#26 pre amp - Page 292 - 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 24th March 2013, 12:00 AM   #2911
CV6045 is offline CV6045  United Kingdom
diyAudio Member
 
CV6045's Avatar
 
Join Date: Mar 2013
Location: Portsmouth
Default 26

Abe, please send me the whole circuit diagram so I can look at it. I am sure there is a problem that will only show up on close examination


Quote:
Originally Posted by amandarae View Post
Hello,

Thanks for this! I tried understanding it but I am afraid I do not have a grasp of what it means.

My circuit is a AZ1 tube(I have 4Vac for filament). From spec sheet, I assume I am operating at about 2x300 V (Va max) and 100mA (Ia max). I am using a Hammond 250-0-250 power transformer.

After the tube, I have 20H then 47uF, then 10H, then 47uF, then 0.36H, then 47uF. Do you think there's something wrong as far as the L and C values according to the excerpts that you sent me?

Thanks,

Abe
  Reply With Quote
Old 24th March 2013, 02:19 AM   #2912
diyAudio Member
 
amandarae's Avatar
 
Join Date: Oct 2004
Location: Diamond Bar, CA
Quote:
Originally Posted by CV6045 View Post
Abe, please send me the whole circuit diagram so I can look at it. I am sure there is a problem that will only show up on close examination
Will do! I will draw it out.


Abe
  Reply With Quote
Old 24th March 2013, 03:19 AM   #2913
diyAudio Member
 
amandarae's Avatar
 
Join Date: Oct 2004
Location: Diamond Bar, CA
Quote:
Originally Posted by iko View Post
If I were you this is what I'd do.

1) work on one channel only
2) disconnect the filament regulator and replace it with a simple filtered 12V supply. If you have a computer supply it'll do. Or, power the filament from a 1.5V lab supply and bias the grid with a 9V battery. If it's still oscillating then it's the HV regulator that's got a problem. If it's not oscillating, then it's the filament regulator that needs fixing.

What I'm saying is, leave high quality aspirations aside for a moment, you're in debug mode now. Divide and conquer.
Agreed! I just do not have a power supply on hand. I will try to see if I can buy one tomorrow as Ebay takes longer.

thanks!

Abe
  Reply With Quote
Old 24th March 2013, 03:37 AM   #2914
Magz is offline Magz  United States
diyAudio Member
 
Join Date: Oct 2009
Location: New Jersey, USA
Quote:
Originally Posted by amandarae View Post
Hello Rod,
I sent pics to your email. Just in case, here they are.
Below are pics of two identical reg boards. The one with the heatsink was disconnected from the preamp. Second pic shows the underside. They are identical as far as components(omitting the transistors of course).
Click the image to open in full size.
Click the image to open in full size.



Below is a pic that shows the ground point on the main chassis. here, IEC, 0V, chassis, and cable shields connects to. The IEC from PSU chassis is taken here through the umbilical. The chassis connected to this point as well(which connects to IEC) is taken back to the PSU chassis through the umbilical.

The umbilical(8 pin)wiring is: +1 and -1(filament 1), +4 and -4 (filament 2), +3 and -3(B+, 0V), +2 and -2(chassis and shield, IEC GND). The last pic is the PSU chassis.


Click the image to open in full size.
Click the image to open in full size.

What's with the big blob of solder next to Q2 in the first picture? Is that contacting the body of the cap C1 next to it?

Q1 also looks like it has a solder blob not wetting the pad below it. Try cleaning those up.



.

Last edited by Magz; 24th March 2013 at 03:41 AM.
  Reply With Quote
Old 24th March 2013, 08:52 AM   #2915
diyAudio Member
 
amandarae's Avatar
 
Join Date: Oct 2004
Location: Diamond Bar, CA
Hello Guys!

Great news, I figured out what was wrong. It was not the extra filter cap at the filament reg board input using a long umbilical cord. It was the grounding of the individual filament raw DC supply.

Apparently, as stupid as I can be, I had the Negative and Positive raw DC supply outputs cris-crossed between the two floating supply! One positive is using the negative of the other! I found the culprit it at the umbilical cord connector.

Now, I am trying to optimize filament raw DC value as recommended to be around 16.5 to 18.5V.

To Rod, Andy, Iko, James(CV6045), Felipe, Magz, regal, nicoch58, and Tony. Thank you very much for your help and patience! Much much appreciated.

Cheers!

Abe
  Reply With Quote
Old 24th March 2013, 09:37 AM   #2916
CV6045 is offline CV6045  United Kingdom
diyAudio Member
 
CV6045's Avatar
 
Join Date: Mar 2013
Location: Portsmouth
Default 26

Good!!!! what a learning experience, I bet you know your way that amp with a blindfold on...... enjoy many hours of listening..........

Quote:
Originally Posted by amandarae View Post
Hello Guys!

Great news, I figured out what was wrong. It was not the extra filter cap at the filament reg board input using a long umbilical cord. It was the grounding of the individual filament raw DC supply.

Apparently, as stupid as I can be, I had the Negative and Positive raw DC supply outputs cris-crossed between the two floating supply! One positive is using the negative of the other! I found the culprit it at the umbilical cord connector.

Now, I am trying to optimize filament raw DC value as recommended to be around 16.5 to 18.5V.

To Rod, Andy, Iko, James(CV6045), Felipe, Magz, regal, nicoch58, and Tony. Thank you very much for your help and patience! Much much appreciated.

Cheers!

Abe
  Reply With Quote
Old 24th March 2013, 10:42 AM   #2917
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
Quote:
Originally Posted by amandarae View Post
Hello Guys!

Great news, I figured out what was wrong. It was not the extra filter cap at the filament reg board input using a long umbilical cord. It was the grounding of the individual filament raw DC supply.

Apparently, as stupid as I can be, I had the Negative and Positive raw DC supply outputs cris-crossed between the two floating supply! One positive is using the negative of the other! I found the culprit it at the umbilical cord connector.

Now, I am trying to optimize filament raw DC value as recommended to be around 16.5 to 18.5V.

To Rod, Andy, Iko, James(CV6045), Felipe, Magz, regal, nicoch58, and Tony. Thank you very much for your help and patience! Much much appreciated.

Cheers!

Abe
Great
  Reply With Quote
Old 24th March 2013, 11:52 AM   #2918
diyAudio Member
 
Join Date: Sep 2003
Location: London
"There will be more rejoicing in heaven over one sinner who repents than over ninety-nine righteous persons who do not need to repent......."
  Reply With Quote
Old 24th March 2013, 12:39 PM   #2919
Magz is offline Magz  United States
diyAudio Member
 
Join Date: Oct 2009
Location: New Jersey, USA
Nice troubleshooting!

I'd still clean up those solder joints, though. That's asking for trouble.
  Reply With Quote
Old 24th March 2013, 03:24 PM   #2920
diyAudio Member
 
amandarae's Avatar
 
Join Date: Oct 2004
Location: Diamond Bar, CA
Quote:
Originally Posted by Magz View Post
Nice troubleshooting!

I'd still clean up those solder joints, though. That's asking for trouble.
I did Magz! Thanks.

Abe
  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



New To Site? Need Help?

All times are GMT. The time now is 04:51 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