6L6GC instead of EL34 - 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 12th August 2014, 02:12 PM   #1
diyAudio Member
 
Join Date: Jul 2014
Location: The Netherlands
Default 6L6GC instead of EL34

Hi,

I have a Palcom TA-70 tube amp (same as Dynavox VR70) that I have been modding. Replaced all caps with high end ones, nice NOS RCA pre amp tubes. This amp uses 4 EL34's and there is enough bias range for 6L6GC tubes. Can I just put them in with a rebias or do I need to change more to be able to safely use 6L6GC's?
I have a nice quad of RCA blackplate 6L6GC's that I would like to use :-)
  Reply With Quote
Old 12th August 2014, 02:45 PM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
It won't be optimum, but it won't blow up. The 6L6 series works better with a somewhat higher plate load impedance and requires a higher voltage drive compared to EL34.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 12th August 2014, 03:07 PM   #3
diyAudio Member
 
Join Date: Jul 2014
Location: The Netherlands
Thanks, I just put them in and they sound nice. The amp seems a bit louder at the same volume setting.
  Reply With Quote
Old 12th August 2014, 08:32 PM   #4
diyAudio Member
 
Join Date: Jul 2014
Location: The Netherlands
Looking at the scematic, what should be changed for a better match, if needed?
The sound is allready amazing
Attached Images
File Type: jpg image.jpg (78.5 KB, 346 views)
  Reply With Quote
Old 12th August 2014, 08:37 PM   #5
diyAudio Member
 
Join Date: Jul 2014
Location: The Netherlands
If there are modifications that can be made to optimize the amp for 6L6 i'd like to make them , so any help is appriciated.
  Reply With Quote
Old 12th August 2014, 09:09 PM   #6
diyAudio Member
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Send a message via Skype™ to JonSnell Electronic
I would set the bias to read;
Anode dissipation, say 25Watt, divided by the HT multiplied by 0,707 is the dissipation of the valve including the screen grid. The screen grid uses about 5% of the anode value.
So for a warm class A 27 Watt bias, set the voltage drop across the 10R cathode resistor to (27/420X0.707) 45mA = 450mV
For a cooler running Class Ab use 17/420X0.707 = 28mA = 280mV

The 6L6GCW or 5881 is on a par with the KT88. The best valve designed for high power audio.
I prefer around 35mA
__________________
www.flyingmole.co.uk For World Wide support for Flying Mole, Class D, Refurbishment and Repairs. www.jonsnell.co.uk
  Reply With Quote
Old 12th August 2014, 09:25 PM   #7
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
This is very similar to the Dyna design. The phase splitter in this case is unbalanced, which is not a good design practice- you want anode and cathode resistors to be matched and equal. Even then, the drive voltage requirement for the 6L6GC will be straining things a bit, but you could probably get away with it. You'll want to adjust the compensation and lead cap for stability and bandwidth to accommodate the new tubes.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 13th August 2014, 04:41 AM   #8
diyAudio Member
 
Join Date: Jul 2014
Location: The Netherlands
It biased at 42Ma right now..

SY:
On the schematic, which parts should be changed to what values? Thanks!
  Reply With Quote
Old 13th August 2014, 09:59 AM   #9
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
R35 should be 36k and matched to the cathode resistor (buy several dozen 36k resistors and find a pair that match as perfectly as possible, absolute value isn't critical). If your output tubes are decently matched, you'll get a significant decrease in distortion.

C17, C20, and R38 should be adjusted. This will have to be done experimentally using a square wave and dummy load. You want to minimize ringing while not killing the rise time, and then confirm stability by placing a few different values of capacitors (from about 0.5 to 5uF) across the dummy load.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 13th August 2014, 10:12 AM   #10
diyAudio Member
 
Join Date: Jul 2014
Location: The Netherlands
R23 and r35 matched 36k, ok.

The other changes are only do-able with a scope

Last edited by Dephazer; 13th August 2014 at 10:17 AM.
  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
FS:NOS 1954 Philips EL34 metal base quad 4 100% emission very rare quad EL34. ivershing Swap Meet 0 17th August 2012 02:07 PM
Need help with 6l6GC choices BlackUnikorn Tubes / Valves 19 5th August 2008 01:39 PM
El34 PP Vs. El34 PSE alexmoose Tubes / Valves 47 6th September 2006 05:44 PM
6L6GC/EL34 SE Stereo Design bartr0n Tubes / Valves 25 16th September 2003 06:03 PM
EL34 vs. 6L6GC for 1ST DIY Tube Amp? pjkunz Tubes / Valves 4 17th December 2001 02:51 AM


New To Site? Need Help?

All times are GMT. The time now is 11:43 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