Loftin-White - 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 7th January 2006, 07:49 PM   #1
5u4 is offline 5u4  United States
diyAudio Member
 
5u4's Avatar
 
Join Date: Nov 2005
Location: N of Tampa
Default Loftin-White

Hi, I'm new to this group. I'm working on a new project (FI Primer Loftin-White 2A3) & could use some advise. I ordered a custom power transformer & it came back with no 5V rectifier winding, so I'm considering the possibility of using SS diodes. Not really sure how bias for the 2A3 is arrived at. Guess 99V comes from the SRPP after it warms up placing the 2A3 at zero bias during turn on since 2A3 warms up before 6SL7? But what about the 390K load resistor to voltage divider. It seems there would be about 99V at voltage divider as soon as 2A3 warms up? Is there still about 99V through the 390K at 2A3 grid since there's little or no load? Can someone advise if SS is a viable option or not? What about using a Thermometrics Inrush Current Limiter (CL-70, CL-80) in power transformer primary to let all voltages come up slow reducing currert surges? Finally a standby switch would work for sure as long as no mistakes are made in turn on sequence. I'm really not open to using a relay, timer, etc. except as a last resort. It seems a tube rectifier solves all these problems. My schematic doesn't seem to want attach, so here's a link....... <http://tinpan.fortunecity.com/saints...mer/2a3-se.gif>Thanks , Jerry.
  Reply With Quote
Old 7th January 2006, 08:23 PM   #2
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
SS rectification is definitely viable. Use 1200 PIV Cree Schottky diodes from Parts Connexion. Watch the B+ rail voltage carefully. It will be higher than you would get with vacuum diodes.

There are honest differences of opinion about the best place to put NTC inrush current limiters. I prefer them on the rectifier winding, as it allows some time for the filaments to heat before the B+ rises. A pair of CL150s wired to the ends of the rectifier winding will get the job done.
__________________
Eli D.
  Reply With Quote
Old 7th January 2006, 08:27 PM   #3
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
Make sure that the tubes starts conducting in the right order, or you might get into problems when it comes to direct coupled amps.
  Reply With Quote
Old 7th January 2006, 10:46 PM   #4
diyAudio Member
 
Join Date: Jun 2003
Location: Portugal
And , please 5u4, would you be kind to tell us how it sounds ?

Good 2006 to DiyAudio community .


tgtwkr
  Reply With Quote
Old 8th January 2006, 08:27 PM   #5
5u4 is offline 5u4  United States
diyAudio Member
 
5u4's Avatar
 
Join Date: Nov 2005
Location: N of Tampa
Thanks for the info about the zero recovery 1200v diodes, I have some Harris fast recovery diodes, but never heard of zero recovery. I will try them for sure. They're expensive, but not any more than a half way decent tube rectifier. I will post photos when I get her done, probably in a few months. OPT's are Transcendar, P-xfmr & choke are E-P.

Had another idea about how bias may work in this amp. Tell if I'm wrong. Since the 2A3 filament is at 144v, zero volts on the grid would place the 2A3 in cutoff. When driver warms up, 99v is applied giving -45v bias? Any DC experts out there?
  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
Loftin-White 5u4 Tubes / Valves 45 20th September 2013 06:49 AM
Can anyone explain me this Loftin White amp? Giaime Tubes / Valves 40 25th February 2013 03:28 AM
loftin white 801 amp Sheldon Tubes / Valves 27 18th April 2011 05:24 PM
Loftin-White Mod 5u4 Tubes / Valves 3 28th February 2006 02:21 AM
Definitely NOT a Loftin-White!! kianbach Tubes / Valves 7 14th April 2005 05:46 PM


New To Site? Need Help?

All times are GMT. The time now is 07:51 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