DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 10 Dec 2018, 04:53

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 27 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post subject: Re: Power supply Cap
PostPosted: 15 Mar 2018, 16:52 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3853
Location: Arizona, USA
Hi, It seems to be a dual diode version with a common cathode. If it is functional it should work. It does make it difficult to test in circuit. If you temperarily remove the red wires then test each 1/2 of the rectifier separately it ought to be possible to see if either 1/2 if good/bad.

Having some ripple on the DC is quite common. The only way I know of to really get to low levels is by using a regulator.

I believe the component value of the choke is incorrect. 20 mH would not be worth the trouble, perhaps it is 20 H. I would use a larger first capacitor as well, at least 47 or 50 uF.

The voltage feeding the rectifier would be AC and not +250 and -250 which are DC values.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 16 Mar 2018, 11:51 
Offline

Joined: 09 Oct 2012, 19:43
Posts: 318
Location: Vancouver Canada
It's very common to be reading ripple voltage on the supply line. At the second cap you show a full ac wave then at the last cap you show a 1/2 wave with the other 1/2 missing. But then you mention you are adding the two probes. Don't. Just use one probe. At the first diode/cap/inductor junction, do you have full AC wave or is it the top or bottom 1/2 with a blank where the other 1/2 should be? If yes then one of the two diodes is gone. If you have a full wave showing the diodes are ok.
Amp hum can be a very elusive gremlin. Reading 5 mV ripple on the supply lines is nothing compared to 5 mV on the signal line. Your hum may be injected from the power trans location in the amp chassis in relation to the output trans. Can you send us a pic of the amp?


Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 17 Mar 2018, 12:38 
Offline

Joined: 13 Mar 2018, 06:32
Posts: 14
Attachment:
Schematic1.jpg
Same Amp different discovery. I am still trying to find the source of the hum. I have one amp with no hum and the 2nd amp with hum and they have the same schematic and parts. I looking around on what may be different I discovered that in the original Mullard push pull schematic that I have they tied both anodes of the 12ax7 together. That must be a mistake? I made this copy 4-5 years ago. Take a look.


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.



Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 17 Mar 2018, 14:33 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3853
Location: Arizona, USA
Hi, Actually not, I believe you are seeing the tube envelope and thinking it is a wire. The anodes are not tied together as one goes to each of the output tubes. The stage is a phase splitter so that the signal going to each of the outputs is 180 degrees different. This is needed for push-pull operation in this design. The cathodes are however tied together. See the difference in how the drawing was done.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 19 Mar 2018, 07:51 
Offline

Joined: 13 Mar 2018, 06:32
Posts: 14
I appreciate all the help each of you have given. I have learned a several valuable things. I am still working on the hum, however what I cannot figure out is 1 amp has no hum and the other a lot and they both should be the same. So I will still be looking trying to figure out what is different.


Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 19 Mar 2018, 17:50 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3853
Location: Arizona, USA
Hi, If the two amps are identical it shoul dbe fairly easy to track down the problem with a scope. Start at either the output side or input side and measure the hum on the scope. The compare it to the good amp. Move back one stage at a time until you find where they are the same. The stage you tested just before that one is where the problem is. If the amps are not the same all bets are off.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 20 Mar 2018, 14:12 
Offline

Joined: 13 Mar 2018, 06:32
Posts: 14
Looking back over the comments I received I noticed one referencing the power transformer may be bleeding into the power supply. That is definitely a possibility. The good amp has no ripple at all after the 2nd cap (at least less than 2mv). The bad one has a 6mV at the same spot. With both left and right inputs shorted, this 6mv gets sent to the anode on the 1st stage where it is amplified into the hum I hear. At the anode from the supply ripple and from the feed back ripple I have 10mv
showing up.


Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 21 Mar 2018, 06:16 
Offline

Joined: 13 Mar 2018, 06:32
Posts: 14
This was in deed the problem. The high voltage center tap was grounded to the frame and so was the PCB. This created a ground loop with the power transformer sitting underneath (on top actually). It's oscillating magnetic field went right through the ground loop. I re-routed the power center tap through the PCB and the ground loop vanished and so did the 6mv. A great day and w/o the suggestions of your responses I would have never found it. The amp now has zero hum...Thanks for the suggestions.


Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 23 Mar 2018, 04:13 
Offline

Joined: 13 Mar 2018, 06:32
Posts: 14
Can someone explain the effect of 5.0V vs 6.3V on the 6267's and 12AX7's? I have been running 5.0v to them and I'm wondering what I gave up or gained.


Top
 Profile  
 
 Post subject: Re: Power supply Cap
PostPosted: 23 Mar 2018, 05:06 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
With small tubes, there is a debate on shorter life and cathode poisoning. Best to stick to rated voltage +/- 5%

You will lose transconductance.

You gain in lower noise.

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 27 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy