Safety questions - 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 31st January 2013, 03:16 PM   #1
mfaughn is offline mfaughn  United States
diyAudio Member
 
Join Date: Nov 2009
Location: Sylva, NC
Default Safety questions

I had a couple of questions and googling didn't help me come up with answers.

1) I've been told that the paper sleeves over can type power supply capacitors is there because the housing of the capacitor can be hot. Is this sometimes true? Often?

2) I know that one should not operate a tube amp without a load (i.e. speakers). Does this still hold true if you don't have any power tubes in the amp?
  Reply With Quote
Old 31st January 2013, 03:21 PM   #2
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Without power tubes there is no current flow through the output transformer.

Therefore, there is no risk to the output transformer, and it is acceptable to apply power for testing in this configuration.

Caviat - since the power supply is now unloaded, voltages will be higher than if tubes were installed. In a marginal design, this can lead to failure of the HV filter capacitors.
  Reply With Quote
Old 31st January 2013, 03:27 PM   #3
mfaughn is offline mfaughn  United States
diyAudio Member
 
Join Date: Nov 2009
Location: Sylva, NC
Quote:
Originally Posted by TheGimp View Post
Without power tubes there is no current flow through the output transformer.
That is what I thought but its nice to have it confirmed. Thanks.
  Reply With Quote
Old 31st January 2013, 04:23 PM   #4
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
A can type capacitor should not be hot in the temperature sense, otherwise it is not long for this world.

In many cases the outer case is connected to the negative terminal and the chassis, so should not be 'hot' from a voltage point of view either. However, this is not always the situation so the case is insulated. Usually by plastic, not paper.
  Reply With Quote
Old 31st January 2013, 04:33 PM   #5
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Cardboard insulated FP style cans were very common on US hifi gear and were often found in late tube era amps using full wave solid state voltage doublers such as found in the Harman Kardon Citation II and V, and IIRC some late Fisher tube power amps. HH Scott used FP cans with a positive case polarity (reverse of standard cap) in bias and filament supplies and these were sometimes covered with a cardboard case as well.

Plastic sleeves were not widely used here on FP style cans in my limited experience, in fact in that time frame American axial electrolytics frequently used cardboard sleeves. Japanese and European capacitor manufacturers embraced plastic sleeves a lot earlier IMLE..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 31st January 2013, 04:51 PM   #6
M Gregg is offline M Gregg  United Kingdom
diyAudio Member
 
M Gregg's Avatar
 
Join Date: Jun 2010
Location: UK
Quote:
Originally Posted by mfaughn View Post
I had a couple of questions and googling didn't help me come up with answers.

1) I've been told that the paper sleeves over can type power supply capacitors is there because the housing of the capacitor can be hot. Is this sometimes true? Often?

2) I know that one should not operate a tube amp without a load (i.e. speakers). Does this still hold true if you don't have any power tubes in the amp?

1...If the can is isolated from the chassis then it has the potential to become live..the can in most cases is negative or isolated internally..so if there is a metal can it should be at earth if exposed. Also be aware that a negative connection is not always negative Gnd. If its hot (temp) its going to blow out at some point. (Be wary of any metalwork that is not at Earth potential)

2...If you remove power tubes then ok the output section is not working, however there will be no load on the HT so it could go high value and take out the PSU caps if the rating is exceeded...also if you remove some preamp tubes be careful they are not DC coupled.. you could blow coupling caps if they are old..

NB I guess you already know it should have an isolation Tx..

Regards
M. Gregg
__________________
What is the sound of one hand clapping?

Last edited by M Gregg; 31st January 2013 at 05:09 PM.
  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
Safety ? west_nm Tubes / Valves 14 16th August 2010 10:59 PM
Safety First pacificblue Chip Amps 11 31st July 2009 06:59 AM
one safety question audio_moksha Tubes / Valves 3 6th February 2008 06:31 PM
Safety Guidelines Mad_K Everything Else 0 26th May 2006 07:45 AM


New To Site? Need Help?

All times are GMT. The time now is 06:38 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