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

Why no tiny output transformers?
Why no tiny output transformers?
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 14th June 2018, 02:03 AM   #51
Hearinspace is offline Hearinspace  Canada
diyAudio Member
 
Join Date: Jun 2008
Why no tiny output transformers?
Quote:
Originally Posted by BJosephs View Post
a high enough inductance to maintain low frequency extension is in conflict with reduced size.
Did you see Bill Whitlock's reference to "legendary wisdom" suggesting as a rough guide a core size of 0.34 pounds and 1.4 cubic inches per Watt for a "good fidelity output transformer" ?

Not that big for something under 5 Watts.
  Reply With Quote
Old 14th June 2018, 02:07 AM   #52
nigelwright7557 is offline nigelwright7557  United Kingdom
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by Lingwendil View Post
My last two builds use Toroids from Antek, a 10 volt secondary works great for ~4.2k:8 if you run the primaries in series, and 5 volts works for ~17k:8 for my 6SN7 builds.
The transformer on the right is the 12 volt mains totoridal output transformer.

Click the image to open in full size.
__________________
PCBCAD51 pcb design software. 2018 version out now with lower prices >> http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 14th June 2018, 07:55 PM   #53
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by Hearinspace View Post
Did you see Bill Whitlock's reference to "legendary wisdom" suggesting as a rough guide a core size of 0.34 pounds and 1.4 cubic inches per Watt for a "good fidelity output transformer" ?

Not that big for something under 5 Watts.
Mhhh..it's not clear if that rule is for PP amps or SE. He mentions that rule where he talks about PP amps and then the SE amp "section" is detached...
Should look into the reference (Langford book).

Anyway for PP it's overkill. For SE is ok.
According to that formula the core weight should be over 15Kg for 100W....it sounds ok to me only if SE.

For PP, if you specify the full power @28-30Hz for a power bandwidth (-3 dB) starting from 20-22 Hz you will save quite some weight. In my opinion is it's a more rational solution. This has nothing to do with frequency response that will typically be -3 db around 1-2Hz!
For example, 100W @30Hz with max AC induction of 0.85T and 1A/mm^2 for AC current density and approx. 0.2 dB loss will require an EI core of 5Kg. It could be the EI-135 (European metric) with 45x60 mm core area which is already a bit oversized. 4.5x55 would weight 5Kg....This would be an excellent transformer from any point of view. No compromise if properly wound. Granted!

If I want to exaggerate and get the same performance above at 20Hz then I would need a core of about 6.5Kg.


For SE, and same performance, I would need 4x weight because of DC current flowing.

Less weight for C cores.

Last edited by 45; 14th June 2018 at 08:08 PM.
  Reply With Quote
Old 14th June 2018, 08:58 PM   #54
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by BJosephs View Post
I reached out to the author of that page and he was using a 70v transformer with 1/4W tap.

In all honesty, I didn't start this thread to try and find a work around.
I have not gone through the thread to find out. What do you want to build? Which power tube for your 1W SE amp? Triode? Pentode?
  Reply With Quote
Old 15th June 2018, 03:27 AM   #55
BJosephs is offline BJosephs  United States
diyAudio Member
 
Join Date: May 2011
Location: Bridgewater Ma, USA
In all honesty it was just curiosity. However, the day the thought occurred to me I was thinking about a push pull amp using a dual triode (I’m partial to ECC99) for a little desktop amp. That Hammond 109 with a 10k:3.2 would probably work.
  Reply With Quote
Old 15th June 2018, 04:05 AM   #56
Lingwendil is offline Lingwendil  United States
Now with high-fructose ASSAULT-gluten!
diyAudio Member
 
Lingwendil's Avatar
 
Join Date: Apr 2008
Location: Oakley California
Why no tiny output transformers?
Check out my flea amplifier thread for something similar, I use the 6SN7 as outputs, and use small Toroids for 1.3w per channel or so. No reason you couldn't make it work with something like the ECC99 with some details being changed to suit.

6SN7 push pull flea amplifier project

I've worked up some PCBs that will go out to some members for testing soon.
__________________
Check out My 6SN7 Push-pull Flea Amplifier project! PCB COMING SOON!
  Reply With Quote
Old 15th June 2018, 02:30 PM   #57
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by BJosephs View Post
In all honesty it was just curiosity. However, the day the thought occurred to me I was thinking about a push pull amp using a dual triode (Iím partial to ECC99) for a little desktop amp. That Hammond 109 with a 10k:3.2 would probably work.
I think it's a better idea. I have myself as back-up amp PCL86 SE amp on my bench to listen to the radio. It's nice but and if one wants excellent performance the transformer is not can't be cheap. Not because of the materials but for the work needed. Yes, there are cheap SE transformers around but honestly one only gets what he is paying for in return.
For PP it's much better scenario in this respect.
  Reply With Quote
Old 15th June 2018, 06:09 PM   #58
kmtang is offline kmtang  Canada
diyAudio Member
 
kmtang's Avatar
 
Join Date: Nov 2004
Location: Vancouver
Recently, I bought two Lundahl LL2766 SE OPT for building of the stereo 45 tube power amp. The size of the transformer is quite small in comparison with the LL1620 OPT that I used to use. Even though the low frequency can't match with the LL1620, the bass performance of the LL2766 is reasonably good and exceed my expectation.
  Reply With Quote
Old 15th June 2018, 08:34 PM   #59
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Without going too much into details, C cores are more efficient because grains are 100% oriented. They can work up to 1.6 T induction if good grade (possibly 1.7T in best grades) without relevant distortion at low frequency, at least down to 30Hz in SE applications and lower in PP. In EI cores only about 2/3 of the grains are oriented and saturation doesn't surge uniformly. Saturation hots spots do have a visible influence on distortion and inductance. To get a performance close to that of C cores one has to stop at about 1T or accept some more distortion below 35-40 Hz for running up to 1.2T. So for the same core area and turns one can apply 30-60% more volts resulting in more headroom or can reduce the size of the core for the same headroom. Toroidals too are like C cores.
  Reply With Quote
Old 17th June 2018, 02:00 PM   #60
kmtang is offline kmtang  Canada
diyAudio Member
 
kmtang's Avatar
 
Join Date: Nov 2004
Location: Vancouver
Default a picture of my Helena 45 stereo SE amp with LL2766 OPT

34560304_10155862941958143_5881090076938600448_o.jpg

The driver is paralleled 7F7 tube and RC coupled to the self biased 45 power tube.

Double PI L-C filter.

Johnny

Last edited by kmtang; 17th June 2018 at 02:02 PM.
  Reply With Quote

Reply


Why no tiny output transformers?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
Orange Tiny Terror Output Transformer? PB2 Instruments and Amps 17 30th April 2015 07:36 AM
Looking for a decent pair of 807(output tube) output transformers hatrack71 Swap Meet 4 5th April 2012 07:43 PM
Difference between SE output transformer and push-pull output transformers hilbert_mostert Tubes / Valves 12 8th March 2009 05:10 PM
Help identifying a pair of output transformers and power transformers mjk130 Parts 3 30th January 2009 10:44 AM
any good tiny tiny tweeters? THOR Multi-Way 18 28th June 2004 06:42 AM


New To Site? Need Help?

All times are GMT. The time now is 01:36 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki