling the two 6.3v @ 5A together for a 10A output just because.

My concern though is that the 5v is only 3A, not 4A as specified in the schematics. I'm thinking that they might just be specifying what was back then an 'off the shelf' transformer, so there might be some leeway?
I'm hoping this transformer will be ok otherwise it looks like I'll have to get a custom one wound....


Can someone have a look through my schematic and the info and let me know if I can get away with 3A for the 5V output?
This is my first tube amp (but not my first amplifier rodeo by any means) so I'm still getting up to speed with this glowy glass stuff..




Below is The original article with all the info, plus my slightly modified and redrawn schematic.
Attached Images
File Type: png Electronics-World-1961-03 pg29.png (486.7 KB, 153 views)
File Type: jpg Electronics-World-1961-03 pg30.jpg (579.7 KB, 151 views)
File Type: png Electronics-World-1961-03 pg31.png (669.4 KB, 150 views)
File Type: png Electronics-World-1961-03 pg32.png (551.2 KB, 141 views)
File Type: png Electronics-World-1961-03 pg85.png (240.5 KB, 131 views)
Attached Files
File Type: pdf Tube-Amp Schematic.pdf (153.4 KB, 30 views)
  Reply With Quote
Old 9th July 2016, 04:58 PM   #2
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
One GZ34 draws 1.9A heater current. At a push 4A will just cover it but for reliability I would use 5A as per the original design.
On your schematic link, what is the point of using silicon rectifiers in series with your valve rectifiers? It makes no sense.
__________________
Support for Fender, Marshall and all Valve Equipment including Audio Innovations, Quad and Leak. www.jonsnell.co.uk

Last edited by JonSnell Electronic; 9th July 2016 at 05:01 PM.
  Reply With Quote
Old 9th July 2016, 05:44 PM   #3
Hi_Q is offline Hi_Q  England
diyAudio Member
 
Hi_Q's Avatar
 
Join Date: Oct 2007
How about wiring the 5V 3A winding in series with the 6.3V 3A winding to give you 11.3V at 3A. Then wire the GZ34 heaters in series (keeping cathode connected pins together) and feeding them with the 11.3V via something like a 0.68 Ohm 7W WW resistor? The combined two in series will draw 1.9A instead of 3.8 Amps and the excess 1.3V will be dropped in the resistor which will dissipate just under 2.5 Watts. I believe the diodes have the task of producing the negative fixed bias supply so keep them in! Oh! Just seen your added schematic, yes I agree about the superfluous diodes on the anodes, the GZ34 has a PIV of 1500V but if you want to add something here then perhaps 100 Ohm series limiting resistors though usually the transformer winding resistance would somewhat provide this.

Last edited by Hi_Q; 9th July 2016 at 05:54 PM.
  Reply With Quote
Old 9th July 2016, 05:49 PM   #4
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Quote:
Originally Posted by xephon View Post
Can someone have a look through my schematic and the info and let me know if I can get away with 3A for the 5V output?.
The first quick answer is no. GZ34 rectifier filaments require 2 amps each and you only have 3 to work with. However, depending on the transformer you have, you may be able to push the rating because the other windings will be not loaded all that much. It really is a matter of heat dissipation.

An option could be to use one of the 6.3 volt windings for the two GZ34s with a suitable dropping resistor. Then use the other 6.3 volt winding for all the other tubes. Five amperes is sufficient to power them all. (7591s need 0.8 amperes each) Or you could parallel the other 6.3 volt windings. (5A & 3A)

A second option would be to purchase a separate 5 volt transformer with enough amperage to cover both rectifiers.

Further, a single GZ34 tube can supply enough current to power both channels using 7591 output tubes as evidenced by many commercial amplifiers from Fisher, HH Scott and lots of others.

Quote:
On your schematic link, what is the point of using silicon rectifiers in series with your valve rectifiers? It makes no sense.
The SS rectifiers I see are for the negative bias supplies.

Edit: Just seen the added schematic also. Diodes in series with the tube is a fairly new trick to help protect the poor current production tubes from China. (Like the JJs) Also in this diagram from the early 60's C21 & C22 are 150ufd each. Way to much for today's poor quality rectifier tubes.
__________________
1944: 18 year olds storm the beach of Normandy into almost certain death.
2016: 18 year olds need a safe place because words hurt their feelings.

Last edited by HollowState; 9th July 2016 at 06:17 PM.
  Reply With Quote
Old 9th July 2016, 08:31 PM   #5
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
Diodes in series with the tube is a fairly new trick to help protect the poor current production tubes
The series diode tweak shores the PIV weakness of the Sovtek 5AR4 up, nicely. Except for the PIV weakness, the Sovtek 5AR4 is good.

I can't comment (true/false) about the claim stating that a little extra service can be squeezed out of well used OS 5AR4s, by installing the tweak.

On general principles, use quiet UF4007s, instead of noisy 1N4007s.
Attached Images
File Type: jpg SS Series Diode Tweak.jpg (106.0 KB, 35 views)
__________________
Eli D.

Last edited by Eli Duttman; 9th July 2016 at 08:32 PM. Reason: grammar
  Reply With Quote
Old 9th July 2016, 11:19 PM   #6
diyAudio Member
 
Join Date: Jul 2015
Location: gothenburg,sweden
Quote:
Originally Posted by xephon View Post
I'm currently collecting all the parts for a tube amp build and I am a little stuck with sourcing a power transformer.

The design calls for a transformer with the following specs.

400 - 0 - 400v @ 340mA
0 - 5v @ 4A
0 - 6.3v @ 5A


Now, I have found a transformer with the following specs here in Akihabara, Japan:

0 - 350 - 400v @ 500mA
0 - 350 - 400v @ 500mA
0 - 5v @ 3A
0 - 6.3v @ 3A
0 - 6.3v @ 5A
0 - 6.3v @ 5A

I was thinking of tying the two high voltage secondaries together to get my 400 - 0 - 400, then maybe paralleling the two 6.3v @ 5A together for a 10A output just because.

My concern though is that the 5v is only 3A, not 4A as specified in the schematics. I'm thinking that they might just be specifying what was back then an 'off the shelf' transformer, so there might be some leeway?
I'm hoping this transformer will be ok otherwise it looks like I'll have to get a custom one wound....


Can someone have a look through my schematic and the info and let me know if I can get away with 3A for the 5V output?
This is my first tube amp (but not my first amplifier rodeo by any means) so I'm still getting up to speed with this glowy glass stuff..




Below is The original article with all the info, plus my slightly modified and redrawn schematic.
DON't paralell the high voltage windings, any difference will cause destructive current.
Use one only, unless you can build 2 independent B+ circuits. And the
lack of 5V current is easily fixed : drop the tube rectifiers and use 1n4007 si-diodes.
__________________
My home is at www.tubular-well.se
  Reply With Quote
Old 9th July 2016, 11:24 PM   #7
diyAudio Member
 
Join Date: May 2005
Location: California
Quote:
Originally Posted by Hi_Q View Post
How about wiring the 5V 3A winding in series with the 6.3V 3A winding to give you 11.3V at 3A. Then wire the GZ34 heaters in series (keeping cathode connected pins together) and feeding them with the 11.3V via something like a 0.68 Ohm 7W WW resistor?
Pure genius... I like it!
  Reply With Quote
Old 9th July 2016, 11:27 PM   #8
diyAudio Member
 
Join Date: May 2005
Location: California
Quote:
Originally Posted by petertub View Post
DON't paralell the high voltage windings, any difference will cause destructive current.
Use one only, unless you can build 2 independent B+ circuits. And the
lack of 5V current is easily fixed : drop the tube rectifiers and use 1n4007 si-diodes.
He didn't state that he was going to parallel the HV secondaries. Maybe something got lost in translation. What he is saying about the HV windings is to connect them is phase, IN SERIES, which is acceptable and will solve his problem.
He was talking about paralleling the 6.3 windings, which is also OK.
  Reply With Quote
Old 9th July 2016, 11:44 PM   #9
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by petertub View Post
DON't paralell the high voltage windings, any difference will cause destructive current.
If either winding is longer than the other it will cause the primary to take lots of current.
I got caught out with that one on a SMPS. I didn't wind the two windings exactly the same length and the primary took masses of current and blew the fuse.
__________________
Murton-Pike Systems PCBCAD51 pcb design software. http://www.murtonpikesystems.co.uk http://www.pcbcad51.co.uk
  Reply With Quote
Old 10th July 2016, 01:09 AM   #10
Hi_Q is offline Hi_Q  England
diyAudio Member
 
Hi_Q's Avatar
 
Join Date: Oct 2007
Quote:
Originally Posted by HollowState View Post
Also in this diagram from the early 60's C21 & C22 are 150ufd each. Way to much for today's poor quality rectifier tubes.
The caps are wired in series to give an effective capacitance of 75uF at 700V.
This is still pushing the GZ34 which has a recommended max capacity of 50uF.
So reducing each capacitor to 100uF would appear to be better. I have no experience of modern built GZ34 so innocently taking the 1500V piv from Philips spec sheet.

Looking at current prices asked for USED GZ34's borders to me on some kind of insanity. I would gulp at those prices for NOS Mullards
This is probably the main reason for going for SS, I use them myself and just ditching the heaters you will be removing 20 watts of heat from the amp.
  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
Substituting potentiometers Captn Dave Parts 0 12th April 2011 12:46 AM
Help with Substituting Transistors Ermac Parts 9 1st August 2009 03:57 PM
substituting FETs elementx Solid State 6 5th December 2006 04:40 PM
Substituting PCM 1716...? Lucas_G Digital Source 2 28th September 2003 07:18 PM
substituting mosfets Petervg Solid State 10 31st October 2002 03:53 PM


New To Site? Need Help?

All times are GMT. The time now is 04:34 PM.


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
Wiki