Improve this SP-11 HV supply? - 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 12th January 2011, 03:05 PM   #1
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Default Improve this SP-11 HV supply?

Phono section of this SP-11 preamplifier never worked -- traced it back to a wonky MC7812K which was depriving the phono section filaments. A few weeks ago the entire thing started popping fuses.

Well, digging in I've replaced the 1N4006's with UF4007's and upgraded the filter caps. Just wondering if the entire MOSFET/MC34071P regulator isn't worth an upgrade while the top is still off!

Click the image to open in full size.

I just posted the link to the rest of the schematic on the AR db -- ARCDB - SP-11
  Reply With Quote
Old 12th January 2011, 07:57 PM   #2
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Expensive enough ? Despite the complexity and the number of regulators !!, the 6.3V supply is rather hit and miss with no output decoupling to ground. What happens on start up is the regulators go close into current dropout limit/shutdown...limited by the large series resistors R140/141 ....(tungsten near s/c cold resistance).....long term reliability a question. I never like these types of circuits. Maybe the L series 1.5A versions are a better regulator.
A 25V rated electroytic cap working at 22V (0.9) unadjusted for AC variations questions reliability. A 40V rated component space permitting would do the trick.

richy
  Reply With Quote
Old 13th January 2011, 03:13 AM   #3
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
Get it working correctly first. Then modify.

I doubt you'd get much out of messing with the FET/op-amp regulators. Granted the MC34071 (Motorola TL071 equivalent?) doesn't have the highest AVOL or lowest noise in the world, but I doubt you can get significantly better ripple rejection without running into issues with HF stability. You might be able to get better 1/f noise in the regulator by using a bipolar rather than a FET for the pass device. But honestly, I'd leave it alone.

~Tom
  Reply With Quote
Old 13th January 2011, 01:06 PM   #4
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Turns out that one of the windings on the transformer was shot -- (the one for V2) what I discovered was that the secondary windings are twisted pairs of enameled wire. When I un-soldered the transformer it turned out that only one of the pair were soldered to their respective diodes. The other wire wasn't connected on one end! Thus the remaining wire had to handle 2x the current and failed.

The regulator for V2 should have had a diode across it --
  Reply With Quote
Old 24th February 2011, 08:02 PM   #5
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
I've found a couple more errors in the wiring of this preamplifier's power supply.
  Reply With Quote
Old 24th February 2011, 08:51 PM   #6
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
I wonder why they didn't put the current limiting resistors ahead of the voltage regulators -- would made the regulator do less work.
  Reply With Quote
Old 1st March 2011, 06:13 PM   #7
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
This will probably cause heart attacks in Minnesota -- slow-start filament regulator for V2:

Click the image to open in full size.
  Reply With Quote
Old 2nd March 2011, 11:38 PM   #8
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Was thinking that they were using twisted pair for the transformer wiring. This is the "offending" 12V secondary which had become detached (thus the phono pre had no filament voltage). Seemed strange that only 1 tube would cause a problem. The wires are twisted for some structural integrity, not lower resistance. There is, however, a similar problem for the transformer primary which has to be tackled.

Click the image to open in full size.
  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
HV lab supply hidnplayr Power Supplies 1 17th February 2010 12:25 PM
Is this a practical HV supply? keantoken Power Supplies 16 26th May 2009 11:48 PM
Improve fullrange PC Speakers? Genius SP-HF350X 3yE Multi-Way 4 18th October 2007 12:14 PM
HV supply please comment before building bembel Tubes / Valves 8 5th December 2006 10:16 AM
Help improve CDP power supply..... Fin Power Supplies 4 28th April 2005 11:38 PM


New To Site? Need Help?

All times are GMT. The time now is 11:21 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