Go Back   Home > Forums > >

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

EL84 tube amp build, how to start?
EL84 tube amp build, how to start?
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
Old 30th November 2020, 06:33 PM   #131
wg_ski is offline wg_ski  United States
diyAudio Member
 
Join Date: Oct 2007
Quote:
Originally Posted by Kay Pirinha View Post
This might end in death cathodes in tubes that are run withoud cathode current for a long time.
Only heat one cathode. It means youre stuck with 6 volts, rather than the option of running off 12.
  Reply With Quote
Old 30th November 2020, 06:38 PM   #132
Kay Pirinha is offline Kay Pirinha  Germany
diyAudio Member
 
Kay Pirinha's Avatar
 
Join Date: Oct 2011
Location: Somewhere in Germanistan
Oh, good idea! You can also feed them off 12.6 V if you connect the cathodes of two halved tubes in series.
Best egards!
__________________
"I spent a lot of money on booze, birds and fast cars. The rest I just squandered." (George Best)
  Reply With Quote
Old 30th November 2020, 06:41 PM   #133
wg_ski is offline wg_ski  United States
diyAudio Member
 
Join Date: Oct 2007
If both are either AX7 or AU7. Can’t mix if the heater currents aren’t the same.
  Reply With Quote
Old 30th November 2020, 06:42 PM   #134
Kay Pirinha is offline Kay Pirinha  Germany
diyAudio Member
 
Kay Pirinha's Avatar
 
Join Date: Oct 2011
Location: Somewhere in Germanistan
Of course. Or 12AT7 and possibly more.
Best regards!
__________________
"I spent a lot of money on booze, birds and fast cars. The rest I just squandered." (George Best)
  Reply With Quote
Old 30th November 2020, 07:31 PM   #135
Francois G is offline Francois G  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Illinois
Quote:
Originally Posted by Jones880 View Post
Ok, thanks. I'm gonna start ordering parts I guess.

Just out of curiosity:

It's said a few times that a 12AU7 would be better for the concertina. This is I presume Because of the larger Ia? This would probably also mean that the grid leak resistors of the EL84 are less of a load to the concertina.

I was trying to use the 2 triodes of the same tube in the same channel. But I could use the 2 half's of an 12AX7 as input stages for 2 channels and the same with the 12AU7 as concertina for the 2 channels. However would this not also mean there's a high risk of x-coupling between channels?....
Jones880,

If you want to explore this direction I recommend a review of the diytube design by Parks Audio that uses one 12ax7 section for voltage amplification and both 12au7 sections for phase splitting. I built it and it is a very fine EL84 amplifier. Your concern about cross-coupling between channels in one double triode is valid, but in practice in this application that proved to be a non-issue.

Unfortunately the PCBs are no longer available, but it would not be difficult to hardwire build it.

See: http://www.diytube.com/st35/ST35REVE.pdf
  Reply With Quote
Old 30th November 2020, 08:12 PM   #136
Ketje is offline Ketje  Belgium
diyAudio Member
 
Ketje's Avatar
 
Join Date: Dec 2012
Location: Flanders
The EL84 is a very easy to drive tube.No problem for the ECC83.
Philips EL84 datasheet gives max Rg1 (the load for the concertina) 1M with auto(cathode) bias ande 300k with fix bias.
Most amps use 470k with cathode bias but there are stories about runaway tubes.
So, to be on the save side, I proposed 330k no need to go lower.
330k//100k= 77k the real AC-load.10Vtop (max drive) is a current change of 130A on 740A bias, no problem.
Mona
  Reply With Quote
Old 1st December 2020, 10:59 PM   #137
Jones880 is offline Jones880  Belgium
diyAudio Member
 
Join Date: Mar 2017
Location: Antwerp
Parts are ordered!

exciting!

Will start building around X-mas (if parts arrive in time)
Let's hope all goes well

Many thanks again to all who helped me. I'll probably be back to share some pictures while building. This is an awesome community
  Reply With Quote
Old 1st December 2020, 11:17 PM   #138
Schmitz77 is offline Schmitz77
diyAudio Member
 
Join Date: Apr 2015
Exciting!
Attached Images
File Type: jpg index.jpg (6.3 KB, 48 views)
  Reply to this post

Reply


EL84 tube amp build, how to start?Hide this!Advertise here!
Thread Tools

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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Power soft start board / amp delay soft start board what is it ??? thesaintxxx Power Supplies 5 18th September 2016 07:38 AM
EL84 driving EL84 SET with fixed bias cotdt Tubes / Valves 13 16th March 2014 03:18 PM
5W EL84 drive EL84 SE Audio_idiot Tubes / Valves 31 31st May 2012 09:38 PM
FS: EL84 EI Yugoslavia & EL84 Tungsram NOS Bulk radiostar Swap Meet 3 29th January 2012 09:46 AM
EL84 driving EL84 SEP tweakk Tubes / Valves 22 9th March 2011 12:23 PM


New To Site? Need Help?

All times are GMT. The time now is 03:27 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki