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 20 Feb 2019, 22:04

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 7 posts ] 
Author Message
PostPosted: 15 Jan 2019, 15:03 
Online
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3919
Location: Arizona, USA
Hi Folks, Tis' the month for strange thinking around here. :idea: I didn't know whether to post this here or in the Solid State section. Since it is going to be part of a tube design I figured here was better. Get out your thinking caps and sim programs. I have a design that needs to drop B+ from 240 to about 140 at 50ma and filter it really well. It would seem that a FET based series filter stage in the PS would do this as the third one in a string of CRC ones. Regulation is not all that important, but the drop and filtering are. I am considering bootstrapping a LR8 with something like and IRF820 (or 730 as I have both). It would seem that the filtering and regulating properties of the LR8 would be passed on to the FET and provide enhanced filtering. The adjustable output is a plus and regulation ought to be excellent. Any thoughts on this?

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 15 Jan 2019, 19:01 
Offline

Joined: 19 May 2011, 05:38
Posts: 34
try this: https://www.eleccircuit.com/the-variabl ... ly-0-300v/


Top
 Profile  
 
PostPosted: 15 Jan 2019, 19:10 
Offline

Joined: 23 Feb 2017, 02:02
Posts: 320
Firstly not sure why we want to drop to 140v from 240. A drop of 10-50v seems reasonalbe but not 100v.
Thats 100v and 50mA on the pass transitor and 5w, lots of expense on cooling and very poor efficency.

If you don't care about regulation much and no short circuit protection is required then I would personally go RC filter or zener + RC filter and bias on the power mosfet. Since its easier and can be low noise.

_________________
I've quit gaming during meal breaks, that allows me to be more constructive


Top
 Profile  
 
PostPosted: 15 Jan 2019, 19:32 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1538
Location: US Pacific Northwest
Do you have a target noise level for the 140V supply point (i.e. -x dB) and an estimate of the ripple level on the 240v supply? I am thinking that since you don't really care about regulation, and you're starting with a DC supply, with some noise level, a simple resistor and an LC filter stage may be sufficient. Definitely far simpler than a regulator IC.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
PostPosted: 15 Jan 2019, 19:55 
Offline

Joined: 23 Feb 2017, 02:02
Posts: 320
Heres a series regulator with short protection and feedback, current limiting at about 70-90mA.
The zener is 36v and the resistors are 0.5W.
Ay high voltage transitor will work something like mpsa42.
The 82k or 230k can be replaced with a adjustple resistor to adjust output voltage

Low noise and good.

http://tinyurl.com/ycyxlcyz
Be sure to click reset otherwise the simulation won't run properly.

I always design things on pen and paper but I didn't want to take photos out of my phone.


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


_________________
I've quit gaming during meal breaks, that allows me to be more constructive


Top
 Profile  
 
PostPosted: 15 Jan 2019, 20:25 
Online
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3919
Location: Arizona, USA
Hi, Thanks for the inputs. The reason for the drop is the PS is being used to provide 240 VDC for part of the circuit and I want to add something that needs the lower voltage. CRC filtering was not enough and there is no room for a choke etc. I can use the chassis for a heat sink so that heat is not a concern. I don't have ripple measurements at this time and may have to take some. I estimate from the breadboard hum that I need about 30 db of better filtering over a simple single stage CRC. It is the 4th in the string with the other 3 going to the rest of the cirrcuit. I'll post the project when I can get to my satisfaction. I was looking at something like what Mike567 posted, but figured it would cut the B+ down, but not clean it up enough.

Then again, maybe I am being fanatical again about hum and noise. It is there :eek: , I can hear it and I want it gone. :down:

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 16 Jan 2019, 03:12 
Offline

Joined: 23 Feb 2017, 02:02
Posts: 320
The zener diode used can be 1/4 watt and 36v tends to be commonly avalible and avalible in small packages. 47V or higher tends to be 2-5W packages only and more noisy.
If we make this zener diode a smaller votlage and then crank up the resistor ratio then the zener diode noise and vbe noise is amplified.

The output voltage is (VZener+VBE)(1+R1/R2)
VBE of the feedback transitor, R1 = 230k R2 = 82K

VBE of TO-92 typically arround 600mV at 1mA and 650 at about 8mA
Asuming zener or 36v and vbe of 600mv
We get (36+0.6)(1+230/82) = 139.25853V at output very close to simulation results.

The zener diode sets the emitter voltage of feedback transitor to a fixed constant 36v.
The independant point collector will change its voltage untill the base voltage becomes VBE higher than its emitter votlage thus acting as a feedback regulator.

The 470uF should have a 0.1uF in parallel to help kill high frequency noise and make output low noise.
I highly recomend the potential meter to replace the 82k as theres less voltage and power disipation on this one.

_________________
I've quit gaming during meal breaks, that allows me to be more constructive


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Bing [Bot], Exabot [Bot] and 11 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:  
cron
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