Fender 125A20B output transformers? - 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 13th September 2009, 11:59 PM   #1
atnaat is offline atnaat  Wales
diyAudio Member
 
Join Date: Jun 2005
Location: Cardiff
Default Fender 125A20B output transformers?

Building my first project a Mullard 3-3. I'm building it to see If I like the valve sound. It has a primary impedance of 22,800 where are the Mullard states I should use an output transformer with a primary impedance of 5000 ohms.

What would I see with the increase of impedance, an severely decreased frequency response? If so do you think there would still be enough of the spectrum test the water with the valve sound?
  Reply With Quote
Old 14th September 2009, 03:01 AM   #2
rman is offline rman  Canada
diyAudio Member
 
rman's Avatar
 
Join Date: Oct 2007
Hi.

What are you building? Is it a guitar amp? It seems that transformer is meant to drive a guitar reverb tank circuit. Too high a primary impedance will step down the output of the tube too much and give you a very low power output.

Cheers.
Rolf.
  Reply With Quote
Old 14th September 2009, 03:19 AM   #3
rman is offline rman  Canada
diyAudio Member
 
rman's Avatar
 
Join Date: Oct 2007
Okay I see what this is.

http://www.r-type.org/static/3-3.htm

Try Edcor Transformers. They make excellent and inexpensive small output transformers. Are you going to make a stereo version? With or without the tone controls?

Good luck with your project. I don't know how good an amp this is but the sound will probably surprise you if get it working right and use good parts. The Edcor XSE15-8-5k Transformer would be an excellent choice assuming you are running 8 ohm speaker(s).

Cheers.
Rolf.
  Reply With Quote
Old 14th September 2009, 08:13 PM   #4
atnaat is offline atnaat  Wales
diyAudio Member
 
Join Date: Jun 2005
Location: Cardiff
Thanks for the reply rolf. Those transformers are so cheap! It's going to be one mono-block with a volume control. I'm going to use it as a platform to see If I want to build a stereo pair of valve amps and pre-amp (may or may not be based on Mullard 3-3).

What's the best site to deal with in the UK for valve stuff? Also what's the general consensus on the Hammond transformers?
  Reply With Quote
Old 15th September 2009, 01:32 AM   #5
rman is offline rman  Canada
diyAudio Member
 
rman's Avatar
 
Join Date: Oct 2007
I
Quote:
'm going to use it as a platform to see If I want to build a stereo pair of valve amps and pre-amp (may or may not be based on Mullard 3-3).
Have fun building this amp and learn from it but I wouldn't judge tube gear in general based on what you hear from it. this amp uses a fair bit of negative feedback to linearize inherent distortions. Most modern DIY tube stuff is made to be low in unpleasant harmonic distortion. with little or no added feedback.

Maybe someone else reading this knows this amp and how it sounds? Alternatively If you are not too far along with this project you could get suggestions for other simple but very nice sounding amplifiers. my personal suggestion would be this. http://the-planet.org/6EM7.html

Sorry I can't answer your other questions

Cheers.
Rolf.
  Reply With Quote
Old 15th September 2009, 11:10 PM   #6
atnaat is offline atnaat  Wales
diyAudio Member
 
Join Date: Jun 2005
Location: Cardiff
I've thought about it, I think I might as well build something high quality. What do you think about the Mullard 5-10? Or the 5-20? I'm quoting Mullard designs because I have the book in-front of me and the details of construction are quite complete, which I think will help overcome the learning curve. I can even make the chassis in a metal working shop I have access too. However I like the look of that SET project!

http://www.r-type.org/static/5-10.htm
http://www.r-type.org/static/5-20.htm

http://www.r-type.org/static/pre.htm (preamplifier for 5-20)
  Reply With Quote
Old 15th September 2009, 11:35 PM   #7
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by atnaat View Post
Building my first project a Mullard 3-3. I'm building it to see If I like the valve sound. It has a primary impedance of 22,800 where are the Mullard states I should use an output transformer with a primary impedance of 5000 ohms.

What would I see with the increase of impedance, an severely decreased frequency response? If so do you think there would still be enough of the spectrum test the water with the valve sound?
I'm pretty sure the Fender transformer you have is designed for a single ended amp and the Mullard design is push-pull. Likely you would be able to hear sounds but it would be a poor test of wetter you like the "tube sound" as it would be badly distorted.

Also, if you look at the Fender design they purposely filter out the lows before they send the signal to the transformer, that transformer is not designed for anything below about 200Hz. So no bass. After all the goal was to drive a spring reverb tank not a hifi speaker

For a three watt push pull look for a transformer rated at about 15W.

save that transformer. It would make a good headphone amp. Drive it with a 12AU7 tube and at 1/2 watt or less it would have decent bass but at three watts no.
  Reply With Quote
Old 15th September 2009, 11:50 PM   #8
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by atnaat View Post
I've thought about it, I think I might as well build something high quality....
Good idea. But build a high qualiity SIMPLE design. The mullard push-pull has lots of parts and many ways to go wrong.

Try building a single end (SE) design. These amps arguably sound better than push pull and have about 1/2 the number of parts. The cost is that SE amps have less power. You can build a low power SE stereo amp with three tubes. Start with something the uses one 6V6 or EL84 per channel.

Basic rule: Do NOT build anything you can not diagnose and debug. I'd actually recommend a low power, low gain guitar amp as your first project but that's useless if you don't play guitar, so the next simplest thing is a small SE stereo amp.
  Reply With Quote
Old 16th September 2009, 01:38 AM   #9
rman is offline rman  Canada
diyAudio Member
 
rman's Avatar
 
Join Date: Oct 2007
Hi.

I agree with Chris with the exception that he is wrong the 3-3 being Push Pull.
When I Googgled it and found that link I put in post three, the Schematic clearly shows it to be single ended. Maybe all their other designs are push pull?

Cheers.
Rolf.
  Reply With Quote
Old 16th September 2009, 01:55 AM   #10
rman is offline rman  Canada
diyAudio Member
 
rman's Avatar
 
Join Date: Oct 2007
I built that 6em7 dc amp as my first project. It is dead simple. Really about as simple as an amplifier can get. The sound is truly excellent as well, it will really give you the tube sound you want to hear. The only reason you might need to build a replacement for it, besides having gotten the Diy bug, would be if you really needed more power.

Use those Edcor transformers, and try to get new old stock tubes. If you have to use used tubes, get several so you can match up a pair that give at least close to the specified voltages and are not to different from each other. you can use a 5ar4 rectifier tube, they are still being made and are common.

Cheers.
Rolf.
  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
Fender "Evil Twin" Hi/Low output = same level jl_lensman Tubes / Valves 4 24th April 2009 11:49 PM
Difference between SE output transformer and push-pull output transformers hilbert_mostert Tubes / Valves 12 8th March 2009 06:10 PM
Help identifying a pair of output transformers and power transformers mjk130 Parts 3 30th January 2009 11:44 AM
Fender Output transformer as an audio amp part zxx123 Tubes / Valves 6 18th January 2005 02:12 AM
Fender Champ: What Transformers? edsmith Tubes / Valves 2 6th August 2004 01:14 PM


New To Site? Need Help?

All times are GMT. The time now is 07:45 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