EL84/6SN7 tube amp - 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 28th December 2010, 08:03 PM   #1
riktw is offline riktw  Netherlands
diyAudio Member
 
Join Date: Sep 2007
Default EL84/6SN7 tube amp

Hello

i got some tubes laying around and i want to make an amplifier with them
with some help from the internet, especially this sites i tried to design one.

How to design valve guitar amplifiers
How to Design an SE Power Amplifier

i want to make an EL84 amplifier, EL84 as triode and an 6SN7 as input stage.
i already got the transformers (got them on a dutch ebay site, 30 euro's for 2 OPT and a power supply transformer) and i got the tubes.
The OPT's have a 1:30 winding ratio, i got 4 ohm speakers so that means 30*30*4 = 3600ohm

for the questions:
the EL84 stage requires a 20V swing to get max power, the 6SN7 stage amplifies 15 times.
so i would need 1.33V input fox max output.
as far as i know a CD player delivers roughly 2Vpp but do i need 1.33Vpp fox max output of 1.33Vrms?
i expect at least 50 different mistakes but did i make some and so yes what and where?

here is my design with the formula's i used in them:

Thanks, rik
Attached Images
File Type: png EL84 stage2.png (142.7 KB, 325 views)
File Type: png tubeamp.png (34.4 KB, 323 views)
File Type: png 6SN7 stage.png (170.7 KB, 319 views)
  Reply With Quote
Old 28th December 2010, 08:30 PM   #2
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
At first, you seem to get some 2 watts out from the amplifier with no so small distortion. Is this satisfying you ?

You need 1,33 Vpp to input of 6SN7. This is 0,47 Vrms.

Your design procedure seems fully right.
  Reply With Quote
Old 28th December 2010, 08:33 PM   #3
diyAudio Member
 
aardvarkash10's Avatar
 
Join Date: Mar 2007
Location: Auckland, NZ
have a read of this for a good easy explanation of the concepts.

Your output transformers are not ideal for 4 ohm speakers using EL84 tubes - the EL84 prefers closer to 8k impedance. They will be fine if you use 8 ohm speakers.
__________________
"Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report
  Reply With Quote
Old 28th December 2010, 08:39 PM   #4
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
Quote:
the EL84 prefers closer to 8k impedance.
Philips recommends 3,5 kohms load impedance for triode connected EL84 ( with 250 V anode voltage and 36 mA anode current).
  Reply With Quote
Old 28th December 2010, 08:47 PM   #5
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
You need an input capacitor.

I would also recommend an RC between EL84 supply and the 6SN7.
This will reduce hum and feedback.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 28th December 2010, 09:08 PM   #6
riktw is offline riktw  Netherlands
diyAudio Member
 
Join Date: Sep 2007
i will put an RC network in the power supply, 100uF 47ohm 100uF should work good enough
input capacitor is a good point indeed, shall add it.

and yes, 2 watts is enough, if this works properly i can start thinking about making a bigger tube amp with good new transformers.
the GM70 tube is one i really like lookwise, who knows if this works out perfectly i can build a nice GM70 amp
this is pure practice
  Reply With Quote
Old 28th December 2010, 09:33 PM   #7
diyAudio Member
 
aardvarkash10's Avatar
 
Join Date: Mar 2007
Location: Auckland, NZ
Quote:
Originally Posted by artosalo View Post
Philips recommends 3,5 kohms load impedance for triode connected EL84 ( with 250 V anode voltage and 36 mA anode current).

Mea culpa - I was thinking pp.
__________________
"Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report
  Reply With Quote
Old 28th December 2010, 11:03 PM   #8
diyAudio Member
 
Miniwatt's Avatar
 
Join Date: Nov 2004
Location: Den Haag
Quote:
Originally Posted by nigelwright7557 View Post
You need an input capacitor.
And why is that?
  Reply With Quote
Old 28th December 2010, 11:07 PM   #9
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by Miniwatt View Post
And why is that?
Because you dont know what he is going to connect it to.
It might have DC on it and upset the valves working conditions.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 28th December 2010, 11:47 PM   #10
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I don't use input capacitors, as they say the best cap is no cap, however and this is a big however; I always make sure that my sources (a line stage in most cases) have no more than a couple of mV of DC on their outputs.

All of my digital sources are balanced and transformer coupled so no DC there. The line stage is also transformer coupled so again no DC there.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  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
Suppo Audio EL84 PP Tube Amp boudy Swap Meet 2 15th February 2010 01:42 PM
set el84 tube amp sarrisk Tubes / Valves 15 9th September 2008 01:42 AM
Retubing my amp (EL84, ECC81, ECC83) - Tube recommendations? horace Tubes / Valves 18 18th December 2007 01:54 PM
fs/swop, el84 hybrid tube amp psychosteve Swap Meet 0 11th October 2004 02:10 PM
Replacing a driver tube in an existing EL84 SE Amp corbato Tubes / Valves 29 16th February 2003 05:33 PM


New To Site? Need Help?

All times are GMT. The time now is 04:37 AM.


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