Documenting SimpleSE FRED Problem - diyAudio
Go Back   Home > Forums > Design & Build > Software Tools
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Software Tools SPICE, PCB CAD, speaker design and measurement software, calculators

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 7th June 2009, 07:13 PM   #1
diyAudio Member
Join Date: May 2009
Default Documenting SimpleSE FRED Problem

I haven't noted quite this issue mentioned previously.

First power up, all transformers connected - no switches, including stand-by. No tubes. Edcor 120V:740V transformer. Blew 2A fuse.

Replaced 2A fuse, tried again thinking bad luck. Powered up, blew 2A fuse and put a hole in a C-90 thermistor.

Disconnected power transformer, powered transformer, no problem.

Put El Cheapo meter across secondary and powered up, blew fuse. Looked like shorted transformer secondary but it measured a pretty reasonable 49 ohms.

Checked HV connector on board and found high resistance continuity.

Removed DESI-12 FREDS (TubeLab specified parts) and all is well.

Initial power up shorted FREDS even though they weren't in-circuit (no switch). Subsequent testing of transformer secondary with El Cheapo meter shorted meter (meter rated at 750V, guess there's no margin in that rating).
  Reply With Quote
Old 8th June 2009, 12:02 AM   #2
diyAudio Member
Ty_Bower's Avatar
Join Date: Mar 2007
Location: Newark, DE
Look at the schematic. If a FRED shorts, it WILL short the high voltage secondary regardless of whether SW1 is closed or not. If you must use the FREDs, make sure you've got the Fairchild parts, not the IXYS.

See the memo here.
  Reply With Quote
Old 10th June 2009, 01:59 PM   #3
diyAudio Member
Join Date: May 2009
Thanks, and thanks for the link.

I realize the FREDs will short the HV. I was trying to emphasize that it wasn't related to switching transient (stand-by switch) as I had read on the TubeLab site.

But thinking about it, I guess a switch is a switch regardless how far upstream it is.
  Reply With Quote
Old 10th June 2009, 10:08 PM   #4
chrish is offline chrish  Australia
diyAudio Member
chrish's Avatar
Join Date: Oct 2003
Location: Sydney
With that transformer a GZ34 is going to give you around 450V (+/-), just what you want, and slow warmup is good for your output valves. I'd just keep the valve rectifier and cut out the SS completely.
  Reply With Quote


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
FRED diodes dognut Parts 0 20th February 2009 11:27 PM
in memoriam Fred N. AKA 807 Zen Mod Tubes / Valves 5 27th September 2005 01:41 AM
FRED's GO banG. : O ) jleaman Parts 8 22nd September 2003 02:09 PM
Fred Boards jleaman Solid State 7 27th January 2003 04:59 AM

New To Site? Need Help?

All times are GMT. The time now is 07:16 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2