Class A2 6JD5 Curves - 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 19th September 2013, 12:14 PM   #1
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
Default Class A2 6JD5 Curves

Got a couple of these 6jd5 tubes to test with them, very inexpensive. Some may find use for it. Curves taken with beam plate tied to the plate. Traced with my home made curve tracer. I have no way of measuring grid current in my setup. The driver in the curve tracer starts giving up at 50ma which would be close to the top of curves. Using a LME49810.
Attached Images
File Type: jpg 6jd5.jpg (109.2 KB, 210 views)
  Reply With Quote
Old 19th September 2013, 06:52 PM   #2
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
Looks like one could put an AB2 load line (350V B+) in there if the grid survives up to +6V. Mu is varying noticeably, high Mu at high voltage, lower (still very high) Mu at high current.
__________________
I want a Huvr-Board!!
  Reply With Quote
Old 20th September 2013, 01:57 AM   #3
diyAudio Member
 
Join Date: Sep 2013
I've run some 6JD5 curves with +6 volts on the grid. Nothing melted, but they sure got warm.

Some brands of 6JD5's have a really nice sharp low voltage knee, and others don't. I've got a project in the works using these in Class A2 or AB2 (haven't decided yet), and ran some curves on different brands: GE, Zenith, Sylvania, DuMont. The DuMont and Zenith were very similar with the knee at about 80 volts. The Sylvania had the knee at about 120 volts.

GE was the worst, with not much of a knee to speak of. In fact the GE curves didn't look remotely like the others, and I wonder if they just re-labeled a different tube as 6JD5.
Attached Images
File Type: jpg 6JD5_Zenith.JPG (62.3 KB, 154 views)
File Type: jpg 6JD5_GE.jpg (64.5 KB, 149 views)
  Reply With Quote
Old 20th September 2013, 04:36 PM   #4
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
Robert,

Do you have grid current readings? I can only guess from mine that it is over 50ma.
  Reply With Quote
Old 20th September 2013, 07:02 PM   #5
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
Anyone have curves for or try the others: 6JH5, 6JK5, 6HV5, 6HS5, 6HZ5
Seem to all be similarly rated.
__________________
I want a Huvr-Board!!
  Reply With Quote
Old 20th September 2013, 09:20 PM   #6
diyAudio Member
 
Join Date: Sep 2013
At the time, it never occurred to me to take grid current readings (I did these traces more than a year ago). I had to modify my homebrew tracer by adding a power MOSFET source follower to provide enough grid drive.

However, Joe Sousa posted 6JD5 traces on the RadioMuseum forum:
6JD5 Forward grid bias
He also ran a g1 I-V curve that shows about 40mA grid current when g1 voltage is +6V (worst case is with low plate voltage of 50V). Note, that his traces are labeled "6JD5 GE", but in an email exchange, he confirmed that it was a typo, and was actually a Sylvania tube.

In fact, it was Joe's work that originally sparked my interest in these tubes. He also ran curves for 6JK5, 6JH5, 6HV5 and 6HS5.

6JK5 Forward grid bias
6JH5 Forward grid bias
6HV5A Forward grid bias
6HS5 Forward grid bias

Notice that all of these other tubes are similar to the GE 6JD5 that I traced, in that none of them have a low voltage knee, making them less desirable for class A2 operation. And coincidentally, all of these other tubes that he traced were GE brand. I'm wondering if this may be a characteristic unique to the GE tubes, and maybe other brands such as Sylvania might have the more desirable low voltage knee.
  Reply With Quote
Old 20th September 2013, 10:47 PM   #7
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
Quote:
Originally Posted by Robert Weaver View Post
At the time, it never occurred to me to take grid current readings (I did these traces more than a year ago). I had to modify my homebrew tracer by adding a power MOSFET source follower to provide enough grid drive.
Thanks Robert

Can you share your circuit of the mod? Did you use a source resistor or ccs?

Alfredo
  Reply With Quote
Old 21st September 2013, 03:08 AM   #8
diyAudio Member
 
Join Date: Sep 2013
I used a 500 ohm source resistor. A CCS was unnecessary. The MOSFET is an NDP603 which was what I happened to have on hand. I've attached the circuit of my complete grid voltage step generator. The whole curve tracer is sync'd to power line frequency, so that I can use a simple AC line supply for the plate sweep voltage. Originally, my grid drive circuit was completely opposite polarity, and used a -15V supply and PNP transistors to generate negative grid voltages. And it didn't use the op amp. I just connected the wiper of R2 to the tube grid, since a negatively biased grid draws no significant current.

When I went to do the positive grid curve traces, it was easier just to build a new circuit with opposite polarity devices rather than modify the existing one. I included the op amp in the new circuit, because I was already using an LM3900 for plate current sensing, and had 3 unused ones in the quad package. This gave a bit more grid voltage range. This curve tracer circuit is in a constant state of flux, and I don't have a finalized design. I want to get the grid drive circuit to a point where it can cover a wide range from negative to positve voltages, without having to switch circuits.

BTW, What brand of 6JD5 did you use for your traces?
Attached Images
File Type: png StepGenPositive.PNG (78.8 KB, 94 views)
  Reply With Quote
Old 21st September 2013, 08:55 AM   #9
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi!

Thanks for sharing these curves. I have used these tubes in Class A1 only so far and at high plate voltages with good results. I used them as output tube and also as driver for the 211.

I mainly used the 6HS5 and 6HV5A.

Some info here:

VinylSavor: Tube of the Month : The 6HV5A

VinylSavor: Tube of the Month: The 6HS5

Best regards

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 21st September 2013, 12:24 PM   #10
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
Thanks for the schematic. My tubes are RCA.
  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
811a Class A2 jim Tubes / Valves 106 29th July 2013 09:59 AM
845 class A2?? Fuling Tubes / Valves 56 12th October 2009 07:52 PM
A2 curves and curvecaptor. dave slagle Tubes / Valves 11 10th November 2008 04:51 PM
811A amp Class A2 MartinV56 Tubes / Valves 9 19th October 2007 04:34 PM


New To Site? Need Help?

All times are GMT. The time now is 09:30 AM.


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