Tweeks on tubes - bring out the demagnetiserss - Page 4 - 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 2nd August 2004, 09:29 PM   #31
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Default OT, sorry

She WAS a babe, wasn't she? And one of the few signs that there is still any sanity left in France. But I got some pressure from one of the other forum members to change her out, so here you are, H.L. Mencken.
__________________
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 2nd August 2004, 10:06 PM   #32
diyAudio Member
 
Join Date: Apr 2004
Location: SF Bay Area
Hello all, I'm the one that started this whole mess with my beam deflection tube preamp. After I posted information on it, one of the other members mentioned that these tubes are very sensitive to magnetic fields and that sometimes they get magnetized which can cause performance effects. I decided to try this out. I made a demagnetizer out of a spool of wire and a 6.3V transformer and attached the tubes to a plastic tube and slowly moved them through the field.

The spectrums I posted were two representave ones out of many that I did. By the time these were made the tubes had been in and out of the sockets at least 4 times so it was not initial "pin cleaning". They had been "burning in" for several days. Every time I do a spectrum I turn on the tubes and let them sit for 15 minutes to have some form of standardization. For both before and after demagnetization I ran several spectrums over a period of an hour. Of course there were small differences between runs but they were much less than the differences between pre and post demagnetization.

I perfromed this on the two tubes I had and got similar results for both. Not identical but similar.

Note, the spectrums were for BEAM DEFLECTION TUBES, not regular triodes or pentodes. I am NOT saying the same thing is going to happen with a 12AX7.

Other people have decided to try this demagnetizing thing on "normal" tubes and some have found a sonic difference. I myself have not tried this so I can't comment on what effect it has.

Since the Initial trials I have done the demagnetizing thing on 4 more BDTs, on two of them there was a significant change, on the others there was not very much of a change. All 4 of these tubes were GE, but two of them were in slightly shorter boxes than the others and had nice clear markings, the other two had somewhat deteriorated markings. I got the impression that two of them were much newer than the other two, so either manufacturing changes had taken place or the two older ones had been magnetized more by sitting around in the same location for a longer period of time. I did not perform exhaustive tests on these, that wasn't the goal, I'm trying to get good sound not a thesis.

Given that I can clearly hear a difference when demagnetizing on some tubes I'm going going to continue doing this when I get new tubes. So far the sample is pretty small (6 tubes) so I have not come up with any way to know in advance which will benefit from the procedure so I'm going to continue performing it on any new BDT tubes I get. It takes only a minute to perform and CAN make a big difference.

John S.

John S.
  Reply With Quote
Old 2nd August 2004, 10:19 PM   #33
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
John, many thanks for the follow-up!
__________________
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 3rd August 2004, 03:56 PM   #34
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally posted by John Swenson
Hello all, I'm the one that started this whole mess with my beam deflection tube preamp.
John S.
And a fine mess you've gotten us into....thanks a lot, John...

Um, John? what is a beam deflection tube? Sounds like it relies on beam steering for amplification, instead of the pinching of the stream... (I know, I know..simple question...problem is, I lost my near and dear RCA tube manual back in, I think, '74..I'm lost without it..)

In all your trials, did you try magnetizing any tubes to see if you could make it worse?

Cheers, John (oh no..not another one..)
  Reply With Quote
Old 3rd August 2004, 04:56 PM   #35
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Beam deflection tubes use electrostatic deflection, 7360 I think is one of them (among other types in the 6V heater range). Popular among shortwave radios because you can modulate/demodulate SSB with them.

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 3rd August 2004, 05:11 PM   #36
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally posted by Sch3mat1c
Beam deflection tubes use electrostatic deflection, 7360 I think is one of them (among other types in the 6V heater range). Popular among shortwave radios because you can modulate/demodulate SSB with them.

Tim
Thanks Tim...those things can certainly be altered by magnetic fields...

I figured only my tv set worked like that...well, ok...that and the particle collider rings I build magnets for..

Cheers, John
  Reply With Quote
Old 3rd August 2004, 05:34 PM   #37
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
Default Beam Deflection Tubes info

"what is a beam deflection tube"

http://basenjes.de/tubes/images/6ar8/6ar8.htm

and general tube design:

http://www.mif.pg.gda.pl/homepages/f...D62/index.html

http://www.mif.pg.gda.pl/homepages/f...RCA/index.html

Don
__________________
I want a Huvr-Board!!
  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
Marantz PM66 KI tweeks Fidelity Audio Solid State 506 25th January 2014 04:26 PM
Quad II Mods/Tweeks slurb.net Tubes / Valves 62 16th June 2012 12:32 AM
expert tweeks for PA? Pbassred Multi-Way 4 7th December 2003 08:57 PM


New To Site? Need Help?

All times are GMT. The time now is 09:37 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