Staircase generator Schematics - diyAudio
Go Back   Home > Forums > Design & Build > Equipment & Tools

Equipment & Tools From test equipment to hand tools

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 17th October 2003, 08:47 PM   #1
316a is offline 316a  England
diyAudio Member
 
316a's Avatar
 
Join Date: Dec 2002
Location: West London
Default Staircase generator Schematics

Hi ,
I'm working on a curve tracer/matcher for power valves using the X/Y inputs of a scope , but just run into problems ! The circuit uses full wave rectified (unsmoothed) DC and at present I've been using a 4017 decade counter / potential divider / diode matrix staircase generator to provide the grid bias . Clocking is derived from the 100Hz HT via 470k resistor with zener clamp on the clock pin . Seems to work ok testing a 12AU7 down to -8v in 1 volt steps but those crappy 4017s always seem to go 'funny' on some output pins at times (I've run into this problem before with some 4017's in nixie tube clocks) . It draws curves nicely (when it works that is!) but I really need to find a more suitable solution to the staircase generator design . Anyone have any ideas or point me to schematics on the web ? I may require a design for generating up to -150V in 10V steps so if anyone has any ideas on any high voltage op-amps I'd appreciate it (logic/digital is not my strong point , only used to dealing with 5 legged devices usually :-triodes ) Thanks !

316a
  Reply With Quote
Old 17th October 2003, 11:49 PM   #2
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Default Sample & hold

It's not too difficult to make a staircase generator with valves:

1 Clip your sinewave to produce a squarewave
2 Differentiate
3 By clamping or rectifying, use the positive tips to cause a valve to conduct
4 Arrange the valve to be in series with a resistor such that it becomes a switched current source/sink
5 Use the current source to charge a capacitor (low leakage type)
6 Feed the capacitor charge directly into the grid of a cathode follower

A stairstep will appear on the CF's output.

You will need a reset circut also. This is easily done by sensing the stairstep level and dumping the cap charge. The cap is best to be in the cathode circuit, for ease of dumping.

OK so I'm mad but there are less actual elements in my circuit that in a semiconductor equivalent. Also you can use "real" voltages...
  Reply With Quote
Old 18th October 2003, 09:02 AM   #3
316a is offline 316a  England
diyAudio Member
 
316a's Avatar
 
Join Date: Dec 2002
Location: West London
Default Re: Sample & hold

Quote:
Originally posted by dhaen
It's not too difficult to make a staircase generator with valves:

1 Clip your sinewave to produce a squarewave
2 Differentiate
3 By clamping or rectifying, use the positive tips to cause a valve to conduct
4 Arrange the valve to be in series with a resistor such that it becomes a switched current source/sink
5 Use the current source to charge a capacitor (low leakage type)
6 Feed the capacitor charge directly into the grid of a cathode follower

A stairstep will appear on the CF's output.

You will need a reset circut also. This is easily done by sensing the stairstep level and dumping the cap charge. The cap is best to be in the cathode circuit, for ease of dumping.

OK so I'm mad but there are less actual elements in my circuit that in a semiconductor equivalent. Also you can use "real" voltages...
John ,
This sounds ten times more complicated than what I had planned . How is this triggered ? I'm triggering at present using a simple zener diode clamp which works perfectly driving the clock pin of the 4017 counter . Got a suggested schematic ? I was expecting a reply regarding using a DAC driven by a binary counter to generate the staircase but I think I'll end up using a simple pot for testing power valves unless someone has a simple way of doing this . I don't really want to spend more than a few hours developing this idea : it's only for matching triode strapped PL509 which I can't fully test on the AVO

316a
  Reply With Quote
Old 18th October 2003, 11:14 AM   #4
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
I don't know if this is readable.

SS is probably easier!
Attached Images
File Type: gif stair.gif (6.2 KB, 153 views)
  Reply With Quote
Old 18th October 2003, 11:27 AM   #5
diyAudio Member
 
Circlotron's Avatar
 
Join Date: Jun 2002
Location: Melbourne, Australia
how about a 4020 ripple counter with it's first 8 (or whatever) outputs driving an R2R d/a converter. A web search will find the details.

Either that, or have the ripple counter outputs controlling relays that source 1,2,4,8 etc volts in some kind of series adding setup.
__________________
Best-ever T/S parameter spreadsheet.
http://www.diyaudio.com/forums/multi...tml#post353269
  Reply With Quote
Old 18th October 2003, 11:47 AM   #6
316a is offline 316a  England
diyAudio Member
 
316a's Avatar
 
Join Date: Dec 2002
Location: West London
Default 4020

Quote:
Originally posted by Circlotron
how about a 4020 ripple counter with it's first 8 (or whatever) outputs driving an R2R d/a converter. A web search will find the details.

Either that, or have the ripple counter outputs controlling relays that source 1,2,4,8 etc volts in some kind of series adding setup.

Already tried a 4017 which is a ten stager using a resistor ladder . The problem with relays is that I need to switch at 50Hz

316a
  Reply With Quote
Old 18th October 2003, 12:03 PM   #7
316a is offline 316a  England
diyAudio Member
 
316a's Avatar
 
Join Date: Dec 2002
Location: West London
Default Generator

Quote:
Originally posted by dhaen
I don't know if this is readable.

SS is probably easier!

John ,
Thanks , I get the general idea . I may try an adaptation After plotting a curve for a pl509 at -80V 300V I get the feeling that a cuve tracer may take it's toll on the valves as they're high gm . I've now added a stack of 25-0-25V transformers and can switch between different anode sweep voltages . Very interesting , at 0V the curves really do go straight . taking a few traces and placing a ruler on the 'scope and I'm getting Ra of about approx 400 ohms and mu of 4 at 300V . Like a WWII radar operator I'm drawing the lines on the scope screen then testing another valve !(must add more sockets and a switch!) The good thing is that these valves seem quite consistant (Tungsrams) and at 3 a throw I'll easily be able to make up a matched set for the next amp

316a
  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
staircase horn??? xtextedx Subwoofers 5 26th September 2008 04:20 PM
metal staircase into a giant speaker? james hodge Multi-Way 2 26th February 2008 03:55 PM
Staircase saturation in push-pull SMPS MMicke Power Supplies 19 5th April 2005 03:29 AM
negative ion generator schematics zx3chris Everything Else 14 29th May 2003 06:14 PM


New To Site? Need Help?

All times are GMT. The time now is 10:22 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