Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki 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

Power transformer (advise needed)
Power transformer (advise needed)
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 6th December 2017, 01:36 PM   #51
gabdx is offline gabdx  Canada
diyAudio Member
 
Join Date: Jan 2008
Calculating the proper type of power transformer is difficult even for experienced builders.

You need to purchase a transformer which is designed for your circuit and labeled to provide the voltage range you want for the type of rectification.

My advice: dual power transformers is very difficult to build and lot of noise and problems can occur. I could never complete an amplifier with 3 power transformers which integrated a dedicated pre-amp and 2 mono for power sections. The ground path always carried hum no matter how I would route it.

Valve rectification is harder to build, it is noisier and you need a bigger transfo. For a start use solid state if you are not comfortable with grounding and tube rolling, some tube rectifiers can make more noise.

Make sure you decouple the vibration noise from the main transformer, it will reach parts of the amplifiers and create noise, even if you cannot feel the vibration it will reach tubes and parts.
__________________
amplificateurslegrand.ca
  Reply With Quote
Old 6th December 2017, 03:11 PM   #52
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Power transformer (advise needed)
Thread cleaned up, many OT and ad hominem posts removed. Hopefully the thread can return to the worthwhile discussion that was its purpose.
__________________
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
  Reply With Quote
Old 6th December 2017, 03:12 PM   #53
Johan Potgieter is offline Johan Potgieter  South Africa
diyAudio Member
 
Join Date: May 2005
Location: Pretoria, South Africa
Back to topic.

I get the impression that transformer mechanical noise (laminatios vibrating or what?) forms some aspect of commercial models. Is that true?

To me any commercial transformer with audible (mechanical) noise is unacceptable. How difficult can it be to obviate that?
  Reply With Quote
Old 6th December 2017, 03:21 PM   #54
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
GoatGuy's Avatar
 
Join Date: Dec 2012
Location: SF Bay Area
short answer: glue

brief answer: lamination varnish and a bake out. Requires baking the transformer to above-boiling-water temp; then moving to a vacuum chamber while hot; allowing SIT time to exhaust all volatiles from core and windings. Air mostly, but a surprising amount of hydrocarbons (insulation!) and water vapor. After an amount of time in vacua that is better measured by metrology than a timer, the transformers are plunged into a pool of very thin varnish. The vacuum is released once they're submerged; the inrush of 14.7 lb/in˛ air strongly forces the varnish into every last inner crevice.

Then they're hauled out, allowed to "drip dry" for another hour. Then off to the drying kiln. Again raised to 80°C, with a lot of blowing air flow. The varnish volatiles percolate out, are wafted away. The varnish hardens. The laminations stop buzzing. Permanently. Same for the windings.

You're welcome.
GoatGuy
__________________
John Curl's Golden Rule…: 100 kHz bandwidth, 3 μs risetime, 100 W mean output, 100 V/μs slew rate, 2 Ω dynamic load, 20 amp min current source/sink
  Reply With Quote
Old 6th December 2017, 03:38 PM   #55
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
GoatGuy's Avatar
 
Join Date: Dec 2012
Location: SF Bay Area
Quote:
Originally Posted by gabdx View Post
Calculating the proper type of power transformer is difficult even for experienced builders.

You need to purchase a transformer which is designed for your circuit and labeled to provide the voltage range you want for the type of rectification.

My advice: dual power transformers is very difficult to build and lot of noise and problems can occur. I could never complete an amplifier with 3 power transformers which integrated a dedicated pre-amp and 2 mono for power sections. The ground path always carried hum no matter how I would route it.

Valve rectification is harder to build, it is noisier and you need a bigger transfo. For a start use solid state if you are not comfortable with grounding and tube rolling, some tube rectifiers can make more noise.

Make sure you decouple the vibration noise from the main transformer, it will reach parts of the amplifiers and create noise, even if you cannot feel the vibration it will reach tubes and parts.
Thanks, but to some of your advice, I call out “balderdash”.

For instance, “a transformer which is designed for your circuit and labeled to provide the voltage range you want for the type of rectification.” This is balderdash, whole.

You need to design circuits based on knowing what solid commercial 'standard' transformers put out. Its that simple. If you have identified (as a for-instance) a handful of Hammond multiple secondary transformers as being "about right", then you need to model out what choosing various versions will do to your 3 to 5 DC supply streams. If you are smart and confident with some circuit complexity in exchange for substantial design flexibility, then regulate the secondaries. Go "all DC", including filament supplies. Shield out the hum mechanically.

Seriously: the freedom that you get is awesome. You decide you need a 290 VDC (very uncommon, but hey…) power section DC supply? Get a 275–0–275 Hammond 270-FX having 173 ma HV winding, 3000 ma at 5 V, 5000 ma at 6.3 V, and get started. Your first-filtered (cap loaded rectifiers) DC will come in at 366 volts. A bit (not too much) LC filtering delivers 350 to regulators. Regulate down the 6 HV supplies independently. 170 for the 2 preamp sections, 220 for the line sections (2), and 2 × 290 V (that strange value) for the output finals.

No need for a custom transformer at all. Especially with regulation. Over 100 dB of ripple reduction. Complete freedom from mains sags, surges, digital noise, etc. Bourne type set-screw stage voltage adjustment, independent of transformer/mains and stage-to-stage interdependence.

That's how its done in the real world. The idea of having a custom mains transformer wound is just silliness: its like specifying palladium plated titanium bodied winches for a tug boat. Pretty, and pretty much useless overkill.

Or as I like to say repeatedly, "regulation young buck, regulation". And I mean the active kind, the multistage kind. It is transformational (wow, the pun is terrible).

GoatGuy
__________________
John Curl's Golden Rule…: 100 kHz bandwidth, 3 μs risetime, 100 W mean output, 100 V/μs slew rate, 2 Ω dynamic load, 20 amp min current source/sink
  Reply With Quote
Old 6th December 2017, 04:50 PM   #56
pieter t is offline pieter t  Netherlands
diyAudio Member
 
Join Date: Apr 2009
Quote:
Originally Posted by Johan Potgieter View Post
Back to topic.

I get the impression that transformer mechanical noise (laminatios vibrating or what?) forms some aspect of commercial models. Is that true?

To me any commercial transformer with audible (mechanical) noise is unacceptable. How difficult can it be to obviate that?
IMO the keyword here is "commercial".
Virtually all commercial available "off the shelve" transformers are wound with core excitations around 1.6 T.
Completely understandable as this way cost is cut (less material; less weight).
However, with core excitations approaching core saturation, risks are lurking.
Many commercial transformers are mechanically not silent (to put it mildly...).
Apparently the quality of impregnating is insufficient; I am pretty sure that not many commercial transformer companies apply the way of vacuum impregnating the way Goatguy describes as it would make a more expensive transformer.
Besides, high T transformers get rather hot as secondary power is about what the core can deliver.
Last, but maybe not least, strayfields are strongest with high core excitations.
To overcome, or maybe better put, prevent these problems from happening, in my (and others, like Tony) experience it is good practice to choose for lower core excitation; 1T is a nice upper limit.
This lower core excitation however is not so economic: for a power supply transformer with 150VA of secondary power a core of some 300VA is needed . Winding for lower core excitation requires more primary windings, so the larger winding space of the 300VA core is needed to have enough space for primary and secondary windings (apart from single or multiple screening).
At the end of this low T power supply transformer we have the advantages of:
- a cool running transformer (think of nearby electrolytic capacitors not liking heat);
- a transformer with minimal strayfield;
- a mechanically silent transformer (vacuum impregnating still necessary but less critical as the whole thing is less vibrant to begin with).
The story above applies to EI, c-core and toroidal transformers, with some peculiarities typical for the type:
- EI laminations are "loose" after assembling so good quality impregnating is very important;
- c-cores are impregnated during manufacturing, but impregnating still applies to the coil(s);
- toroidal transformers can be a nightmare: prone to core saturation; very difficult to get silent with impregnation as windings tend to be random with much room for vibration.
I don't understand toroidal power supply transformers in (mostly) SS gear as being the norm.

Last edited by pieter t; 6th December 2017 at 05:00 PM.
  Reply With Quote
Old 6th December 2017, 08:41 PM   #57
AmadeusMozart is offline AmadeusMozart  New Zealand
diyAudio Member
 
Join Date: Oct 2009
Location: New Zealand
Quote:
Originally Posted by Johan Potgieter View Post
Back to topic.

I get the impression that transformer mechanical noise (laminatios vibrating or what?) forms some aspect of commercial models. Is that true?

To me any commercial transformer with audible (mechanical) noise is unacceptable. How difficult can it be to obviate that?
It helps to use an aluminium chassis and stainless fastening material. In case of Hammond: inspect the bells and check where the the earthing wire of the internal electrostatic shield is attached. Often the bells are not sitting flat against the laminations. I also use silicone AcoustiFeet from SilentPC to stop vibrations from reaching the amplifier and the tubes. AcoustiFeet Vibration-absorbing Low Profile Silicone Feet

AM
__________________
Retired and enjoying life - I'll only be around on rare occasions.
  Reply With Quote

Reply


Power transformer (advise needed)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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Advise needed. What is this stuartmp Solid State 14 15th April 2017 12:26 PM
Power Transformer Hafler needed schillg11 Swap Meet 7 8th August 2016 08:33 PM
Power transformer repair or rewinding needed. Mr Moscode Power Supplies 0 11th January 2015 07:14 AM
Inputs needed for Power Transformer Design! zgondouin Tubes / Valves 17 15th November 2013 11:58 AM
PCB or kit for power amplifier advise NEEDED rmihai Solid State 7 29th September 2005 01:38 AM


New To Site? Need Help?

All times are GMT. The time now is 08:58 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki