Need a bit more power :) - Page 2 - 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 18th April 2013, 09:43 PM   #11
diyAudio Member
 
Join Date: Oct 2007
I'm searching something about these EL86, and I think it could be used with 300V on plates watching for bias. Datasheet says 250V on plates with 5.5k a-a and 14W RMS output, maybe 280V on plates and a max screen voltage of 220V could make some more Watt. I'm looking for 20W output.
  Reply With Quote
Old 18th April 2013, 11:42 PM   #12
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Tesla, you should be able to check the screen voltage at idle and prepare a loadline and then assess whether your screen resistor(s) are appropriate or causing some slide as you approach grid-current limiting of output power.

Are you bypassing the cathodes?

How much ripple is on your B+ at max output power?

How much is the plate-to-B+ OT primary winding resistance?
  Reply With Quote
Old 19th April 2013, 09:26 AM   #13
Tesla88 is offline Tesla88  Italy
diyAudio Member
 
Tesla88's Avatar
 
Join Date: Dec 2011
Location: Italy
Uhm , i don't have he amp on bench , i can check during week end. B +in my amp is at 280 without load (EL86 removed) and 260 at load , screens are connected to 250V trough a 1K/1W resistor , 250V comes from B+ with a R-C , 250V also supplies the PI stage.
Tried also differente cathode bias : Separate resistors , common resistors , CCS with lm317.
Actually the best is 2 resistors (one for each tube) by-passed by a 100uF cap.
El86 are biased at 45mA each with a 390ohm cathode resistor for each tube(10W dissipation). At full power current sourced to the center tap of Output transformer goes to 110mA at clip , 90mA at 0 signal.

EL86 seems to work well (and sound damn good and loud with master volume at full)
I Think EL84 works bad in this amp due to the low B+ voltage and impedance mismatch
Raa is near 4K

For Slideman , 20W sinus power from a EL86 pair is challenging , 16W are ok (biasing my amp at 55mA per tube i get 16Vrms @16 Ohm before clipping) and you don't notice the difference between 16 and 20 W !
  Reply With Quote
Old 19th April 2013, 02:29 PM   #14
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
Join Date: Dec 2012
Location: SF Bay Area
I'll tell ya this: If cap-bypassed, individual 390 ohm resistors are (so far) the "best", then the plan seems obvious. Since you've got relatively low plate voltage, increase amperage! That's so easy, that it just should be done.

How? Cathode resistor change. 330 ohm. "Next obvious number down" so to speak on the old fashioned (but perfectly suite) "10% sequence". Your bias becomes a bit less (hence higher plate current). The tubes still are in their design spec. The bypass cap (100 uF) is fine for each. Decent response down to 5 Hz. The WATTAGE of the bypass caps does not need to be 10 watts each. Use P = IR = V/R formulas. The 390, for instance: 45 ma = (0.045A)x390 = 0.78 watt. 10 watts... is overkill.

Anyway - here's a nice datasheet that'll allow you to get the most from these babies.

http://www.mif.pg.gda.pl/homepages/f...093/6/6CW5.pdf

GoatGuy
  Reply With Quote
Old 19th April 2013, 02:37 PM   #15
Tesla88 is offline Tesla88  Italy
diyAudio Member
 
Tesla88's Avatar
 
Join Date: Dec 2011
Location: Italy
When i wrote 10W dissipation , i was speaking about tube dissipation , not resistor , i used 3W resistors for cathode...I tried also more current using 330 Ohm resistors , the current was about 55 mA per tube or more , but not so much power increase , so i choose the 390 ohm to stay a bit low on dissipation meaning longer life of power tubes.
  Reply With Quote
Old 19th April 2013, 02:47 PM   #16
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
Join Date: Dec 2012
Location: SF Bay Area
Well (thanks for reply) - then it seems that 2 things are left: according to the PDF, a 2500 ohm plate load in PP seems to optimize output power. But the second thing is, what is the voltage swing on the DRIVE (the grid #1) for the tubes? [I think about that: you say you do go into clipping, so this really shouldn't be the problem. But worth the ask]
  Reply With Quote
Old 19th April 2013, 03:08 PM   #17
Tesla88 is offline Tesla88  Italy
diyAudio Member
 
Tesla88's Avatar
 
Join Date: Dec 2011
Location: Italy
You right , i'm not sure if drive is enough , due to the fact the power is now double compared to el84 i haven't check drive signal anymore and el86 require more drive voltage .
I'm really surprised by the 25W at 1% stated in the datasheet , i'm quite sure to get that power you have to go fixed bias , so this worth a try ! I'll check during the WE

Anyway , are PL84 same as El86 , except heater voltage ? I have a Tunsgram quartet of PL84 NOS ... i would like to make a stereo amp capable of 20-25W .

Also , anyone has got the Klein and Hummel TS60 schematic ? They use EL86 getting 25WPC.
  Reply With Quote
Old 19th April 2013, 03:18 PM   #18
MelB is offline MelB  Canada
diyAudio Member
 
Join Date: Feb 2005
Location: BC Canada
What voltage are you getting on the screens of your EL84's? The 1K resistor I think is too big. See how much voltage drop you have there. I'm looking at other designs that go as low as 250 ohm there or just use a choke to get the screen voltage up.
  Reply With Quote
Old 19th April 2013, 03:40 PM   #19
DF96 is online now DF96  England
diyAudio Member
 
Join Date: May 2007
PL84 and EL86 are the same apart from the heater.
  Reply With Quote
Old 19th April 2013, 04:33 PM   #20
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
Quote:
Originally Posted by slideman82 View Post
....14W RMS output.......
Maybe not so relevant, but this mistake is quite usual.

There is RMS voltage and RMS current, but no "RMS power".

U(rms) x I (rms) = Power or average power.
  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
Denon DCD 1520 20-bit or 18-bit? beauty_divine Digital Source 0 9th September 2007 07:41 AM
Using 20 bit data with a pair of old 16 Bit DAC stefanobilliani Digital Source 15 14th January 2007 01:55 AM
24 bit I2S source to 16 bit DAC? chris719 Digital Source 5 18th June 2005 06:24 PM
a bit of power, space and money mark_titano Multi-Way 0 27th November 2004 02:53 PM
use digital attenuation to improve 16-bit CD playback on 24 bit DAC capslock Digital Source 7 9th April 2002 12:18 AM


New To Site? Need Help?

All times are GMT. The time now is 03:25 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