EL84 custom monoblocks - 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 17th July 2015, 06:53 PM   #1
Audio enthusiast
diyAudio Member
 
Join Date: May 2015
Location: Boone, north carolina
Default EL84 custom monoblocks

I acquired 2 el84 custom monoblocks at decent price. Has two 5687's in front of two el84's. Lacks clarity, curious as to anyone's thoughts on how the internals are wires
Attached Images
File Type: jpg image.jpg (793.6 KB, 626 views)
__________________
i know just enough to get me in trouble
  Reply With Quote
Old 17th July 2015, 06:54 PM   #2
Audio enthusiast
diyAudio Member
 
Join Date: May 2015
Location: Boone, north carolina
Wrong photo first time. Looks to me like heater wiring could be lot better. Wires to output transformer are twisted, not sure if has positive effect on cancelation or just personal preference
Attached Images
File Type: jpg image.jpg (461.1 KB, 587 views)
__________________
i know just enough to get me in trouble

Last edited by Flipmoore; 17th July 2015 at 06:57 PM.
  Reply With Quote
Old 17th July 2015, 11:35 PM   #3
diyAudio Member
 
Join Date: May 2006
First thing I notice is it does not have the safety ground connected, so it could kill you. Otherwise, you should create a schematic as a first step.
  Reply With Quote
Old 18th July 2015, 12:22 AM   #4
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Besides the safety earth ground being absent, the power supply ground and signal grounds are at opposite ends of the chassis. Ground buses are good but should come together at a common star point usually near the center of the chassis. The center is not mandatory but always works right for me. And this would affect mostly hum levels if that's what you mean by clarity.

The filament supply appears to be DC and grounded on one side. This should not be a problem in general for a simple design like this one. And twisting the plate and screen output transformer leads shouldn't cause trouble either. Poor clarity can come from many causes and a diagram of the circuit might reveal a circuit design flaw such as operating points for the stages. Parts quality looks acceptable from what I can see.
__________________
"I regard the brain as a computer which will stop working when it's components fail. There is no heaven or afterlife for broken down computers. That is a fairy story for people afraid of the dark." ~Stephen Hawking
  Reply With Quote
Old 18th July 2015, 02:59 AM   #5
Audio enthusiast
diyAudio Member
 
Join Date: May 2015
Location: Boone, north carolina
The earth ground has been fixed on both amps, I got them at a decent price because they had a him that the owner couldn't pinpoint and fix. That took care of any hum that I can hear. I asked the last owner for schematic and haven't heard back from them. I will see what I can draw up
__________________
i know just enough to get me in trouble
  Reply With Quote
Old 18th July 2015, 03:00 AM   #6
gabdx is offline gabdx  Canada
diyAudio Member
 
Join Date: Jan 2008
There is no feedback so the output impedence will be very high for an EL84 in pp.

The heater seems fine , especially if it doesn't hum.

Grounding this chassis should be a priority!
__________________
amplificateurslegrand.ca
http://www.amplificateurslegrand.ca/
  Reply With Quote
Old 18th July 2015, 09:41 AM   #7
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Looks like an attempt at a bus ground by someone who doesn't understand bus grounds. That may explain hum.

Twisting OPT wires is helpful. Twisting DC heater wires is a waste of time, but won't do any harm.
  Reply With Quote
Old 18th July 2015, 05:26 PM   #8
diyAudio Member
 
directdriver's Avatar
 
Join Date: Nov 2005
The output transformers appear to be Stancor 51-29 from Heathkit 6BQ5 amps like EA2, EA3, SA2, AA161, AA13, AA151, AA40, etc... They are great irons and I think you have a good foundation to build on. The transformers are ultralinear UL type and I think there is global feedback, judging by the picture. Notice yellow wire off of 8 ohm tap back to the input tube.
  Reply With Quote
Old 19th July 2015, 02:22 AM   #9
Audio enthusiast
diyAudio Member
 
Join Date: May 2015
Location: Boone, north carolina
I am not very proficient at lt spice or drawing schematics at all. But I will do my best to make an interpretable version
__________________
i know just enough to get me in trouble
  Reply With Quote
Old 19th July 2015, 06:27 AM   #10
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
whatever you do, never use the chassis metalwork to run your psu return currents....
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
  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
EL84 driving EL84 SET with fixed bias cotdt Tubes / Valves 13 16th March 2014 02:18 PM
Custom tubes4hifi m-125 monoblocks Alfi1966 Tubes / Valves 9 10th February 2014 04:13 PM
FS: EL84 EI Yugoslavia & EL84 Tungsram NOS Bulk radiostar Swap Meet 3 29th January 2012 08:46 AM
Trade Custom Speaker Horns for Custom Amp brsanko Tubes / Valves 3 6th July 2010 05:32 AM


New To Site? Need Help?

All times are GMT. The time now is 08:15 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2