Help with EL504-based amplifier - 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 27th December 2011, 12:56 PM   #1
diyAudio Member
 
Socram8888's Avatar
 
Join Date: Jan 2008
Location: Valencia, Spain
Send a message via MSN to Socram8888
Default Help with EL504-based amplifier

Hello. This is my first tube-based amplifier I've ever built, and I'm experiencing a strange issue with it.

The amplifier works well when the EL504 is heating up, but it stops working when fully heated. It works also when cooling down.

I'm following an schematic made for the PL504 but modified (I've just added another transformer for the 6.3VAC the EL504 uses)

Here's the schematic:
Click the image to open in full size.

The output of the rectified voltage measures about 31VDC (vs the original 27V the original amplifier used)

Thanks
  Reply With Quote
Old 27th December 2011, 01:35 PM   #2
diyAudio Member
 
Join Date: Oct 2011
Location: Tauberbischofsheim, Germany
Hi,

three issues to consider:

1. 31 volts B+ supply ist way too less for your tube.
2. EL or PL504 don't work too well as a single-ended class a output device.
3. A mains transformer isn't a good output transformer.

Best regards!
  Reply With Quote
Old 27th December 2011, 01:51 PM   #3
diyAudio Member
 
Socram8888's Avatar
 
Join Date: Jan 2008
Location: Valencia, Spain
Send a message via MSN to Socram8888
I don't want (or need) an HiFi quality, I'm just interested in building a very simple amp with tubes, then try building some more complex

The schematic is from the famous electronics magazine Elector:
http://www.gtlab.net/gtlab2/filemana...ow_anode_1.pdf
http://www.gtlab.net/gtlab2/filemana...ow_anode_2.pdf

Also there are videos on YT with PL504 working at an even lower voltage, this one for example: Amplificator cu tubul PL504 la 27V - YouTube

Thanks for your answer
  Reply With Quote
Old 27th December 2011, 02:31 PM   #4
Zibi is offline Zibi  Poland
diyAudio Member
 
Join Date: Jan 2006
Location: Bialystok
No bias at all.
Biasing Power Tubes
  Reply With Quote
Old 27th December 2011, 03:03 PM   #5
diyAudio Member
 
Socram8888's Avatar
 
Join Date: Jan 2008
Location: Valencia, Spain
Send a message via MSN to Socram8888
I have no 1 Ohm resistors. The lowest resistor I have are 75 Ohm resistors. Can I use these to obtain for example 7.5Ohm, then bias with that value?

So the correct schematic is this one, right?
Click the image to open in full size.
Which resistor adjusts the bias?

Sorry if these questions seems too basic or stupid, but it's my first project using tubes. Thanks for your patience
  Reply With Quote
Old 27th December 2011, 03:15 PM   #6
diyAudio Member
 
Join Date: Sep 2009
put in a 30 ohm resistor at the cathode. that should work
  Reply With Quote
Old 27th December 2011, 03:16 PM   #7
diyAudio Member
 
Join Date: Sep 2009
since u have 75 ohm resistors, put a pair in parallel at the cathode...
  Reply With Quote
Old 27th December 2011, 04:15 PM   #8
diyAudio Member
 
Socram8888's Avatar
 
Join Date: Jan 2008
Location: Valencia, Spain
Send a message via MSN to Socram8888
Thanks! That worked. I've put a 1kOhm resistor on the G1 and removed the capacitor. Now it sounds more clear than before.

A bit offtopic: would be possible to use this exact circuit with this other tube? http://tubedata.tubes.se/sheets/127/1/17DQ6B.pdf . They're both dirty cheap, but these use a more common octal socket
  Reply With Quote
Old 27th December 2011, 04:45 PM   #9
diyAudio Member
 
Join Date: Jan 2008
Location: Virginia
The difference between "working" and "working well" is made by the right supply voltage.
Sure, it "works" with 30V but that is still in the unlinear region of the tube (knee), so you will have lots of distortions, especially at low level passages.
Phillips recomens supply voltages between 170-230V for 504 tubes.

The second tube is a horisontal deflection tube. Very high voltage, low current, works best in pulses... not an audio device.

Last edited by SoNic_real_one; 27th December 2011 at 04:55 PM.
  Reply With Quote
Old 27th December 2011, 05:09 PM   #10
diyAudio Member
 
aardvarkash10's Avatar
 
Join Date: Mar 2007
Location: Auckland, NZ
actually, the (X)dq6b has been used successfully as an output tube, but only in PP circuits (or OTL). It seriously sucks as an SE tube...
__________________
"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

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
Impedans of trafo for EL504 inSE Ryssen Tubes / Valves 10 17th August 2012 09:39 AM
EL504/PL504 spice model aparatusonitus Tubes / Valves 7 29th January 2009 09:15 PM
LM3886 based amplifier russo Chip Amps 18 4th February 2008 11:27 AM
FS: 22 pcs NOS NIB RSD EL504. webercarbmann Swap Meet 0 25th July 2003 02:03 PM
Trade EL504 - ? webercarbmann Swap Meet 0 23rd June 2003 11:07 PM


New To Site? Need Help?

All times are GMT. The time now is 04:40 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