Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Blowing fuses
Blowing fuses
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
Thread Tools Search this Thread
Old 4th March 2005, 05:48 PM   #1
balance is offline balance  Canada
diyAudio Member
Join Date: Nov 2004
Location: Montreal
Default Blowing fuses

Hello fellow DIYers,

This is my first post on diyaudio, but I must admit I am a lurker. Iím not new to diy audio, though somewhat new to tubes. I am looking to build a low watt SET some time soon, but am holding off until I can scrounge up the necessary parts. I have an old monoblock amp which I would love to salvage from, but I cannot bring my self to disassemble it since I think it is easily fixed. This brings me to my question.

This amp continually blows fuses on power-up, more precisely, when it is taken out of stand-by. This happens without any tubes installed. I don't think it is the power transformer, because it does not blow fuses without load (disconnected and isolated the secondaries.) I have checked the rectifier diodes with my DMM and they seem okay. However, I do not have any good way to test the filter caps under load. With a regular DMM, the caps seem to charge fine, however I suspect they are leaky under load.

Is there any easy way to test the caps short of swapping in known good ones? Are there other possible causes for blowing fuses like this that I've overlooked?

Thank a bunch. I appreciate any insight.

  Reply With Quote
Old 4th March 2005, 11:43 PM   #2
anatech is offline anatech  Canada
diyAudio Moderator
anatech's Avatar
Join Date: Jun 2004
Location: Georgetown, On
Blowing fuses
Hi Ed,
Possibly, should it have slow blow fuses installed? You can check the caps by putting a resistor in series with the diodes and measure the voltage drop. 100K will smoke under load, use 5W or better. The diodes go short and stay short when they break down, so I doubt it's them.

Is there a selenium rectifier stack in there? Normally used for bias voltage connected to the neg. end of a cap, pos. grounded.

Normally I check caps with a variable DC power supply and measure the leakage current across something like 10K ~ 100K depending on value and leakage current. That's if they pass the ohm meter test. I also tend to measure the capacitance as that changes a lot when they go defective in normal situations.

  Reply With Quote
Old 5th March 2005, 02:16 AM   #3
richwalters is offline richwalters
diyAudio Member
richwalters's Avatar
Join Date: Sep 2003
Location: Schwartzwald
Default Re: Blowing fuses

Originally posted by balance

I have checked the rectifier diodes with my DMM and they seem okay.

Welcome to the forum......you don't mention what type rectifier diodes you are using. HV Rectifier diodes have been known to <snap> avalanch when a peak secondary voltage occurs. make sure the PIV ratings are well up. The results may look good in dvm tests...the usual 0.6 V forward drop...but not at high AC. If a short was in an electroytic cap, the results would be more dramatic.

hope this helps

  Reply With Quote


Blowing fusesHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Keep Blowing Fuses Whiting Tubes / Valves 9 11th September 2008 09:44 PM
Car Amp help? Fuses blowing... Tolo Car Audio 1 3rd December 2007 01:42 PM
Help, new PSU blowing fuses TDWesty Chip Amps 14 4th March 2007 07:29 PM
blowing fuses homegrown45167 Car Audio 2 22nd October 2004 12:16 PM
The Fuses Just Keep Blowing raffir Chip Amps 19 22nd June 2003 03:49 AM

New To Site? Need Help?

All times are GMT. The time now is 12:30 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio