Single-ended-series amp with a "1 winding" transformer - 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 4th September 2007, 11:17 AM   #1
tubee is offline tubee  Netherlands
diyAudio Member
 
tubee's Avatar
 
Join Date: Jul 2004
Location: Netherlands
Default Single-ended-series amp with a "1 winding" transformer

Hello

I was busy in my garage and found a sketch again of a 20 Watt tube poweramp. I redraw it and made a photo of it to show here, comments welcome.

The idea is to make a simple power amp with the tubes, chokes and transformers i have here at hand. Have a lot of EF86's penthodes, four EL36 power penthode with anode cap on top.(are slightly smaller then the well known EL34)

Input stage is simple of in triode operating penthodes, second EF86 is for phase reversal.
The virtues of the single ended endtube design is the simplicity, and the rather low impedance, one kathode drives the output transformer and one anode. This low impedance gives a chance of using a simple transformer of about 500 ohms The transformers i have here are with a single winding, this is better for high frequency coupling to the speaker. But on the contrary it needs an output cap to the transformer, otherwise the core is saturated due to dc current.
Each EL36 is in triode and top and bottom tube has to be biased with its own negative supply, automatic bias with a resistor is not easy (nor possible?) with series endtubes.

Well, comments welcome!
Click the image to open in full size.
__________________
Daisy Bell
  Reply With Quote
Old 4th September 2007, 03:00 PM   #2
diyAudio Member
 
Tubes4e4's Avatar
 
Join Date: Jul 2005
Location: Leverkusen
Hello Tubee,

interesting circuit, but for better performance, the upper tube should get about 3...4 times the driving swing the lower tubes gets. (Unloaded mu of trioded EL36 is about 5 times.)

The easiest method to get such a drive ratio would be to follow up the concertina with a differential stage, or replace it by a LTP splitter, with one of the both plate resistors split into two serialized ones giving the desired ratio from the tap between them.

If of interest to you, you can find the triode strapped plate curves for EL36
here at my site.

Regards, Tom
__________________
If in doubt, just measure.
  Reply With Quote
Old 4th September 2007, 04:33 PM   #3
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
...also, it may be difficult to get 20W out of two EL36 in triode... it will have to run class AB.
  Reply With Quote
Old 4th September 2007, 07:31 PM   #4
tubee is offline tubee  Netherlands
diyAudio Member
 
tubee's Avatar
 
Join Date: Jul 2004
Location: Netherlands
Thanks for replys Tubes4e4 and ilimzn

Interesting thought yes the different driving of the endtubes, didn't thought of that! I have somewhere a good phase inverter schematic which is able to drive unequal, i think it's a paraphase, not sure how it's called. Have to get into tubes again a little, did a lot of other stuff lately.

The stated 20 watt is a little overated yes, realised it when i closed the post. A single EL34 in class A in triode delivers about 8 Watt, so this circuit max 16 watt.

The coupling cap on the end can be a computer grade lytic, or a black gate (expensive!) First find some stuff out of a box and see if the schematic works. The end transformers did i find in big trashbin at street, two identicals.
__________________
Daisy Bell
  Reply With Quote
Old 4th September 2007, 09:08 PM   #5
poynton is offline poynton  United Kingdom
diyAudio Member
 
poynton's Avatar
 
Join Date: Mar 2005
Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
It looks like an OTL design with a matching transformer

Andy
  Reply With Quote
Old 5th September 2007, 04:56 AM   #6
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
It looks like the Philips SRPP amplifier used to drive their 800 ohm speakers.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 5th September 2007, 05:31 AM   #7
diyAudio Member
 
Tubes4e4's Avatar
 
Join Date: Jul 2005
Location: Leverkusen
Hi Dave,

Quote:
Originally posted by planet10
It looks like the Philips SRPP amplifier used to drive their 800 ohm speakers.
Nah, that Philips one is quite different; SRPP indeed, single drive (lower tube only), pentode mode, no OPT.

Tom
__________________
If in doubt, just measure.
  Reply With Quote
Old 5th September 2007, 05:41 AM   #8
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
The ones i've had thru here all had output chokes (like this one)

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 5th September 2007, 06:38 AM   #9
poynton is offline poynton  United Kingdom
diyAudio Member
 
poynton's Avatar
 
Join Date: Mar 2005
Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
Quote:
Originally posted by poynton
It looks like an OTL design with a matching transformer

Andy
What I meant was that, regardless of the matching transformer, the usual criticisms of OTLs can be made eg cathode follower/anode follower etc.. (post 2)

Andy
  Reply With Quote
Old 5th September 2007, 07:28 AM   #10
diyAudio Member
 
Join Date: Jan 2003
Location: Sweden
Quote:
the usual criticisms of OTLs can be made eg cathode follower/anode follower etc.. (post 2)
Yes and of course the same methods as used in OTL to achieve balance can be used, e.g Futterman or other methods. BTW the method suggetsed in post 2, (changing the gain of the signal to the lower tube dosen't work as the gain of the lower tube changes with different load, therefore static gain balancing only work for one load impedance value, the Futterman method achieve full balance regardless of output impedance.

Regards Hans
  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
"Mighty Mite" Single Ended Amplifier wrenchone Tubes / Valves 13 20th October 2008 04:57 AM
glass audio 1995 "Single Ended Glory" habsrock93 Tubes / Valves 3 22nd June 2008 02:10 AM
Building a high quality gainclone toroid coupling transformer with "tubeness" winding ionomolo Chip Amps 16 13th February 2008 01:20 PM
FS: Homebuilt "Aikido" 2A3 single ended triode amp jim_vt Swap Meet 11 21st January 2006 03:38 PM
Using Telefunken "Tank" transfomers for a single ended el84 amp? ark Tubes / Valves 13 8th March 2004 11:32 PM


New To Site? Need Help?

All times are GMT. The time now is 10:36 PM.


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