5AR4 @ 250mA - 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 24th February 2012, 11:49 PM   #1
diyAudio Member
 
scott17's Avatar
 
Join Date: Aug 2009
Location: JFK
Default 5AR4 @ 250mA

What about running a 5AR4 at max 250mA? Specifically the Sovtek variety. Anyone have any experience with this? Will the tube provide this current for a reasonable amount of time before failure?
  Reply With Quote
Old 25th February 2012, 12:54 AM   #2
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
The 5AR4 is rated for 825 mA RMS - and over 3 A peak... I doubt it'll fail at 250 mA.

~Tom
__________________
21st Century Maida Regulator, Universal Filament Regulator, Damn Good 300B, Novar Spud, and more...
Neurochrome : : Audio - http://www.neurochrome.com/audio - Engineering : : Done : : Right
  Reply With Quote
Old 25th February 2012, 01:06 AM   #3
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Both Russian and Chinese current production 5AR4s have weaknesses. The Russian stuff can deliver the rated 250 mA. of B+, but get into trouble at the high end of the rated voltage. OTOH, the Chinese tubes definitely can take Volts. However they get into trouble trying to deliver 250 mA.

Perhaps the best thing to do is use current production Russian 5AR4s and protect them, voltage wise, with UF4007s in the lines leading to the anodes.
__________________
Eli D.
  Reply With Quote
Old 25th February 2012, 01:34 AM   #4
diyAudio Member
 
scott17's Avatar
 
Join Date: Aug 2009
Location: JFK
Quote:
Originally Posted by Eli Duttman View Post
Both Russian and Chinese current production 5AR4s have weaknesses. The Russian stuff can deliver the rated 250 mA. of B+, but get into trouble at the high end of the rated voltage. OTOH, the Chinese tubes definitely can take Volts. However they get into trouble trying to deliver 250 mA.

Perhaps the best thing to do is use current production Russian 5AR4s and protect them, voltage wise, with UF4007s in the lines leading to the anodes.
Would the diodes be in series with the 50R resistors that I need for the series resistance factor?
  Reply With Quote
Old 25th February 2012, 01:36 AM   #5
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
Both Russian and Chinese current production 5AR4s have weaknesses.
So do JJ's. The problem seems to be an uneven cathode coating. The cathode heats up quickest where the coating is the thinnest. This area will try to conduct all of the current while the rest of the cathode is still warming up. These will usually blow, often spectacularly, at turn on. If you find a tube that survives start up a few times it will usually be OK for a year or two.

Using an inrush current limiter, or placing silicon diodes in series with each plate lead helps solve the start up issues.

I have an old Sylvania that has been in my SSE for nearly 7 years. That amp runs 230 mA. No issue with the tubes, but the power transformer gets really HOT!
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 25th February 2012, 01:37 AM   #6
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
Would the diodes be in series with the 50R resistors that I need for the series resistance factor?
Yes.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 25th February 2012, 02:13 AM   #7
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
Would the diodes be in series with the 50R resistors that I need for the series resistance factor?
The SS diode cathode leads get soldered directly to the tube socket. Be sure to use a hemostat or other clip on heat sink to protect the "sand", while soldering.

You might not need any series resistors whatsoever. It depends on the DCR of the power trafo's rectifier winding.

Authoritative 5AR4/GZ34 data sheet here.
__________________
Eli D.
  Reply With Quote
Old 25th February 2012, 02:18 AM   #8
diyAudio Member
 
scott17's Avatar
 
Join Date: Aug 2009
Location: JFK
Quote:
Originally Posted by Eli Duttman View Post
The SS diode cathode leads get soldered directly to the tube socket. Be sure to use a hemostat or other clip on heat sink to protect the "sand", while soldering.

You might not need any series resistors whatsoever. It depends on the DCR of the power trafo's rectifier winding.

Authoritative 5AR4/GZ34 data sheet here.
I have already calculated that 50R series resistance is required for the PT that I am using. Thanks for the info.

Scott
  Reply With Quote
Old 25th February 2012, 02:23 AM   #9
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
Authoritative 5AR4/GZ34 data sheet here.
Great data for it's time, 1958, but virtually none of todays production could survive 400+ AC volts into a 60 uF cap. I have seen other data sheets recommend a 47 uF. Even that might blow up a new tube. Most of my new builds have used a 33 or 39 uF.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 25th February 2012, 02:27 AM   #10
diyAudio Member
 
scott17's Avatar
 
Join Date: Aug 2009
Location: JFK
Quote:
Originally Posted by tubelab.com View Post
Great data for it's time, 1958, but virtually none of todays production could survive 400+ AC volts into a 60 uF cap. I have seen other data sheets recommend a 47 uF. Even that might blow up a new tube. Most of my new builds have used a 33 or 39 uF.
I'm using 30uF. No problems. No diodes either yet, but I'm only running at 200mA. I will increase to 250mA in the future when I get my new PT.

A question, do I even need the protection diodes? I'd hate to "sand up" an already sand-free design unless it was absolutely necessary.

Maybe just an inrush current limiter as suggested by George?

Last edited by scott17; 25th February 2012 at 02:52 AM. Reason: current limiter suggested by George
  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
where to get good 5AR4 's jlefevre1@me.com Tubes / Valves 19 29th November 2009 04:47 PM
Richardson 5ar4 Davec113 Tubes / Valves 13 4th August 2009 03:46 AM
FS:TI(Burr-Brown) BUF634T 250mA HIGH SPEED BUFFER YFW Swap Meet 2 3rd July 2008 02:15 AM
THAT transistor headphone amp (250ma discrete opamp) design sanity check. Russ White Headphone Systems 19 13th December 2007 12:52 PM


New To Site? Need Help?

All times are GMT. The time now is 07:12 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